text:
\section{Results}
\subsection{Strong-field ionization channels in SF$_6$}
ATI and HHG are closely related sub-cycle ionization phenomena. In ATI, strong field ionization (SFI) releases electrons into the continuum around every maximum of the laser electric field. This is repeated every optical cycle throughout the pulse. As a result, the photo-electron spectrum shows discrete peaks separated by the driving laser frequency $\omega$. The position of the peaks of this ATI comb is set by both the ionization potential and intensity dependent terms (channel-dependent Stark shifts, ponderomotive shifts U$_p$): KE$_{e^-}^j$=n$\hbar\omega$-I$_p^{j(s)}$-U$_p$, where I$_p^{j(s)}$ is the Stark shifted ($s$) ionization potential of ionization channel $j$, and n is an integer. At constant intensity, the ATI combs of different channels  give a direct measurement of their relative ionization potentials. In polyatomic molecules, where electronically excited cation states tend to undergo field-free fragmentation, different ionization channels can yield different fragments. This means that measuring
the ATI spectrum associated with a given fragment, using covariance or coincidence detection, provides direct identification of the SFI channel or channels.

\begin{figure}
\begin{center}
\includegraphics[width=0.5\textwidth]{FigCRATI}
\caption{(a) Channel-Resolved Above Threshold Ionization (CRATI) spectra of SF$_6$ at different laser wavelengths. Note that the spectra correspond to the SF$_5^+$ fragment; the ground state of SF$_6^+$ is unstable. The spectra are shifted vertically proportional to the laser photon energy. The diagonal lines indicate the expected position of ATI peaks from different ionization channels, for absorption of 7 (dark blue), 8 (blue), 9 (green), 10 (yellow) and 11 (orange) photons. (b) Calculated ionization yield for different channels at 800 nm. The X, A, B and C states are the ground and first three electronically (doublet) excited states of the cation.}
\label{FigCRATI}
\end{center}
\end{figure}

The CRATI technique, however, measures the channel I$_p$ modulo the photon energy. In general, if the energy difference between two ionization channels matches the photon energy of the driving laser, the ATI combs will be overlapping. More specificallyn, if the frequency of the driving laser field is resonant with a single- or multi-photon transition in the neutral or the ion, the ATI combs will also be overlapping. Therefore, in order to resolve the SFI channels, we varied the laser wavelengths between 400 and 800 nm (see Methods). This enabled us to follow the position of the ATI combs as a function of wavelength. The results are shown in Fig. \ref{FigCRATI}, where the ATI spectra associated with the dominant SF$_5^+$ fragment are shown for each laser wavelength. The diagonal lines indicate the expected position of the ATI peaks associated with the four lowest electronic states of the ion, for absorption of 7 to 11 photons. Clearly, multiple channels are present at all wavelengths. However, for the 800 nm
driving field, the multi-channel nature of the strong-field ionization process is obscured by the cation electronic states having energy level spacings which happen to be multiples of the driving field frequency. Therefore, for the case of SF$_6$, the variation of the driving field frequency was required in order to resolve the multiple SFI channels involved.

The CRATI measurements show that four main channels are involved in strong field ionization of SF$_6$, at all wavelengths. Quantifying the relative weight of these different channels would require knowledge of the branching ratios to each associated fragment. Unfortunately, these are unknown. In order to theoretically determine these weights, we calculated the tunnel ionization probability $P_{ion}^j$ for each channel $j$ by using a previously described approach \cite{spanner-pra,spanner13} and averaging over all molecular orientations. Ionization calculations used a 1/2-cycle 800-nm sin$^2$ pulse at 10$^{14}$ W/cm$^2$ peak intensity. The resulting weightings are shown in Fig. \ref{FigCRATI} (b). Two main factors determine the channel SFI rates: (i) the ionization potential of the channel -- the ionization rate decreases exponentially with $I_p$; (ii) the topography of the ionizing molecular orbital -- nodes in the plane perpendicular to the laser polarization tend to suppress the ionization probability. The
first effect was long considered to be dominant: SFI mainly occurs from the highest occupied molecular orbital, even though deeper channels can be observed under specific conditions, such as in aligned molecules. However, in a CRATI study of n-butane \cite{boguslavskiy12}, it was shown that excited state channels dominate over the ground state channel, despite their higher I$_p$s.  The results from Fig. \ref{FigCRATI}(b) are alike due to geometrical effects in SFI of SF$_6$ which overcome the exponential dependence on $I_p$, even for unaligned targets.

\subsection{Calculation of channel-resolved high-harmonic generation}
SFI involving multiple channels generates multiple interfering pathways in high-order harmonic generation. The harmonic signal is determined by the coherent sum over all possible channels (see Fig. 1). In the following, we present a simple model of HHG in which the SFI channels are considered to be uncoupled. Specifically, we assume that there are no sub-cycle non-adiabatic multi-electron transitions (NME) which would coherently couple cation states: an electron leaving a given cation electronic state will recombine to the same state.

The harmonic dipole moment is determined by the SFI probability, the propagation of the electron in the continuum, and the recombination cross section \cite{lewenstein94,le09}. The propagation in the continuum induces a dephasing of the harmonic emission, corresponding to the phase accumulated by the molecule between ionization and recombination. This is given by $\varphi^j=\Delta I_p^j \tau$ \cite{kanai07-2,smirnova09-1}, where $\Delta I_p^j$ is the difference between the ionization potential of the channel under consideration and the ground state ionization channel (X), and $\tau$ is the electron propagation time in the continuum, which increases with harmonic order from 0.6 fs to 1.7 fs for short trajectories at 800 nm. We make the approximation  that the recombination dipole moment $d_{rec}^j$ is equal to the field free XUV photoionization dipole moment. This was studied experimentally using synchrotron radiation and was the subject of accurate theoretical modelling \cite{yang98}. The simulated
photoionization cross sections from \cite{yang98} are shown in Fig. \ref{FigTheory}(a).

The harmonic intensity  $I^j=\left|P_{ion}^j d_{rec}^j e^{i\varphi^j}\right|^2$, calculated for each channel, is shown in Fig. \ref{FigTheory}(b). The picture, which is very complex in the case of photoionization where many channels have similar cross sections (Fig. \ref{FigTheory}(a)), appears  to be  simplified by SFI. The tunneling probability from the highest occupied molecular orbitals is significantly reduced by the presence of nodes in the orbitals, such that deeper channels are favoured, as illustrated in Fig. \ref{FigCRATI}(b). As a result, the harmonic signal is dominated by two channels, C and A, respectively below and above 25 eV. This property is quite remarkable: due to its sensitivity to tunnel ionization, high harmonic spectroscopy can isolate channels which may be difficult to distinguish in photoionization experiments (for instance, the A and B channels are not distinguished in XUV ionization). The maxima of the dominant channels are related to resonances in the photoionization cross
section: an autoionization resonance for channel C (5a$_{1g}\rightarrow$6t$_{1u}$) and a shape resonance (1t$_{2u}\rightarrow\epsilon$t$_{2g}$) for channel A \cite{holland92,stener06}.

The total harmonic intensity is calculated by coherently summing the signals from the different channels (Fig. \ref{FigTheory}(b)). The result shows a minimum between H15 and H17 of the 800 nm, around 25 eV. Changing the laser intensity modifies the electron propagation times in the continuum and therefore the relative phase $\varphi^j$ between channels. As a result, the shape and contrast of the minimum are modified, but its position is hardly affected.

\begin{figure}
\begin{center}
\includegraphics[width=0.5\textwidth]{FigTheory}
\caption{(a) XUV photoionization cross sections from \cite{yang98}. (b) Calculated harmonic intensity from different channels, and net response obtained by coherent superposition of all channels (gray area). The inset at right shows the highest occupied molecular orbitals corresponding to the different ionization channels. }
\label{FigTheory}
\end{center}
\end{figure}

\subsection{Experimental determination of SFI  channels}

\begin{figure}
\includegraphics[width=0.4\textwidth]{FigSpectrum}
\caption{Harmonic spectra generated in Ar (black) and SF$_6$ (red) at $I\approx1.3 \times 10^{14}$ W/cm$^2$. The argon spectrum is vertically shifted in order to improve visibility. }
\label{FigSpectrum}
\end{figure}

\begin{figure}
\begin{center}
\includegraphics[width=0.5\textwidth]{FigEllipticity}
\caption{The identification of SFI channels using elliptically polarized HHG. Measured harmonic signals as a function of laser ellipticity for H15 (a) and H21 (b) in argon (black dashed) and SF$_6$ (red continuous). The curves are normalized to the same area. (c) Calculated electron transverse momentum distribution in argon and the A and C channel from SF$_6$. (d) Measured response of the harmonic signal as a function of laser ellipticity in SF$_6$, normalized to that in Ar. The horizontal dashed lines are the theoretical normalized ellipticity-dependent responses for the A (green) and C (purple) channels, respectively. }
\label{FigEllipticity}
\end{center}
\end{figure}

Signatures of multi-channel contributions are readily observed in the HHG spectrum. In Figure \ref{FigSpectrum}, we show an experimental harmonic spectrum generated in SF$_6$ using 800 nm pulses at $I\approx1.3 \times 10^{14}$ W/cm$^2$. In order to distinguish the simple, single-orbital picture from the multi-channel case, we compared our measurement with argon, an atomic system with a similar ionization potential to the HOMO of SF$_6$. The SF$_6$ spectrum extends to higher orders and shows a pronounced minimum at harmonic 17, as was previously observed at a lower laser intensity \cite{lynga96}. Varying the laser intensity in our experiment does not modify the position of this minimum, as expected from our simple model. This minimum is a first indication that points towards a transition between channels C and A at around 25 eV (Fig. \ref{FigTheory} (b)). However, a definite identification of such a transition requires new methods in high-harmonic spectroscopy. These are discussed below.

How can we identify the involved channels without needing a full theoretical model of the harmonic emission? Such identification requires a differential measurement, a measurement which reveals the response of the molecular system to a variation of the laser parameters. This can be achieved by measuring the variation of the harmonic signal with laser ellipticity, $\epsilon$. The measured harmonic signal as a function of laser ellipticity in argon and in SF$_6$ is shown in Fig. \ref{FigEllipticity}(a-b). The harmonic intensity decays exponentially with $\epsilon^2$ \cite{ivanov96} and can be fitted by a Gaussian $I_q(\epsilon)=I_q^0 e^{-\beta_q\epsilon^2}$, where $q$ is the harmonic order and $\beta_q$ the variation with ellipticity. The ellipticity-dependent responses of argon and SF$_6$ are remarkably similar for harmonic 21 whereas that of argon is higher for harmonic 15.

