RAF Coastal Command

RAF Coastal Command was a formation within the Royal Air Force (RAF). It was founded in 1936, when the RAF was restructured into Fighter, Bomber and Coastal commands and played an important role during the Second World War. Maritime Aviation had been neglected in the inter-war period, due to disagreements between the Royal Navy (RN) and RAF over the ownership, roles and investment in maritime air power.

The Admiralty's main concern until 1937 was the return of the Fleet Air Arm to the Royal Navy while the RAF prioritised the development of a bombing force to provide a deterrent. Coastal Command was referred to as the "Cinderella Service" by A V Alexander, the First Lord of the Admiralty in November 1940. Soon after RAF Coastal Area was elevated to Coastal Command, its headquarters moved from Lee-on-Solent to Northwood in northwest London.

During the Second World War, Coastal Command's most important contribution was the protection of Allied convoys from attacks by the German Kriegsmarine'''s U-boats. It also protected Allied shipping from aerial attacks by the Luftwaffe. The main operations of Coastal Command were defensive, defending supply lines in the Battle of the Atlantic, as well as the Mediterranean, Middle East, and African theatres. It operated from bases in the United Kingdom, Iceland, Gibraltar, the Soviet Union, West Africa and North Africa. It also had an offensive capacity, in the North Sea, Arctic, Mediterranean and Baltic, strike wings attacked German shipping carrying war materials from Italy to North Africa and from Scandinavia to Germany.

By 1943 Coastal Command finally received sufficient Very Long Range [VLR] aircraft and its operations proved decisive in the victory over the U-boats. These aircraft were Consolidated B-24 Liberators and from early 1943, these and other Coastal Command aircraft, were fitted with Mark III ASV [air-to-surface vessel] centimetric radar, the latest depth charges, including homing torpedoes, officially classed as Mark 24 mines [nicknamed 'Wandering Annie' or 'Wandering Willie'] and even rockets. The Command saw action from the first day of hostilities until the last day of the Second World War.

Coastal Command completed one million flying hours, 240,000 operations and destroyed 212 U-boats. Coastal Command casualties amounted to 2,060 aircraft to all causes. From 1940 to 1945 Coastal Command sank 366 German transport vessels and damaged 134. The total tonnage sunk was 512,330 tons and another 513,454 tons damaged. 10,663 persons were rescued by the Command, comprising 5,721 Allied crew members, 277 enemy personnel and 4,665 non-aircrews. 5,866 Coastal Command personnel were killed in action. During the Cold War, Coastal Command concentrated on anti-submarine warfare preparations against the fleets of the Warsaw Pact. In 1969, Coastal Command was subsumed into the new Strike Command, which had also absorbed the former Bomber, Fighter and Signals Commands and later absorbed Air Support Command, the former Transport Command.

## Formation and neglect

In 1936, almost 18 years after the end of the First World War, there was a major change in the command structure of the RAF. Several Expansion Schemes were heading at such pace to re-arm the British military in face of the Nazi threat that "Area" formations were now to be called "Commands". Fighter and Bomber Areas became Fighter and Bomber Commands and Coastal Area was renamed Coastal Command. Its headquarters was located at Lee-on-Solent. Air Marshal Sir Arthur Longmore, AOC RAF Coastal Area oversaw the renaming and handed over command to Air Marshal Philip Joubert de la Ferté on 24 August 1936.

In March 1935 the threat from Nazi Germany prompted a series of expansion schemes which pushed the number of squadrons up to 163 (as per Expansion Scheme M, the last before the outbreak of war) and the number of aircraft to 2,549. But it was never fully implemented, and Scheme F, 124 Squadrons and 1,736 aircraft, was the only scheme that ran its full course. It did produce modern aircraft and it made adequate provision for reserves (75 percent), but again, the bomber forces received no less than 50 percent which averaged 57 percent over all schemes. Maritime air units never made up more than 12 per cent of British air strength. From a pre-expansion strength of just five squadrons, four of which were flying boats, the figure of maritime squadrons rose to 18 by September 1939, with a strength of just 176 aircraft. Some 16 of these were allocated to trade defence, but given Trenchard's policy (which was still in place after his retirement) of developing bombers for the maritime arm which could bolster the air offensive, most were not specialised ASW aircraft, and the Air Ministry was thoroughly uninterested in any aircraft which fell outside the bomber function.

De la Ferté was highly critical of the Air Ministry's attitude to his service. In 1937 several exercises were carried out by Coastal Command in co-operation with submarines against the Home Fleet to judge the surface fleet's defence against submarine and air attack. However, despite the experiences of the First World War, no attention was paid to the problem of attacking submarines from the air as part of trade protection measures. Owing to misplaced faith in the imperfect ASDIC invention which was never intended to detect surface-running submarines, it appeared the Royal Navy no longer considered U-boats a threat to Britain's sea lanes. The Air Ministry, keen to concentrate on strategic air forces, did not dispute the Admiralty's conclusions and Coastal Command did not receive any guidance from the Air Ministry. The saving grace for both services was the construction of the Combined Headquarters which enabled rapid collaboration in maritime operations. This was one of the few successes in organisation and preparation made before the outbreak of war.

When the review of the role Coastal Command was to play in war was assessed in 1937, the then AOC Sir Frederick Bowhill was informed by his Senior Air Staff Officer Air Commodore Geoffrey Bromet that the other two commands (Bomber and Fighter) had clear mission objectives while Coastal Command had been given no clear mandate. It was assumed that Coastal Command was to keep sea communications open for merchant shipping and prevent seaborne raids on British coastlines and ports. No mention of U-boats was made by either man. Both apparently assumed aircraft and surface raiders presented the greater threat in British waters, thus following the then Admiralty line that U-boats were no longer a threat. When Admiral Sir Dudley Pound enquired about aerial assets in trade and commerce defence, Chief of the Air Staff Cyril Newall, 1st Baron Newall, replied that there was not enough "jam" [resources] to go around and stated it was more advisable to risk losses on trade routes than weaken the RAF's ability to protect Britain from air attack and bomb its enemies.

In March 1937, the then Director of Operations Group Captain Robert Saundby, complained that the role for Coastal Command in war, namely supporting the bomber offensive, and second, the support of naval forces along the British coastline, were too limited and was in danger of diverting the Command from its main concern: ASW. In October the Deputy Chief of the Air Staff (DCAS) Air Vice Marshal Richard Peirse confirmed that there was no formal role for the service or location of its units. Peirse did reverse the decision to have strategic bombing support as the primary function. This was changed to trade defence. Coastal Command was only to be used for other purposes if trade routes were suffering little interference and the intensity of air attack on Britain, or air attacks on enemy targets, required all available air units for those purposes. However, in December 1937, the Naval and Air Staffs met again and changed the priority to North Sea reconnaissance. The Naval Staff insisted that surface commerce raiders presented the greatest danger, and aircraft could prove decisive only in locating enemy warships. ASW remained in third place, after direct co-operation with surface fleets. In December 1938, this was changed again, and ASW moved up to second priority. In August 1939 it was moved to first priority. When Coastal Command went to war, its first task was to co-operate with the Navy to prevent enemy vessels from escaping into the North Sea and Atlantic Oceans. Secondly, it was to provide ASW support where and when it could. These steps are significant as the language indicates a change from passive reconnaissance of enemy warships and submarines to an active directive which involved the attack of the vessels by Coastal Command aircraft.

Since the late 1920s the tension between the air and naval services had declined. It arose briefly again in 1937 when the question of the FAA operational control arose. On this occasion the British Government sided with the Admiralty. Despite a spirited defence of its asset, once the Minister for Coordination of Defence, Sir Thomas Inskip had decided to transfer the arm, the Air Ministry was content to let the matter rest. Any threat to the Air Ministry's existence had long since passed; budgetary constraint, and the reluctance to engage in another battle which would waste resources were also factors in the Air Ministry's decision not to contest the issue further. However, inter-service squabbling assured maritime aviation's stagnation, especially in shore-based elements. Virtually no co-operation existed in the area of research and development. In the case of Coastal Command, it continued to come third in the Air Ministry's list of priorities, after Fighter and Bomber Commands, well into the late 1930s.

## Second World War

### Early war

From its formation in 1936, Coastal Command did not receive the support it required to be an effective naval air service. In September 1939 Nazi Germany invaded Poland beginning the war in Europe. The Command's position was comfortable for the first nine months of the war, the period known as the Phoney War. German submarines were not able to reach the Atlantic unless they undertook a dangerous transit journey through the North Sea and around Britain's northern waters or through the English Channel, which was guarded by the Royal and French Navies. The powerful French Navy was responsible for covering half of the Atlantic shipping routes and thus contributed half of the Allied forces available.