High-order harmonic emission in an elliptical laser field can be described in a quasi-static semi-classical picture,  as follows. First, electrons tunnel out of the molecule with a finite transverse momentum distribution. This distribution is dictated by the molecular orbital structure, filtered through the tunneling process \cite{murray11}. If the electron wavepacket at the exit of the tunnel is spatially localized, then the momentum distribution is broad. The transverse momentum distributions associated with argon and the A and C channels in SF$_6$, calculated using the approach described in \cite{murray11}, are shown in Fig. \ref{FigEllipticity}(c). The distributions have a Gaussian profile, with the same width for argon and the A channel, while the C channel shows a broader distribution. This is consistent with the more localized character of the HOMO-3 (C) rather than the diffuse HOMO-1 (A). During propagation in the continuum, the electron wavepacket
spreads transversly. The spread of the returning electron wavepacket depends on the time spent in the continuum (and thus on the harmonic order, the lowest harmonics being emitted before
the highest harmonics \cite{mairesse03}), but also on the initial transverse momentum distribution: the broader the initial transverse momentum distribution, the broader the returning wavepacket. With an elliptically polarized driving field, the orthogonal component of the  field shifts the electron in the lateral direction, leading to a suppression of the recollision probability. Such suppression depends on both the trajectory length and the initial channel-specific transverse momentum. Therefore, the harmonic response $\beta$ as a function of  ellipticity serves as a fingerprint of the molecular orbital, i.e. of the SFI channel.

The variation  of $\beta_{SF_6}/\beta_{Ar}$ with harmonic order is shown in Fig. 5(d). Normalization to the response of argon suppresses the linear dependence of the ellipticity response  with harmonic order, which simply reflects the change in electron trajectory length. Above H17, the ellipticity responses  of SF$_6$ and argon are remarkably similar, while they differ by $\sim 20 \%$ for H15 and below. Theoretical ellipticity responses  are calculated using Gaussian fits of the distributions shown in Fig. \ref{FigEllipticity}(c) and reported, in Fig. 5(d), upon normalization to the argon response. They are in good agreement with experiment, given the simplicity of the model, and confirms the transition between the A and C channels at H17.

\subsection{Measurement of the relative phase between channels}
\begin{figure}
\begin{center}
\includegraphics[width=0.5\textwidth]{FigRabbit}
\caption{Measurement of the relative phase between HHG channels. (a) Principle of the RABBIT method: high harmonics photoionize argon atoms in the presence of an infrared (800 nm) field. Absorption of harmonic 15 and one IR photon, or absorption of harmonic 17 and stimulated emission of one IR photon both lead to  the production of the same sideband (SB16) in the photoelectron spectrum. (b) Phase of the sideband oscillations as a function of the delay between IR and harmonics. The experimental data points (with error bars) and theoretical results (solid lines) from saddle point analysis for the A (green) and C (purple) channels. To account for the response at SB16, we consider a transition from A to C channels between harmonic 15 and 17 (black dots). In this case, the relative phase between the two channels determines the magnitude of the signal  for SB16. The dotted lines are the results of simulations as a function of  relative phases $\varphi_C-\varphi_A$ varying from 0 to $\pi$ by steps of 0.05$\pi$. It
can be seen that the  experimental data agrees with the simulations for a relative phase  of $0.95\pi$. }
\label{FigRabbit}
\end{center}
\end{figure}

Elliptically-driven HHG in SF$_6$ revealed a transition in the channel dominating the emission process: harmonics 15 and below are produced by the C channel whereas harmonics 17 and above are produced by the A channel. In the following we use attosecond metrology to determine the relative phase between these two channels.

The RABBIT technique \cite{paul01} is an attosecond pulse characterization method which measures the relative phase between consecutive harmonics. RABBIT is based on photoionization of a target gas by high-order harmonics, in the presence of a weak fundamental laser field. The photoelectron spectrum shows main lines, resulting from the absorption of harmonics, and sidebands, corresponding to absorption of one harmonic and absorption or emission of an infrared photon (Fig. \ref{FigRabbit}(a)). Two quantum paths involving two consecutive harmonics lead to the same sideband, which results in an interference process. The sideband intensity thus oscillates as a function of delay between harmonics and the IR. The phase of this oscillation $\Phi^{SB}_q$ encodes the relative phase between the neighbouring harmonics $q+1$ and $q-1$: $\Phi^{SB}_q=\Delta\varphi_{q}+\Delta\phi^{at}_q$, where $\Delta\varphi_
q=\varphi_{q+1}-\varphi_{q-1}$ is the phase difference between harmonics $q+1$ and $q-1$ and $\Delta\phi^{at}_q$ is a scattering phase intrinsic to the target (the atomic phase, i.e. the phase accumulated by the photoionized electron in the atomic scattering potential \cite{paul01}).

In Figure \ref{FigRabbit}(b), we show the measured harmonic phase difference obtained using SF$_6$ as a generating gas and argon as a detecting gas. The harmonic phase difference increases with harmonic order but a clear deviation is observed at SB16, reflecting a specific phase difference between harmonic 15 and 17. A similar behavior was reported in \cite{rothhardt12}. Calculations of the harmonic phase, within the Strong-Field Approximation and using the Saddle Point method, were performed for the two channels expected to dominate the harmonic emission in this energy range: the A (green) and C (purple) channels. The resulting harmonic phase difference shows a similar increase with harmonic order for the two channels, reflecting the temporal dispersion of electron trajectories leading to emission of different harmonics \cite{mairesse03}. The calculations are in good agreement with the experiment for SB 18 to 22, associated with channel A, and for SB 12-14, associated with channel C. We note that a
transition from the C to A HHG channels between harmonic 15 and 17 would produce a shift in the phase of sideband 16. The electron trajectory leading to a given harmonic order slightly differs between the two channels, and this difference is enough to induce a significant effect on the phase accumulated along the whole trajectory. However, the results from this model do not agree with the experimental data: the calculated $\Delta\varphi$ for SB16 is around 1.3 rad while the measured phase shift is 4.8 rad. This shows that there is an additional dephasing of the harmonic emission between channels A and C which is directly measured by experiment. Therefore, the simulations were repeated with the introduction of an additional variable phase shift $\varphi_C-\varphi_A$ as an adjustable fit parameter (Fig. \ref{FigRabbit} (b)). Excellent agreement with the experiment is obtained when  $\varphi_C-\varphi_A =$ 0.95$\pi$. Importantly, this  phase difference arises from the phases of the recombination matrix elements
in the HHG process. Its determination illustrates the strength of this interferometric method in revealing the effects of shape resonances, autoionizing states and ionization phases in HHG \cite{haessler13}.

\subsection{Response of different channels to molecular vibrations}
\begin{figure}
\begin{center}
\includegraphics[width=0.5\textwidth]{FigDynamique}
\caption{The modulation of high harmonic generation by specific vibrations in ground state SF$_6$ molecules. Fourier transform of the intensity (a) and phase (b) modulations with pump-probe delay for harmonic 13 (dots) and 19 (line) showing the contribution of different Raman modes: $\upsilon_5$-T$_{2g}$ (524 cm$^{-1}$, yellow), $\upsilon_2$-E$_{g}$ (643 cm$^{-1}$, green) and $\upsilon_1$-A$_{1g}$ (774 cm$^{-1}$, blue). The contribution of each mode, obtained by integration of the peak in the FFT, is shown as a function of harmonic order in (c) intensity and (d) phase. }
\label{FigDynamique}
\end{center}
\end{figure}

We have identified the different channels operating in HHG from SF$_6$ by manipulating the electron trajectories in the generating mechanism. In the following, we vary  the nuclear degrees of freedom via vibrational excitation, resulting in systematic  modification of all stages of the 'interferometer'. As discussed below, this further   highlights the multi-channel nature of the HHG process.

Small molecular structural changes in the generating medium can induce significant modifications in the high-harmonic emission. For instance, Raman pump - strong-field probe experiments in SF$_6$ showed that the intensity of harmonic 25 to 45  varies by $\sim10\%$ upon molecular vibration \cite{wagner06}, even if the bond length variations remain small ($\sim 1\%$). Molecular vibrations may significantly change both the amplitude as well as the phase of each channel involved in the interferometer. First, changes in molecular geometry are expected to alter the vertical ionization potentials. Such modification influences the relative amplitude as well as the relative phase of each channel. For example, a 65 meV change in I$_p$ results in a 100 mrad phase change for a plateau harmonic. Second, molecular vibrations can lift the electronic degeneracy of molecular orbitals, increasing the number of possible channels. Finally, any distortions of the molecular orbitals associated with these  vibrations may affect
both the ionization and recombination dipole moments.

We have performed pump-probe experiments using an intense ($\sim 7\times10^{13}$ W.cm$^{-2}$) 800 nm pulse to Raman-pump vibrational modes in the SF$_6$ molecules and produce high harmonics in the excited medium. In addition to conventional experiments in which the harmonic intensity is measured (Fig. \ref{FigDynamique}(a,c)), we have used two-source interferometry to determine the evolution of the harmonic phase with pump-probe delay (Fig. \ref{FigDynamique}(b,d)) \cite{smirnova09,camper14} (see Methods). The harmonic emission is periodically modulated as a function of pump-probe delay. The typical modulation depth of the harmonic signals are  5$\%$ for the intensity and 100 mrad for the harmonic phase. Three of the six normal modes of SF$_6$ are Raman active vibrations: $\upsilon_1$-fully symmetric and strongly active mode $A_{1g}$ with a quantum of 774 cm$^{-1}$ (vibrational period of $\approx$ 43 fs), $\upsilon_2$-the doubly degenerate mode $E_g$ with a quantum of 643 cm$^{-1}$ ($\approx$ 52 fs) and
finally the triply degenerated $\upsilon_5$-$T_{2g}$ mode with a quantum of 524 cm$^{-1}$ ($\approx$ 63 fs) \cite{boudon04}. A Fourier analysis is performed to determine which vibrational modes modulate the signal (Fig. \ref{FigDynamique}(a-b)).

The weight of each vibrational mode in the intensity and phase modulations is extracted by integrating the corresponding peak and normalizing to the total signal (Fig. \ref{FigDynamique}(c-d)). The results show a clear transition around harmonic 17, consistent with the channel switching measured in static molecules. Below harmonic 17, in the region where the C channel dominates, the harmonic intensity is exclusively modulated by the $\upsilon_1$ mode. Above harmonic 17, the $\upsilon_5$ mode becomes slightly predominant. There is no significant contribution of the $\upsilon_2$ mode except for harmonic 13. Interestingly, the behavior of the harmonic phase is very different but also shows a transition associated to channel switching. The phase emission of C channel does not vary drastically for $\upsilon_1$ and $\upsilon_5$ nuclear dynamics and shows a weak contribution from $\upsilon_2$. The phase of the emission from the A channel seems insensitive to $\upsilon_2$ and dominated by $\upsilon_1$.

The complete calculation of the harmonic emission from vibrating molecules is beyond the scope of this article. As a first step, we evaluated the modifications of the strong field ionization yield resulting from molecular vibrations in the two dominant modes seen in the experiment: $\upsilon_1$ and $\upsilon_5$. For the C channel, ionization is maximized when the molecule is stretched in the $\upsilon_1$ mode, but shows no modulation in the $\upsilon_5$ mode. The ionization from the A channel shows modulations in both modes. This is in remarkable agreement with the measured modulations of the harmonic intensity (Fig. 7(c)), which suggests that when the strong field ionization yield is not modulated, neither is the recombination dipole moment.

\section{Discussion}
Multi-channel high-harmonic generation in polyatomic molecules is a rich and complex process which initiates a broad range of multielectron phenomena. The identification and isolation of the different channels is a major challenge which requires the development and integration of new experimental tools. In this work we introduced and combined several experimental schemes in an advanced spectroscopic study, enabling us to resolve multi-channel SFI in SF$_6$. First, we identified the different SFI channels by performing wavelength-dependent CRATI measurements. Varying  the wavelength addressed the issue of overlapping ATI combs which can occur at specific wavelengths, notably at the 800 nm driving frequency implemented in the majority of this work. We introduced a new scheme to HHG spectroscopy by resolving the spectral dependence of the normalized ellipticity response.  This measure enabled
isolation of the transverse shape of the electronic wavefunction at the moment of tunnel
ionization, removing the complexity imposed by the additional steps of the interaction. We made use of  the coherent properties of the process via RABBIT measurements which enabled the extraction of the relative phase between the channels. Such a measurement identified the important contribution of shape and autoionization resonances, hidden in many HHG measurements. Finally, we have made use of the nuclear degrees of freedom - via vibrational dynamics -- as an important control knob which manipulates both the phase and amplitude associated with each channel, advancing our ability to identify the multi-channel nature of the interaction.

We believe that the methods presented here will illuminate the complexity and the rich spectroscopic information obscured in many HHG experiments. For example, coupled with accurate calculations of the multi-channel harmonic emission, our results should facilitate  understanding the role of resonances in the emission process and also the elucidation of the influence of Jahn-Teller distortions in the ion \cite{walters09}.

The clear identification of the SFI channels is the first fundamental step in characterizing time-resolved multielectron processes, the long term goal being to resolve charge migrations or field induced coupling between the channels. We believe that it will be possible to isolate such dynamics by increasing the dimensionality of the experiment -- by scanning the fundamental wavelength of the strong laser field in HHG. Such scanning will scale the interferometer, presented in Fig. 1, enabling the decoupling of the different degrees of freedom involved in the process. Disentangling, for example, the contribution of resonances from dynamic features will be an important tool in HHG spectroscopy. In summary, we believe that the combination of methods presented here constitute an important building block for strong field spectroscopy and will lead to the discoveries of a broad range of multielectron strong field phenomena in complex targets such as polyatomic molecules.

\section{Methods}
\subsection{Channel-resolved Above-Threshold Ionization}
Experiments were performed using a Legend Elite Duo laser system (Coherent Inc.) that delivered 35 fs, 3.1 mJ, 800 nm pulses at 1 kHz (Molecular Photonics laboratory, NRC Ottawa). Laser fundamental pulses were implemented directly in the 800 nm experiments whereas $\sim$40~fs 400 nm pulses were generated through second harmonic generation in thin $\beta$-BaBO$_4$ crystals (150 $\mu$m thick). $\sim$40 fs 480 nm, 532 nm and 590 nm pulses were generated through sum frequency generation of the signal pulses from an optical parametric amplifier (Light Conversion, TOPAS-C) and the fundamental beam in thin $\beta$-BaBO$_4$ crystals (250 $\mu$m thick). Laser  pulses were focused with a f=50 cm spherical mirror onto a continuous, neat expansion of SF$_6$ molecules (expanded through a 50 $\mu$m pinhole $\sim$60 cm from the laser-molecular beam interaction region in a differentially pumped chamber). The molecular beam PEPICO (Photo-Electron Photo-Ion COincidence) spectrometer used to collect the resulting
photoelectrons and photoions has been described elsewhere \cite{boguslavskiy12}. Briefly, the kinetic energies  of the photoelectrons were resolved by time-of-flight using a wide-bore permanent magnet, magnetic bottle spectrometer. Photoions were collected using a coaxial pulsed-field Wiley-McClaren time-of-flight mass spectrometer. The photoelectron and photoion time-of-flight signals were post-processed using a covariance analysis \cite{frasinski92,Mikosch13} to correlate specific electron signals with the dominant SF$_5^+$ ions. The typical exponential ATI decay in energy has been substracted to enhance the ATI oscillations. This has to be described in the text (or methods).The resulting ATI spectra and experimental intensities were calibrated by argon and xenon ATI spectra recorded as a function of laser intensity.

\subsection{Calculations of strong field ionization rates}
Bound-state neutral and cation wavefunctions were calculated using aug-cc-pVTZ  basis set \cite{augccpvtz}, large-core effective core potentials \cite{stuttgartecp}, and RASSCF wavefunctions with 35 (cation) or 36 (neutral) electrons in 25 orbitals, allowing single and double excitations. For the cation, the active space was optimized for an equally-weighted average of the six lowest states of the cation (~X through ~D). The RASSCF vertical IPs were shifted uniformly by -0.512 eV.  At the equilibrium $O_h$ geometry (R(S-F)=1.575 Angstrom), the resulting cation state  energies are within 0.3 eV of the correlated MCQDPT2(27/28,21)/aug-cc-pVTZ values.

The magnitude of the vibrational distortions induced by an impulsive Raman pump was determined \cite{impulsiveraman} from normal vibrational modes and dipole polarizabilities,  calculated at the CCSD/aug-cc-pVTZ level \cite{ccsd-polar}. Calculated displacements assumed pump energy flux of $\approx 8.4$ J cm$^{-2}$. Pump and probe polarizations were assumed to be collinear, and were integrated on an order-9 Lebedev grid \cite{lebedevorder9}. RASSCF and MCQDPT2 \cite{mcqdpt2} calculations were performed with GAMESS-US \cite{gamessus}. CCSD calculations used CFOUR \cite{cfour}. Strong-field ionization calculations \cite{spanner-pra,spanner13} used Cartesian product grid with 0.18 Bohr spacing, extending to +/-18 Bohr from the origin, with an absorbing boundary \cite{manolopulous} of 9.4 Bohr at the box edges. The simulation used 14 spatial channels, corresponding to the ~X, ~A, ~B, ~C, and ~D
final states of the cation. Both laser and correlation coupling terms were included. Leap-frog time evolution used a time step of 0.003 atomic units.

\subsection{High-order harmonic spectroscopy}
The high-harmonic spectroscopy experiments were performed using the Aurore laser system at CELIA, which delivers 28 fs, 7 mJ, 800 nm pulses at 1kHz. High harmonics were generated by focusing the pulses with a f=50 cm lens in a continuous jet produced by a 250 $\mu$m nozzle backed by a few hundred mbars of gas. The emitted radiation was analyzed by an extreme ultraviolet spectrometer (1200 mm$^{-1}$ grating, dual Micro Channel Plates and a CCD camera).

To manipulate the laser ellipticity, two broadband zero-order waveplates were inserted in the laser beam: a motorized half waveplate in front of a fixed quarter waveplate. The harmonic signal was recorded as a function of the angle $\alpha$ between the half and quarter waveplate axis  which determines the laser ellipticity $\epsilon=tan(2\alpha)$.

For RABBIT measurements, we used the experimental setup described in \cite{loch11}. Briefly, the harmonic and infrared beams were delayed using a beam-splitting dichroic delay-line. They were focused by a toroidal mirror in a magnetic bottle time-of-flight spectrometer which recorded the electron spectrum produced by photoionizing argon atoms, as a function of delay between XUV and infrared beams.

Phase-resolved pump-probe experiments were performed by using a 0-$\pi$ phase mask \cite{camper14} inserted on the harmonic generating beam, before focusing. This mask created an interference pattern at focus, which resulted in the creation of two harmonic sources spatially separated by $\sim 100$  $\mu$m. In the far field these sources produced an interference patern, similar to Young's slits. A 800 nm pump beam was superimposed on one of the two sources, exciting the molecules by impulsive stimulated Raman scattering. The evolution of the phase of the harmonic emission as a function of pump probe delay was measured by determining the shift of the interference fringes, using a spatial Fourier transform.

\section{acknowledgements}
We thank R. Lausten (NRC), R. Bouillaud, C. Medina and L. Merzeau for technical assistance. S.P. acknowledges helpful discussions with and suggestions by M. Spanner (NRC). A. Stolow acknowledges NSERC (Canada) for financial support. We acknowledge financial support of the Conseil Regional d'Aquitaine (20091304003 ATTOMOL and COLA 2 No. 2.1.3-09010502), the European Union (Laserlab-Europe II N°228334), the Ambassade de France au Canada, and NSERC (Canada).

redpajama_set_name: RedPajamaArXiv


Favorite TV Show: Sherlock, The Walking Dead, Doctor Who, Castle, Psych, 30 Rock, Bones, Glee, हीरोस and Criminal Minds.
Favorite Movie: 500 Days of Summer, Inception, New बैटमैन movies, Red Eye, Perrier's Bounty, Hot Fuzz, Casino Royale are all I remember.
Favorite Musician: I like different songs from different artists, my संगीत taste's varied. Although I am going on a bit of a Maroon 5 kick for some reason.
Favorite Book or Author: Going Postal, HP, आप know, good books.
All It Takes. Xmas fic for Sophie.


text:
The double ratchet: Security notions, proofs, and modularization for the signal protocol
Joël Alwen, Sandro Coretti, Yevgeniy Dodis
Signal is a famous secure messaging protocol used by billions of people, by virtue of many secure text messaging applications including Signal itself, WhatsApp, Facebook Messenger, Skype, and Google Allo. At its core it uses the concept of "double ratcheting," where every message is encrypted and authenticated using a fresh symmetric key; it has many attractive properties, such as forward security, post-compromise security, and "immediate (no-delay) decryption," which had never been achieved in combination by prior messaging protocols. While the formal analysis of the Signal protocol, and ratcheting in general, has attracted a lot of recent attention, we argue that none of the existing analyses is fully satisfactory. To address this problem, we give a clean and general definition of secure messaging, which clearly indicates the types of security we expect, including forward security, post-compromise security, and immediate decryption. We are the first to explicitly formalize and model the immediate decryption property, which implies (among other things) that parties seamlessly recover if a given message is permanently lost—a property not achieved by any of the recent "provable alternatives to Signal." We build a modular "generalized Signal protocol" from the following components: (a) continuous key agreement (CKA), a clean primitive we introduce and which can be easily and generically built from public-key encryption (not just Diffie-Hellman as is done in the current Signal protocol) and roughly models "public-key ratchets;" (b) forward-secure authenticated encryption with associated data (FS-AEAD), which roughly captures "symmetric-key ratchets;" and (c) a two-input hash function that is a pseudorandom function (resp. generator with input) in its first (resp. second) input, which we term PRF-PRNG. As a result, in addition to instantiating our framework in a way resulting in the existing, widely-used Diffie-Hellman based Signal protocol, we can easily get post-quantum security and not rely on random oracles in the analysis.
Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings
Vincent Rijmen, Yuval Ishai
38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Eurocrypt 2019 - Darmstadt, Germany
Duration: May 19 2019 → May 23 2019
38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Eurocrypt 2019
Dive into the research topics of 'The double ratchet: Security notions, proofs, and modularization for the signal protocol'. Together they form a unique fingerprint.
Modularization Mathematics 100%
Ratchet Mathematics 95%
Security Proof Mathematics 90%
Cryptography Engineering & Materials Science 49%
Text messaging Engineering & Materials Science 46%
Function generators Engineering & Materials Science 42%
Hash functions Engineering & Materials Science 35%
Forward Security Mathematics 34%
Alwen, J., Coretti, S., & Dodis, Y. (2019). The double ratchet: Security notions, proofs, and modularization for the signal protocol. In V. Rijmen, & Y. Ishai (Eds.), Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings (pp. 129-158). (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); Vol. 11476 LNCS). Springer Verlag. https://doi.org/10.1007/978-3-030-17653-2_5
The double ratchet : Security notions, proofs, and modularization for the signal protocol. / Alwen, Joël; Coretti, Sandro; Dodis, Yevgeniy.
Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings. ed. / Vincent Rijmen; Yuval Ishai. Springer Verlag, 2019. p. 129-158 (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); Vol. 11476 LNCS).
Alwen, J, Coretti, S & Dodis, Y 2019, The double ratchet: Security notions, proofs, and modularization for the signal protocol. in V Rijmen & Y Ishai (eds), Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings. Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), vol. 11476 LNCS, Springer Verlag, pp. 129-158, 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Eurocrypt 2019, Darmstadt, Germany, 5/19/19. https://doi.org/10.1007/978-3-030-17653-2_5
Alwen J, Coretti S, Dodis Y. The double ratchet: Security notions, proofs, and modularization for the signal protocol. In Rijmen V, Ishai Y, editors, Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings. Springer Verlag. 2019. p. 129-158. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)). https://doi.org/10.1007/978-3-030-17653-2_5
Alwen, Joël ; Coretti, Sandro ; Dodis, Yevgeniy. / The double ratchet : Security notions, proofs, and modularization for the signal protocol. Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings. editor / Vincent Rijmen ; Yuval Ishai. Springer Verlag, 2019. pp. 129-158 (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)).
@inproceedings{d88449c68bac450389713e2ca06a6e3e,
title = "The double ratchet: Security notions, proofs, and modularization for the signal protocol",
abstract = "Signal is a famous secure messaging protocol used by billions of people, by virtue of many secure text messaging applications including Signal itself, WhatsApp, Facebook Messenger, Skype, and Google Allo. At its core it uses the concept of "double ratcheting," where every message is encrypted and authenticated using a fresh symmetric key; it has many attractive properties, such as forward security, post-compromise security, and "immediate (no-delay) decryption," which had never been achieved in combination by prior messaging protocols. While the formal analysis of the Signal protocol, and ratcheting in general, has attracted a lot of recent attention, we argue that none of the existing analyses is fully satisfactory. To address this problem, we give a clean and general definition of secure messaging, which clearly indicates the types of security we expect, including forward security, post-compromise security, and immediate decryption. We are the first to explicitly formalize and model the immediate decryption property, which implies (among other things) that parties seamlessly recover if a given message is permanently lost—a property not achieved by any of the recent "provable alternatives to Signal." We build a modular "generalized Signal protocol" from the following components: (a) continuous key agreement (CKA), a clean primitive we introduce and which can be easily and generically built from public-key encryption (not just Diffie-Hellman as is done in the current Signal protocol) and roughly models "public-key ratchets;" (b) forward-secure authenticated encryption with associated data (FS-AEAD), which roughly captures "symmetric-key ratchets;" and (c) a two-input hash function that is a pseudorandom function (resp. generator with input) in its first (resp. second) input, which we term PRF-PRNG. As a result, in addition to instantiating our framework in a way resulting in the existing, widely-used Diffie-Hellman based Signal protocol, we can easily get post-quantum security and not rely on random oracles in the analysis.",
author = "Jo{\"e}l Alwen and Sandro Coretti and Yevgeniy Dodis",
note = "Funding Information: While the formal analysis of the Signal protocol, and ratcheting in general, has attracted a lot of recent attention, we argue that none of the existing analyses is fully satisfactory. To address this problem, we give a clean and general definition of secure messaging, which clearly indicates the types of security we expect, including forward security, post-compromise security, and immediate decryption. We are the first to explicitly formalize and model the immediate decryption property, which implies (among other things) that parties seamlessly recover if a given message is permanently lost—a property not achieved by any of the recent "provable alternatives to Signal." We build a modular "generalized Signal protocol" from the following components: (a) continuous key agreement (CKA), a clean primitive we introduce and which can be easily and generically built from public-key encryption (not just Diffie-Hellman as is done in the current Signal protocol) and roughly models "public-key ratchets;" (b) forward-secure authenticated encryption with associated data (FS-AEAD), which roughly captures "symmetric-key ratchets;" and (c) a two-input hash function that is a pseudorandom function (resp. generator with input) in its first (resp. second) input, which we term PRF-PRNG. As a result, in addition to instantiating our framework in a way resulting in the existing, J. Alwen—Partially supported by the European Research Council under ERC Consolidator Grant (682815 - TOCNeT). S. Coretti—Supported by NSF grants 1314568 and 1319051. Y. Dodis—Partially supported by gifts from VMware Labs, Facebook and Google, and NSF grants 1314568, 1619158, 1815546. Funding Information: J. Alwen—Partially supported by the European Research Council under ERC Consolidator Grant (682815-TOCNeT). S. Coretti—Supported by NSF grants 1314568 and 1319051. Y. Dodis—Partially supported by gifts from VMware Labs, Facebook and Google, and NSF grants 1314568, 1619158, 1815546. Publisher Copyright: {\textcopyright} International Association for Cryptologic Research 2019.; 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Eurocrypt 2019 ; Conference date: 19-05-2019 Through 23-05-2019",
editor = "Vincent Rijmen and Yuval Ishai",
booktitle = "Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings",
T1 - The double ratchet
T2 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Eurocrypt 2019
AU - Alwen, Joël
AU - Coretti, Sandro
AU - Dodis, Yevgeniy
N1 - Funding Information: While the formal analysis of the Signal protocol, and ratcheting in general, has attracted a lot of recent attention, we argue that none of the existing analyses is fully satisfactory. To address this problem, we give a clean and general definition of secure messaging, which clearly indicates the types of security we expect, including forward security, post-compromise security, and immediate decryption. We are the first to explicitly formalize and model the immediate decryption property, which implies (among other things) that parties seamlessly recover if a given message is permanently lost—a property not achieved by any of the recent "provable alternatives to Signal." We build a modular "generalized Signal protocol" from the following components: (a) continuous key agreement (CKA), a clean primitive we introduce and which can be easily and generically built from public-key encryption (not just Diffie-Hellman as is done in the current Signal protocol) and roughly models "public-key ratchets;" (b) forward-secure authenticated encryption with associated data (FS-AEAD), which roughly captures "symmetric-key ratchets;" and (c) a two-input hash function that is a pseudorandom function (resp. generator with input) in its first (resp. second) input, which we term PRF-PRNG. As a result, in addition to instantiating our framework in a way resulting in the existing, J. Alwen—Partially supported by the European Research Council under ERC Consolidator Grant (682815 - TOCNeT). S. Coretti—Supported by NSF grants 1314568 and 1319051. Y. Dodis—Partially supported by gifts from VMware Labs, Facebook and Google, and NSF grants 1314568, 1619158, 1815546. Funding Information: J. Alwen—Partially supported by the European Research Council under ERC Consolidator Grant (682815-TOCNeT). S. Coretti—Supported by NSF grants 1314568 and 1319051. Y. Dodis—Partially supported by gifts from VMware Labs, Facebook and Google, and NSF grants 1314568, 1619158, 1815546. Publisher Copyright: © International Association for Cryptologic Research 2019.
N2 - Signal is a famous secure messaging protocol used by billions of people, by virtue of many secure text messaging applications including Signal itself, WhatsApp, Facebook Messenger, Skype, and Google Allo. At its core it uses the concept of "double ratcheting," where every message is encrypted and authenticated using a fresh symmetric key; it has many attractive properties, such as forward security, post-compromise security, and "immediate (no-delay) decryption," which had never been achieved in combination by prior messaging protocols. While the formal analysis of the Signal protocol, and ratcheting in general, has attracted a lot of recent attention, we argue that none of the existing analyses is fully satisfactory. To address this problem, we give a clean and general definition of secure messaging, which clearly indicates the types of security we expect, including forward security, post-compromise security, and immediate decryption. We are the first to explicitly formalize and model the immediate decryption property, which implies (among other things) that parties seamlessly recover if a given message is permanently lost—a property not achieved by any of the recent "provable alternatives to Signal." We build a modular "generalized Signal protocol" from the following components: (a) continuous key agreement (CKA), a clean primitive we introduce and which can be easily and generically built from public-key encryption (not just Diffie-Hellman as is done in the current Signal protocol) and roughly models "public-key ratchets;" (b) forward-secure authenticated encryption with associated data (FS-AEAD), which roughly captures "symmetric-key ratchets;" and (c) a two-input hash function that is a pseudorandom function (resp. generator with input) in its first (resp. second) input, which we term PRF-PRNG. As a result, in addition to instantiating our framework in a way resulting in the existing, widely-used Diffie-Hellman based Signal protocol, we can easily get post-quantum security and not rely on random oracles in the analysis.
AB - Signal is a famous secure messaging protocol used by billions of people, by virtue of many secure text messaging applications including Signal itself, WhatsApp, Facebook Messenger, Skype, and Google Allo. At its core it uses the concept of "double ratcheting," where every message is encrypted and authenticated using a fresh symmetric key; it has many attractive properties, such as forward security, post-compromise security, and "immediate (no-delay) decryption," which had never been achieved in combination by prior messaging protocols. While the formal analysis of the Signal protocol, and ratcheting in general, has attracted a lot of recent attention, we argue that none of the existing analyses is fully satisfactory. To address this problem, we give a clean and general definition of secure messaging, which clearly indicates the types of security we expect, including forward security, post-compromise security, and immediate decryption. We are the first to explicitly formalize and model the immediate decryption property, which implies (among other things) that parties seamlessly recover if a given message is permanently lost—a property not achieved by any of the recent "provable alternatives to Signal." We build a modular "generalized Signal protocol" from the following components: (a) continuous key agreement (CKA), a clean primitive we introduce and which can be easily and generically built from public-key encryption (not just Diffie-Hellman as is done in the current Signal protocol) and roughly models "public-key ratchets;" (b) forward-secure authenticated encryption with associated data (FS-AEAD), which roughly captures "symmetric-key ratchets;" and (c) a two-input hash function that is a pseudorandom function (resp. generator with input) in its first (resp. second) input, which we term PRF-PRNG. As a result, in addition to instantiating our framework in a way resulting in the existing, widely-used Diffie-Hellman based Signal protocol, we can easily get post-quantum security and not rely on random oracles in the analysis.
BT - Advances in Cryptology – EUROCRYPT 2019 - 38th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Proceedings
A2 - Rijmen, Vincent
A2 - Ishai, Yuval

redpajama_set_name: RedPajamaCommonCrawl


text:
Charles Pierre Amelot est un homme politique français né le  à Bost (Allier) et décédé le  à Cusset (Allier).

Médecin à Cusset, il est administrateur du district de Cusset au début de la Révolution. Il est révoqué par Fouché en l'an II. Il part comme médecin militaire en 1793, puis revient comme procureur de la commune de Cusset et membre du directoire du département. Il est élu député de l'Allier au Conseil des Cinq-Cents le 21 germinal an V. Il est nommé administrateur de la Loterie nationale et sous-préfet de Montluçon de 1800 à 1814 et de Gannat durant les Cent-jours. Révoqué par la seconde Restauration, il retourne à la Loterie nationale comme chef de division.

Notes et références

Bibliographie

Naissance en janvier 1760
Naissance en Bourbonnais
Décès en juillet 1816
Décès à Cusset
Député de l'Allier
Membre du Conseil des Cinq-Cents
Décès à 56 ans

redpajama_set_name: RedPajamaWikipedia


Creekside in Kenmore offers a coveted MAIN FLOOR MASTER SUITE layout with nearly 5,000 sf. of luxury living.
This well appointed 5 bed, 3.5 bath home offers a family rm, recreation room, bonus room with wet bar and a stunning light-filled studio.
You'll find space for everyone and every need with this beautiful new home all situated on an idyllic acreage lot with your own private access to the creek.
This home is perfect for hobbies, entertaining, or a home/work space.
Now complete and move-in ready!


text:
1943: Coast Guard Assigned the Sea-going Development of the Helicopter
Captain William J. Kossler USCG
CDR William J. Kossler USCG, a member of the Inter Agency Board, established to research and develop rotary-wing aviation, was convinced that the helicopter was the rescue vehicle of the future and would fulfill the future needs of the Coast Guard. As a member of this board he attended a very impressive flight test demonstration conducted by Sikorsky Aircraft Corporation on April 20, 1942. The demonstration caused great excitement at Coast Guard Headquarters resulting in a recommendation by CDR. Frank A. Leamy, the Aviation Operations Officer that several Sikorsky VS helicopters be purchased for training and experimental development. CDR Kossler advocated the purchase of three but neither the Engineer-in-Chief nor the Assistant Commandant was convinced. They stated that the acquisition of helicopters was not essential to the war effort and without the support of these two officers, next in rank to the Commandant, the future looked bleak for Coast Guard involvement with the helicopter.
The Helicopter as an Anti-submarine Weapon:
Kossler, although disappointed, was not about to give up. This was the period of an intensive and effective German submarine campaign off the east coast of the United States. He reasoned that the helicopters vertical take-off capability would enable it to operate from a merchant ship underway and provide protection from submarines. A series of events – some manipulated and others serendipitous – took place that would result in the development of the helicopter by the U.S. Coast Guard.
The Coast Guard air station at Brooklyn, New York was across the sound from Bridgeport, Connecticut which was the location of Sikorsky Aircraft. The Commanding Officer of the Brooklyn air station was CDR W.A. Burton who had accompanied Kossler on the first helicopter flight test demonstration. His Executive Officer was LCDR. Frank Erickson. Kossler had spent time with Erickson during a trip to Hawaii. The two men discussed search and rescue techniques and after Kossler's return to Washington, as the chief of the Aviation Engineering Division, the two men continued to exchange ideas. In the middle of June Kossler stopped by the air station and discussed the helicopter situation with Erickson. A few days after the visit, Kossler's assistant, LT. Bill Haley arrived at the air station. During lunch he casually mentioned that he had an appointment with Mr. Igor Sikorsky and wondered if anyone would care to fly him to Bridgeport. Erickson volunteered. Erickson met Igor Sikorsky and Michael Gluhareff, his Chief Engineer, and spent hours discussing the possibilities of the helicopter. Sikorsky put on a very convincing flight demonstration during which he repeatedly landed the helicopter within inches of a given spot. Erickson later stated that he did not realize that this whole sequence of events had been arranged ahead of time for his benefit.
CDR Frank Erickson, USCG
Erickson immediately started drafting a report for headquarters. The rescue capabilities of the helicopter were obvious but being aware of Kossler's setback he submitted a proposal for the development of the helicopter as an anti-submarine weapon. In the proposal he laid out specifics as to armament, aircraft capabilities, and utilization. He further stated that Coast Guard aircraft were presently flying anti-submarine patrols and it would be a natural for the Coast Guard to develop the anti-submarine capabilities of the helicopter. Burton strongly endorsed Erickson's proposal. Burton's endorsement pointed out that the Army had demonstrated its belief in the value of the helicopter by contracting for a number of the present models. His endorsement continued "Unfortunately the Navy has not shown any great enthusiasm for this type of aircraft. It is therefore, an excellent opportunity for the Coast Guard, with a very modest appropriation, to initiate and proceed with the naval development of the helicopter." Rear Admiral Stanley V. Parker, Commander Coast Guard Forces Third District also favorably endorsed it. Kossler noted that there was good reason for believing the Army would turn over a few of their machines for evaluation. This proposal for helicopter acquisition was approved by the Commandant in June 1942 — a month during which 55 merchant ships totaling 289,790 tons were sunk. A request was made for one YR-4 trainer and three XR-6 helicopters. The Navy designation for the YR -4 was HNS-1, the XR-6 was designated XHOS.
RADM Parker, who held Coast Guard Aviator Designation Number 7, was interested in seeing the helicopter. Erickson called Sikorsky and advised them of the request. They were delighted. Up until this time the highest ranking naval officer to see the Sikorsky helicopter was the inspector of naval aircraft at the Vought-Sikorsky plant and his primary interest was fighter aircraft production. Joined by Kossler, Erickson and Parker visited Sikorsky on the 21st of December, 1942. Igor Sikorsky and Michael Gluhareff gave the Admiral the "Red Carpet" treatment and put on an impressive demonstration of the capabilities of the helicopter. How effective is indicated by the following letter Parker sent to Admiral Waesche dated 24 December:
"Dear Admiral Waesche,
Although Admiral Land believes that we are already overcoming the German submarine campaign, it is still a serious menace which gives many of the responsible people in this war much concern.
Kossler and I saw the Sikorsky helicopter fly at Bridgeport. It is a remarkable thing, capable of taking the air and flying forward, sideways, and astern. Its control is almost unbelievable and it landed, for our edification, on the roof of a small building, on top of a pile of aircraft engine cases, on water, and flew along breast and at the same pace as a tugboat.
A couple of these with each convoy carried on the sterns of any convenient ships would give a degree of protection to a convoy in dangerous waters, which might be decisive.
A new model is being developed. Might not the Coast Guard be given the job of showing its application to convoy work? The newly projected machine will carry a bomb. It is of interest to note that the Navy Department official most closely in contact with the problem has given it very little encouragement. I think he is missing a bet. The Army is in the picture.
Kossler can tell you all about it. Maybe we can get on the bandwagon.
With best regards and wishes for the New Year,
(s) Parker"
Admiral Waesche decided to come to Bridgeport to see the helicopter for himself. On February 13 a flight demonstration using both the XR-4 and the VS-300 was conducted. Admiral Waesche was completely sold. On his return to Washington he addressed the issue of helicopter development with Admiral Ernest J. King, Chief of Naval Operations. As a result of this conference Admiral King issued a directive to the Chief of the Bureau of Aeronautics which ordered that testing and evaluation of helicopters be initiated and expedited to determine their practical value for operating from merchant ships in ocean convoys. The Bureau of Aeronautics was to carry out the tests with the Maritime Commission providing a typical merchant ship with suitable platform and equipment, and with the Army Air Force providing three of its YR-4A helicopters. The last paragraph was of the most significance to the Coast Guard so it is quoted in full.
"The sea-going development of helicopters and their operation in convoys will be a function of the Coast Guard. To this end Naval Aviators of the Coast Guard will be employed as practical in the early testing and evaluation of helicopters."
The next day Admiral Waesche sent the Engineer-in-chief a letter which quoted the above directive and stated:
"Captain W.J. Kossler, under your direction, shall be responsible for the development of the Coast Guard's part in this program. The project shall include the training of personnel and establishment and control of training stations until the project has been carried through the development stage and the training program has been placed on a routine basis."
Kossler lost no time with his new authority. That very day a confidential directive went out to the chief personnel officer soliciting volunteers to apply for training as pilots and mechanics in the new helicopter program even though a training program was not yet in existence. Two days earlier, Kossler had contacted Commander Labort of the War Shipping Administration urging a higher priority be given to a speedier delivery of the first of the YR-4As. The original date had been the latter part of April. On the 19th he was at Sikorsky's plant discussing training and technical matters. Test pilot Charles Morris was drafting a training syllabus. He and Colonel Frank Gregory USAAF, who was involved with the Army's helicopter test program at Wright Field, were the only two pilots qualified to teach helicopter flight. That left only Morris, limiting the initial number of qualified pilots. Kossler made arrangements with the Army Air Force and the Navy's BuAer for pilot and maintenance training. Erickson was selected to be the first Coast Guard Aviator to qualify as a helicopter pilot. Kossler's target date for the commencement of training was April. CMM Oliver Berry and Aviation MM1 James Boone accompanied Erickson and completed the mechanics course.
The Army chaired the Dorsey Commission and thus was involved in the development of the helicopter. Previously the Navy had not been interested and had not interfered. However, with the Coast Guard moving aggressively and assuming the role of developing the helicopter for the anti-submarine mission BUAER suddenly saw this development as their responsibility. Kossler was quietly informed that BUAER's interpretation of Kings directive was that the Coast Guard's role was subject to bureau's needs. The Commandant immediately sent a letter – authored by Kossler – to the chief of the Bureau of Aeronautics RADM John S. McCain asserting the Coast Guard's primary role in the development of the helicopter. A test of wills took place. It is not clear if Admiral King became involved but the climate at BUAER suddenly changed. On March 12 Kossler received a telephone call from CDR. McCoffrey USN, newly assigned at BUAER, informing him that a letter was being sent to ADM Percy Noble, head of the British admiralty delegation creating a joint committee to evaluate the helicopter. Members of the committee would be the British, the Coast Guard, and BUAER. The machines to be used were to come from the present Army procurement program now assigned to the British. Kossler was pleased with this for the British were also very interested in the development of the Helicopter and would be an asset.
In April Erickson showed Sikorsky and Morris a photo of a tanker broke in half after being torpedoed. The point of interest was a platform built on the deck amidships. Morris had already landed a helicopter on a platform at the Army's Wright Field. He and Sikorsky agreed a XR-4 could operate from a platform like the one depicted despite the obstructions of rigging and superstructure. Erickson passed this information to Kossler who immediately contacted R.W. Seabury, President of the War Cargoes Incorporated, who was extremely interested in protecting his merchant vessels. An arrangement was made for a meeting at the Sikorsky plant. After a thorough discussion and briefing on the potential of the helicopter Sikorsky asked Mr. Seabury if it would be possible to use one of his ships with a platform of the type under discussion. He said yes and immediately started making arrangements. Seabury then conferred with Admiral Davison of the Bureau of Aeronautics. He then called Kossler and told him that everything was ready and trials would be held the first week of May.
The tanker Bunker Hill was made available for the tests and a deck 78 feet long, with obstructions at both ends, was put in place. An eight foot bulls-eye in the center of a square was painted in the middle of the platform. Colonel Frank Gregory arrived on 6 May to fly the Army XR-4 provided for the tests. The entire helicopter project rested on the XR-4s ability to land on a ship. Gregory was concerned at first. His "shipboard" experience was limited to a stationary 20 foot platform at Wright Field. He immediately set about getting "additional experience." Gregory noted with reference to his first attempt:
"The space on the deck locked even smaller — It didn't look like the helicopter would fit. The cabin superstructure towered up like a two story building, and the people on it had that "it can't be done" look on their faces — yet the big white bulls-eye stuck out like a target — The XR-4 came true to the white marker as though being pulled by a powerful magnet, and a minute later the floats touched the deck."
He continued to practice landings and takeoffs that afternoon with the ship at anchor, then underway at five, seven and one-half, ten and fifteen knots. As the speed increased the landings became more difficult because of increased turbulence over the superstructure but the helicopter proved to be completely controllable.
YR-4 Hitting the spot on the Bunker Hill
The next morning guests were ferried out to the Bunker Hill. They included Representatives from the War Production Board, National Research Council, Representatives from the Office of Secretary of War, Army Transportation Corps, the delegation from Great Britain, Bureau of Aeronautics, Mr. Seabury of War Cargoes, , RADM Parker USCG, Kossler, Erickson and almost all of the top officials from United Aircraft- Sikorsky. A total of 97 names appeared on the guest list. Gregory put on an impressive and flawless performance as the ship cruised at various speeds up to 15 knots and on various headings with relation to the wind which was blowing at 12 knots. Everyone was very favorably influenced. Capt. Walter Diehl of the Bureau of Aeronautics, in a shift in attitude toward the helicopter, confided to Erickson that if he had seen a film of what just took place he would have been sure that it was faked. There would continue to be periodic assertions of authority on the part of the Bureau of Aeronautics but Kossler, with well placed support, was winning his battle.
The first meeting of the joint US-British Board for Evaluation of Helicopters for Anti-Submarine Warfare was held on 18 May, 1943. The board decided the test would be conducted in three phases. Phase 1 would be carried out in calm water such as Long Island Sound; Phase 2 would be carried out in the open seas; and Phase 3 would involve operation from a convoy on an Atlantic crossing. Two vessels were to be fitted with helicopter landing decks. The War Shipping Board turned the Governor Cobb over to the Coast Guard and the other was the SS Dagestan, a cargo vessel taken over by the British under a Lend-Lease agreement.
The second YR-4 scheduled to be delivered to the British and the third to be delivered to the Navy were due in early July. The Army had taken delivery on the first helicopter in May. This generated an immediate need to start a flight training program. One naval officer, two army officers and Erickson were in the first class. Les Morris, the Sikorsky Chief Test pilot was the instructor. Morris continued to give instruction to the British pilots involved in the program. The Army had stated that they did not see the development of the helicopter for ASW purposes their primary responsibility but were exceptionally supportive of the Coast Guard. A second helicopter demonstration was conducted by the Army on board the Army Transport James Parker on the sixth and seventh of July. The official observers included many of those who had been on the Bunker Hill, however, this was the first helicopter demonstration that CDR. James Russell of the Bureau of Aeronautics had seen. On the ninth of July, Russell turned in a very favorable report on the helicopter. Shortly thereafter the Bureau of aeronautics placed an order for 173 helicopters consisting of 23 HNS (R-4) trainers, 100 HOS-1s (R-6) with 225 HP engines and 50 HO2S (R-5) with the 450 HP engine.
CDR Charles Booth, the naval aviator in the initial class, was involved in moving the Navy's flight test facility from NAS Anacostia to the Naval Test Center at Patuxent River Maryland and as a result had not followed through on his qualification. Erickson thus remained the only naval aviator qualified in the helicopter. In the summer of 1943 Erickson took charge of the Navy's helicopter development program. On 3 September the Chief of the Bureau of Aeronautics requested that Erickson prepare a weekly report for the Bureau outlining the progress made on various model helicopters, estimates of completion, trial and delivery dates; and in addition, such other technical information determined from time to time which had or may have a bearing on present or future operations of this type aircraft. Erickson submitted his first report on 18 September. It noted that the YR-4s for the joint evaluation program were on schedule. The two British helicopters had been completed but had not yet been delivered because of rotor problems. He further stated the problems were being addressed. On 25 September a YR-4A was released to the British and the first Navy helicopter was accepted for delivery on 16 October. CDR Booth returned to complete his course at Sikorsky – It would be his responsibility to conduct aerodynamic, stability and performance tests on the new helicopters at Patuxent River as soon as one could be assigned. With the acceptance of two additional helicopters at the end of October the Sikorsky facilities became very crowded. Erickson sought to transfer all operation to Floyd Bennett Field. The Chief of Naval Operations approved and designated the Coast Guard Air Station Brooklyn as the Helicopter Training and Development Base. On 20 November LCDR John Miller USN and LTJG Stewart Graham USCG completed flight training. Graham received Coast Guard Helicopter Pilot Designation Number Two.
LT Stewart Graham departing the SS Daghestan in convoy during Atlantic crossing 16 January 1944
On November 23 a helicopter detail proceeded to Bridgeport to take part in the joint US-British ASW Evaluation Trials. The British SS Daghestan arrived the same day. Two helicopters were used – one British and one American. Weather was bad but improved by the 25th allowing for training flights in preparation for Phase 1. Among those observing was GEN Frank E. Lowe, Military Executive of the Special Committee Investigating the National Defense Program. He became an interested ally of Erickson. Phase one was essentially a repeat of the tests on the Bunker Hill. Phase two was conducted off Block Island. The most difficult condition under which operations were conducted was a wind of 42 knots over the deck, roll of four degrees, and a vertical deck movement of five feet. There were 328 landings made during this operation. The only major difficulty encountered was starting and stopping the rotor in high winds. Phase three consisted of operations from a vessel in convoy on the Atlantic crossing. The SS Daghestan sailed in convoy in January. Wind and sea conditions prevented any attempt at flight operations except for three days during the 16 day voyage. The ship's roll was never less than 10 degrees and during the worst conditions the roll increased as high as 45 degrees. Wind gusts were as high as 80 knots. A 30 minute flight was conducted on 16 January by LT Stewart Graham USCG and a 30 minute flight was conducted by F/L Jack Cable RAF. Both pilots, and later the Board, concluded that helicopters could operate from ships at sea but the performance of the helicopters presently available was too marginal to be operated satisfactorily off merchants ships in convoy.
There still existed, however, a possible defensive ASW role. In March of 1943 LCDR George Synon USCG, working as a researcher, advised Kossler of a sound device created by DR. Harvey Hayes. The device was to be suspended from a cable and lowered into the water to search for submarines. The letter stated that this could possibly be operated from a helicopter. It was not followed up on at the time because there were only two helicopters in operation, both with limited capabilities. Evaluations were made using Lighter-Than–Air craft. This did not prove to be satisfactory and development stopped. In December of 1944 under the direction of LT. Roy Rather USN the earlier efforts of Dr. Hayes were reopened. Dr. J.J. Coop, who had earlier been involved, assisted. On 12 January the Vice Chief of Naval operations was directed to make available the Hayes equipment to the Anti-Submarine Development Detachment. Technical assistance was to be provided by the Bureau of Ships and the Naval Research Laboratory. The Coast Guard was directed to provide the helicopter and crew. This would later prove to be the thread that kept the development of the helicopter going and is covered in a later narrative in this Time Line.
The helicopter as a Rescue Vehicle
New and more powerful helicopters being developed would have been able to operate off the merchant ships but the submarine threat had decreased substantially and it was obvious the helicopters would not be ready to play an important ASW role during World War II. During the testing and evaluation program modifications had been made and the ability of the helicopter to take off and land vertically had been successfully demonstrated. Nothing, however, had been done to take advantage of the helicopter's ability to hang motionless over a specific spot.
Preparations for the convening of a formal school to train pilots and maintenance personnel had continued through winter of 1943 and into the spring of 1944. LCDR O.R. Smeder USCG, in charge of ground school wrote most of the training manuals. Four additional Flight instructors had been trained and the first of 12 British Officers arrived 15 January. In May the Royal Navy flying School was set up at Brooklyn and would remain until 7 March 1945 when it transferred to the United Kingdom. A 40 by 60 foot landing platform that simulated landing conditions aboard ship by rolling five to ten degrees with a period of ten seconds became operational on 1 April. It was christened USS Mal de Mer. Soon actual landings were being made on the Cobb which had been specially equipped with a deck designed for this purpose. In addition a synthetic trainer, a flyable cockpit simulator, an effective training device ahead of its time, was designed and fabricated. Erickson formalized the flight curriculum and the first six week course began on 4 June. Kossler attended the first class and completed the course on 1 July.
On 3 January, 1944 an event occurred that would provide the first test of a helicopter in an
emergency situation. The USS Turner, anchored off of Sandy Hook, New Jersey had an enormous explosion which was followed by a second 47 minutes later sinking the ship. The survivors were brought to the hospital at Sandy Hook. The weather was snow squalls and sleet, winds of 20 -25 knots and extremely reduced visibility, all airfields in the area were closed and blood plasma was needed. Admiral Parker called Erickson and asked if it was possible to pick up plasma at the Battery in New York and get it to Sandy Hook. Erickson answered "Yes." and within minutes he, with Walter Bolton as co-pilot, was on the way. The visibility was so low that considerable care was exercised passing around the ships anchored in Gravesend Bay. Wind was blowing off the buildings at the pick up area creating a considerable amount of turbulence. Weight restriction was a problem and in order to facilitate the delivery of the plasma, Bolton reluctantly stayed behind. Erickson had to back the helicopter out on departure. It was evident that the weather conditions were such that no other type aircraft could have completed the mission. It was so noted in a New York Times editorial dated 6 January.
USS Mal de Mer simulated shipboard landing platform.
In April, when Admiral Waesche testified before the House Appropriations Committee in support of the Coast Guard's procurement of helicopters he stated to the committee "The Coast Guard has been assigned the duty of carrying on extensive experimentation in connection with the use of helicopters, both aboard ship and at coastal stations in connection with both anti-submarine warfare and air-sea rescue operations." This may have been a stretch at the time but it indicated that the Commandant was aware of the rescue capability evaluations that Kossler and Erickson were engaged in. This was the first official recognition of the search and rescue potential of the Helicopter.
To fully utilize the capabilities of a helicopter a method of lifting a person from peril while the helicopter was in a hover had to be developed. The first attempt was to devise a net suspended from the helicopter that would scoop a person out of the water. Tests showed that without a means to get the rescued person inside the helicopter the person scooped would be in the rotor wash and suffer the effects of hypothermia. Erickson proposed a modification to HO2S (R-5) helicopter in which the cabin would be widened to carry a stretcher case, doors that swung outward and up into the open position, and a motor driven hoisting unit. The problem with the plan was that he did not have an HO2S on hand. The only practical way to prove the hoist concept was to devise something simple that could be demonstrated on the HNS. A hoist boom and drum were connected to the rotary actuator and driven by a 12 volt motor with a high gear ratio. The cable had a pick up hook and harness. It worked well except the magnetic brake was apt to slip with a weight of over 200 pounds. The motor was changed to a Vickers hydraulic pump system permitting the hoisting of 400 pounds at a rate of two and one-half feet per second. The redesigned system worked perfectly.
The upgraded hoist system was installed at an opportune time. Captain Robert Dixon USN, the Director of Military Requirements, called Erickson inquiring about the hoist and asked if it could be demonstrated in a Navy Air Sea Rescue Exhibit Test Demonstration at the Naval Air station, Lakehurst on October 2, 1944. Erickson answered yes. This provided a weeks time to practice picking up people from rubber rafts. Arrangements were made for the use of the USCGC Cobb, which was equipped with a helicopter landing deck, as a base to carry out the tests. The Cobb anchored at Manasquan Inlet on the first and Erickson and Graham flew down to Lakehurst on the morning of the second. Not long after arrival RADM DeWitt C. Ramsey, Chief of the Bureau of Aeronautics, dropped by and looked over the rig. Just after 1300 Erickson and Graham flew out to the Cobb and spent the next several hours watching Navy rescue units demonstrate parachute drops, survival gear, and methods of egress from parachutes and aircraft after entering the water.
Igor Sikorsky – being hoisted to the helicopter
When it became time for the helicopter demonstration to start, four men wearing life jackets equipped with pick-up harnesses were put over the side in two rubber life rafts. Graham started the engine and when it had warmed up he took off and hovered 15 feet above the deck. He then hoisted a man up to the helicopter and lowered him to the deck testing the hoist and hovering performance of the helicopter. Seeing this, the observer boats all headed for the Cobb. Exactly on schedule at 1700 Graham flew off the ship and made a circle to approach the first raft from downwind. He hoisted a man up to the helicopter and returned to hover over the ship and lower the man to the deck. He repeated the routine for the other three men except for the last pick up during which he flew backwards from the ship to the life raft. All four pick-ups were completed in less than the ten minutes allowed. A rescue demonstration by a blimp followed the helicopter demonstration. They ran into troubles and required 45 minutes to lift one man from the water. The contrast between the helicopter and blimp was obvious. One man that was very much impressed was RADM Ramsey USN. From that day on the helicopter program had his unqualified support.
The Army Air Force was also impressed with the performance of the hoist and ordered twelve rescue hoists and visited the Coast Guard helicopter unit to copy details of the installation. The hoisting equipment was installed on the XHOS (R-6) and worked just as well. Sikorsky was impressed and submitted a proposal to the Army Air Force recommending this modification be made on all Army Air Force R-6s. The Army agreed. On 15 December RADM Ramsey conferred with Erickson to discuss the Navy helicopter program. He told Erickson he wanted all Navy helicopters equipped with hoists for rescue work. Erickson was directed to coordinate this with the Naval Aircraft Modification Unit at Johnsville, Pennsylvania.
Actual rescues continued and a number of different opportunities presented themselves to demonstrate the versatility and capabilities of the helicopter. The Brooklyn Navy Yard asked for the service of a helicopter one day a week for use in calibrating fire control radars on ships. It worked so well that the practice became common at other shipyards and would continue for several years. In October of 1944 an evaluation of the utilization of helicopters for spraying mosquitoes to control malaria was conducted.
The Coast Guard Helicopter Development Program Terminated
Events took place that led to the termination of the Coast Guard helicopter development and training program which had been established at Coast Guard Air Station Brooklyn.
In March of 1944 the Air Sea Rescue Agency was established when the Joint Chiefs of Staff requested the secretary of the Navy to establish an agency within the Coast Guard to conduct joint studies and assemble information on technical data, design of air sea rescue equipment, methods and techniques, and procedures including adequate facilities for air-sea rescue. The agency was to disseminate this information to appropriate agencies and maintain liaison with agencies of other nations. The Navy and the Army Air Force were to continue to provide search and rescue for their own operations. The Coast Guard was still part of the Navy at the time and was directed by the Navy to provide the men and material for search and rescue operations in the Continental Sea Frontiers. This function was carried out by the Coast Guard Office of Search and Rescue – not to be confused with the Air-Sea Rescue Agency. The number of authorized aviators was increased and fixed wing amphibians and seaplanes were provided. This was beneficial for the Coast Guard and solidified its claim to prominence in search and rescue operations. Many people involved in the search and rescue operation saw little or no benefit in the helicopter and some thought it to be detrimental.
Kossler and Erickson felt that just the opposite was the case. They strongly believed that the future of Coast Guard rescue operations involved having helicopters placed at small stations up and down the coasts, supported by air stations, and working in conjunction with Coast Guard cutters and lifeboats. Both men were visionaries that possessed the capabilities to turn a vision into reality and they did it well. Erickson was willing to assume authority, was direct and totally dedicated to the development of the helicopter. He was able to convince many of the value of the helicopter. These same traits would come to alienate those within the Coast Guard aviation establishment that he was not able to convince.
Senator Meade and two members of the Helicopter Subcommittee, senators Harley Kilgore and Homer Ferguson inspected the facilities on 17 February. They reported that they were pleased with the progress being made with the helicopter but time was running out for the helicopter program. With the end of the war in sight the large orders for helicopters were cancelled. Kossler was again in poor health and requested the Commandant transfer the helicopter program into regular channels. Headquarters aviation staff saw no use for the helicopter in the Coast Guard ASR operations and steps were taken to discontinue operations. Training classes at the school were canceled except for Navy personnel that would commission and operate the first Navy helicopter squadron. The majority of the helicopters were put in storage. The landing platform and training simulator were scrapped. Only enough helicopters were kept in service for the limited amount of training; the radar calibration flights that had been set up with the Navy for the ship yards at Boston, New York and Philadelphia: and the XHOS-1 which was scheduled for the testing of the Hayes sonar equipment as per direction of the Vice Chief of Naval Operations.
CDR Arthur J. Hesford USCG relieved Erickson as Commanding Officer of Coast Guard Air Station Brooklyn in March. Erickson was not transferred as is customary with relieved commanding officers nor was he reverted to executive officer or any other position in the chain of command. Erickson located in a small office and continued with the sonar project assigned by the Navy with little interference. It was not the best of circumstances for either Hesford or Erickson. Hesford was considerate and it was reciprocated. However, the relationship between Erickson and the headquarters staff is best described as acrimonious.
Erickson Continues
Erickson had been relieved; he had no command; but he still had the CNO's letter of 15 February 1943 ordering the development of the ASW helicopter. In January of 1945 LT Roy Rather USN and project engineer DR J.J. Coop reopened the earlier effort in developing underwater sound detection equipment. Within two months they believed they had the earlier problems solved and had a unit ready to install on a helicopter. During this period Erickson accepted a new XHOS-1. Rather and Coop arrived at Floyd Bennett Field early in March, ready to begin the tests.
Dr. Coop had been successful in eliminating the very high static noise of previous tests and the mechanical defects in the attachment of the Sonar head. The sound
XHOS with Sonar transducer under water
equipment was installed in the XHOS after modification of its small cabin to accommodate all components. Erickson suggested the helicopter sonar test be conducted from the Coast Guard Cutter Cobb. In mid April Erickson, Lt. Stew Graham, and others boarded the Cobb for the test area off Block Island, Long Island Sound. Erickson and Graham took turns piloting the helicopter with Coop and Rather alternating as sonar operators. To obtain Sonar readings the helicopter had to hover over one spot and keep the suspended sonar cable vertical while dipping the transducer below the water's surface. In order to do this a reference on the water was required. Float lights and dye markers were tried but the helicopter downwash swept both away. Surprisingly a sheet of the Sunday newspaper colored comics was found to soak up enough water and not blow away and could easily be seen from an altitude of 25 feet. While okay for these early tests an instrument was developed to tell the pilot when the cable was vertical.
The results of the tests proved that the Sonar equipment was sufficiently effective in locating and tracking the target submarine to warrant further development. Dr. Coop and his assistant redesigned the Sonar's electrical components and in January of 1946 the testing continued in Jamaica Bay and then at Key West, Florida.
Note: The further tests and ASW operations of helicopters is presented in this section under the heading; 1946 – Post War Helicopter Development.
The rescue capability of the helicopter was again displayed at the end of April. On 19 April a Canadian PBY-5A had been forced down 180 miles south of Goose Bay, Labrador. Two men were badly burned when the PBY caught fire after crashing in the wilderness. Several days passed before a USAAF C-47 spotted their distress signal. Two RCAF Norseman ski-equipped planes dispatched to the scene landed safely. One crashed on take off after taking aboard survivors. No injuries resulted. One managed to take off with the two burned survivors. A blizzard prevented any further attempts during the next two days. When the weather cleared, the Norseman returned and landed, but when the takeoff was attempted the skis became bogged down in the mushy snow and they could not take off with any survivors aboard. Both were stripped to reduce weight and later flown out without survivors. Rescuers anticipated the nine men left behind would be stranded for weeks until the lakes thawed sufficiently for float planes to land.
HNS-1 being loading aboard Army Air Transport Command C-54
The answer was the helicopter. The XHOS was loaded with sonar equipment and involved in the sonar testing. However, Erickson still had an operable HNS. Though lacking in range, and capable of carrying only one passenger, it was disassembled, loaded on an Army Air Force C-54 and flown to Goose Bay, arriving on the twenty-ninth. Working continuously the crew had it reassembled by the morning of the thirtieth. That morning Lt. August Kleisch, USCG, departed in the float equipped helicopter, burdened with seven five-gallon cans of gasoline lashed to the floats, for the 184-mile trip to Lake Mecatina via the survivor's camp. Kleisch, escorted by a Canadian PBY, landed about midway on the flight, refueled the helicopter from the gas cans and departed for the survivor's camp. The plan was to fly the survivors to the Mecatina radio range station located on an island in the middle of Mecatina Lake. This was 32 miles distant from the crash site and served as the base camp. Gasoline was available there. With a helicopter that flew the trip at 50 miles per hour only one man was evacuated on the first day. Kleisch continued the next day. The last survivor came out three days and nine round trips later on the afternoon of 2 May. The survivors were
LT. August Kliesch in helicopter – Canadian PBY crew – only one could come out at a time
flown from the base camp to Goose Bay.
News of this remarkable feat spread and even with a war on it captured the public's interest. Gen Lowe dropped by to see Erickson within days of the rescue bringing with him General Jacob L. Devers, US Army, for a helicopter demonstration. Devers had just returned from Europe to take command of the Army Field Forces. Erickson tailored his demonstration to his audience. The Army, moving ahead, assigned R4s to Liberty ships with landing platforms designated as Aircraft Repair Units in the Pacific.
On 1 May Lt. Carter Harmon USA in an R-4 (HNS-1) made the first Combat SAR helicopter pickup behind Japanese lines in Burma.
Erickson continued to promote the helicopter to all that would listen. In 1946 Erickson and a small dedicated group moved to a location on the Elizabeth City air station to continue development work.
The Growth Years
1939: Grumman JRF-2/3 and 5G Purchased
1939: Coast Guard Participates in the Neutrality Patrol
1940: The Coast Guard and the Birth of the Helicopter
1940: Coast Guard Air Station Elizabeth City Established
1940: Coast Guard Provides Aircraft and Crews for the US Coast and Geodetic Survey
1941: Coast Guard Air Station San Francisco Established
1941: The Coast Guard and the Greenland Operations
1941: Grumman J4F-1 Purchased
1941: Coast Guard Acquires Consolidated PBY-5/-5A/-6A Aircraft
1941: Coast Guard Aviation Anti-Submarine Operations
1942: The Coast Guard Acquires OS2U Kingfisher Aircraft
1943: Coast Guard Acquires Martin PBM 3/-5 Flying Boats
1943: The Development of Air-Sea Rescue
1943: Coast Guard Patrol Squadron VP-6CG Established
1944: Air Detachment Annette Island Alaska Established
1945: Coast Guard Auxiliary Aviation
1945: Coast Guard Acquires P4Y-2G Privateers for Air Sea Rescue Duties
1946: Coast Guard Air Station Traverse City Established
1946: Post World War II Coast Guard Search and Rescue
1946: Coast Guard Air Detachment Argentia Established
1946: Pacific LORAN and Post War Aviation Support
1946: Post War Helicopter Development
1946: International Ice Patrol – Aerial Surveillance Becomes Primary
1946: Coast Guard acquires PB-1G Long Range Search and Rescue Aircraft
1946: Operation HIGH JUMP
1947: Coast Guard Aircraft Repair and Supply Base Established
1947: Coast Guard Air detachment San Juan Puerto Rico Established
1947: Coast Guard Air Detachment Kodiak Alaska Established
1948: Coast Guard Provides Aviation Support for the Treasury Department's Alcohol Tax Unit
1949: Coast Guard Air Detachment Barbers Point Established
1950: The Korean War – Coast Guard Aviation Participation
1950: Coast Guard Air Detachment Corpus Christi, Texas Established
1951: The ASW Helicopter Becomes a Reality
1951: Coast Guard Acquires the UF-1G/2G Albatross Aircraft
1951: Coast Guard Acquires the HO4S Helicopter
1952: Coast Guard Air Detachment Arlington Established
1952: Coast Guard Air Detachment Bermuda Established
1954: Coast Guard Acquires Martin P5M Seaplanes
1955: Coast Guard Air Detachment New Orleans Established
1956: Promulgation of the National SAR Manual


Portable Metal Scrap Crushers 4.7 - 4832 Ratings ] The Gulin product line, consisting of more than 30 machines, sets the standard for our industry. We plan to help you meet your needs with our equipment, with our distribution and product support system, and the continual introduction and updating of products.
A car crusher is a piece of machinery used to compress the metal remains of a junked car after it has been Crushers can be portable or stationary. Older machines tend to be stationary once they're set up in a scrap yard, they stay there.


This makeup artist turned her frustration into inspiration.
Makeup artist Rocio Cervantes is going viral for her creative way of embracing her acne.
The look features transparent purple star-shaped stickers over her pimples.
Cervantes told INSIDER she hopes people who see the look know that "they are not alone" when it comes to dealing with acne.
Social media is filled with countless makeup tutorials focused on concealing acne, but one makeup artist is going viral for making acne the star of her latest makeup creation.
Rocio Cervantes recently posted a look with transparent purple star stickers surrounding her pimples, and people are loving the creative way she embraced her acne — not to mention the flawless rainbow gradient eye shadow.
Cervantes told INSIDER that she's recently become frustrated with her acne, and she used that frustration to fuel her creativity.
"I've struggled with acne for a really long time, but I also love makeup," Cervantes told INSIDER. "It's my passion, and sometimes my acne can really get in the way of my passion, so I thought why not morph these two together."
"Sometimes my acne can really get in the way of my passion so I thought why not morph these two together," she told INSIDER.
The resulting look quickly went viral, with over 36,000 likes at the time of this post and a retweet from popular beauty guru James Charles. People are calling the photos "beautiful" and "inspiring," and the reaction has taken Cervantes by surprise in the best way possible.
"I was taken back at the response, but it's been so positive and people have been nothing but nice and supportive," Cervantes said. "I've received so many messages from people telling me how it has helped them with their acne so it makes me happy!"
Cervantes hopes that those who come across her inspired look will feel empowered to embrace their acne during those times when it interferes with your self-esteem.
"My advice to those that struggle with acne is that you are beautiful," Cervantes told INSIDER. "I just want people to know they are not alone, they are beautiful, and acne does NOT make anyone ugly."


text:
Radio Sai is the official Radio of the Sri Sathya Sai Media Foundation, disseminating the message and teachings of Sri Sathya Sai Baba. Radio Sai went on air for the first time on November 23, 2001. It was inaugurated by Bhagawan Baba as a channel of the World Space Satellite Radio service. Radio Sai has over the years grown into an Internet Radio streaming service offering six different, nonstop streams – Asia, Afri, Ameri, Telugu, Discourse and Bhajan Stream.
With the Divine Blessings of Bhagwan Sri Sathya Sai Baba, Radio Sai, Karnataka Studio was inaugurated on 24th August 2012 by the respected State President of Karnataka Sri Nagesh G. Dhakappa. With the support of the Radio content team, the studio helps to produce programs which are interesting, informative and cater to all segments of Radio Sai listeners globally. While the studio aims at bring out the hidden talent and tapping into the cultural heritage of Karnataka, by encouraging the various music, folk and theater art forms, the primary intent of all programs is to spread the message of Bhagavan Sri Sathya Sai Baba to every corner of the world.
Special Recent Posts
Ishta Siddhi Vrata at Poornachandra Hall
Chariot reaches Puttaparthi
Pooja to Swami's Chariot for Bike Pilgrimage
With the Grace and Blessings of our Dear Swami, Sai Youth of Karnataka are on a Bike Pilgrimage to P[...]
Aradhana Mahotsav 2018, Bagalkot District
Sairam, On the eve of Sri Sathya Sai Aradhana, in Bagalkot District, 15000 Narayanas were served [...]
Special Class on Fashion Design @ SSSVJ Neelavani, Haliyal, North Kanara
Special class was conducted on 8th April, on fashion design for Shri Sathya Sai Vidya Jyoti Vocatio[...]
Special Projects Events
all events...


Launched in 2015, RWG Mobile has come a long way in offering technology and connectivity services for the Welsh population. Initially launched as a mobile network, RWG now offers technology products and services ranging from apps, mobile network services, security products, hardware and platform as a service ("PaaS"). Through a partnership with SOTI Inc, RWG offers enterprise mobility management solutions for securing, supporting and managing business critical mobile and IOT device deployments remotely which are both network agnostic and work across devices including laptops/PCs, smartphones and tablets, kiosks, POS, signage and AR headsets. www.rwgmobile.wales 01633 415 333.