The events of April to June 1940 overturned the balance of naval and air power, as the Germans conquered Denmark, Norway, The Netherlands, Belgium and France. The occupation of these countries permitted the Luftwaffe and Kriegsmarine to operate from French ports on the Atlantic coast, hundreds of miles closer to the Atlantic shipping lanes. German medium bombers could also reach British ports on the westernmost and northernmost coasts. The advantage enjoyed by the Germans, allowed them to interdict merchant shipping supplying food and war materials to Britain much more effectively, which had the potential to starve Britain. While merchant shipping was suffering these losses, Coastal Command had proven ineffective at countering German air and sea attacks on shipping. But the command could not protect English Channel convoys, and was forced to abandon operations until July 1940. RAF Fighter Command was given the task, supplying air attack and defence with the enemy. Warning signs after the First World War, that U-boats could become a serious threat once again, meant that aircraft would be the best counter to their operations. This fact not being fully understood, Coastal Command became the "Cinderella service" until about 1943.

The situation would not improve until 1942. Coastal Command did operate with effect alongside RAF Bomber Command in disrupting enemy shipping during the Battle of Britain in 1940. Coastal Command attacked shipping and mined waters around invasion ports. The German invasion of Britain in 1940, Operation Sea Lion, was eventually cancelled owing to the German defeat in the Battle of Britain.

During the first three years of the Second World War, Coastal Command and the Admiralty fought a battle with the RAF and Air Ministry over the primacy of trade defence, in relation to the bomber effort against mainland Germany, a strategic tussle which conceivably could have cost the Western Alliance the Battle of the Atlantic. The Air Staff and Bomber Command enjoyed the backing of Churchill and the maritime air effort struggled to receive the recognition it needed. On the outbreak of war, the order of battle listed just 298 aircraft, of which only 171 were operational. On 15 February 1941, Coastal Command was placed under the operational control of the Admiralty. Instrumental in improving the strike rate against submarines was scientific advisor and assistant director of research E. J. Williams, who applied scientific analysis to the logistical problems to great effect. Williams was present at some meetings of the Cabinet Anti-U-boat Committee at 10 Downing Street, under the chairmanship of the Prime Minister.

Owing to the starvation of resources, even as late as March 1943, the Atlantic supply lines were being threatened. This situation arose as a direct result of the lack of very long-range aircraft. Despite the enormous losses of the disastrous 1940–1942 period, known to the Germans as the "First" and "Second Happy Time", the Air Ministry refused to invest in trade defence. Further delays in resource procurement might have led to German success, which could have defeated Britain and forced it out of the war or at least caused a postponement of Operation Torch, the Allied landings in French North-West Africa in 1942 and Operation Overlord, the landing in France, in 1944. Other research indicates that losses unquestionably affected the build-up for Operation Neptune, the naval phase of the landings in Europe.

### Mid and later war

Eventually the Command was given the investment it needed. Radar and long-range aircraft enabled the Command to hunt and destroy U-boats with growing efficiency. German submarines had been sinking a large number of Allied ships in the Atlantic Gap, which was a stretch of water in the central Atlantic beyond the range of most Allied aircraft. The covering of the gap by very-long-range aircraft equipped with radar helped reduce the effectiveness of U-boats. In May 1943 the campaign reached a peak, when a large number of U-boats were sunk with little loss to Allied shipping; Coastal Command had gained the initiative and it was known by the Germans as Black May. Thereafter the suppression of German submarines was effective in the Atlantic and in their transit routes through the Bay of Biscay in 1942, 1943 and 1944. In June 1944 the Normandy landings and subsequent Operation Overlord liberated France and cost the Germans their air and submarine bases won in 1940. The U-boats were forced to relocate to Norway and Germany in August, restoring many of the difficulties faced by the Kriegsmarine in 1939 and early 1940. The entire strategic position, which had been the foundation of the U-boat war since June 1940 had been undermined.

In the last three years of the war, Coastal Command sank more U-boats than any other service and continued to hold the technological advantage from 1943. A brief threat, in the shape of the German Type XXI submarine emerged but was too late to alter the course of the war. Technological answers to the Type XXI were available in the form of 3-centimetre radar and magnetic anomaly detectors in aircraft. At midnight 4 June 1945, official wartime operations ceased. The last mission was flown by Wing Commander J. Barret DFC, commanding officer of No. 201 Squadron RAF. By that time over 2,000 decorations had been awarded. These included four Victoria Crosses, of whom only one survived the war, 17 George Medals, and 82 Distinguished Service Orders.

## Cold War

### Beginnings

The capitulation of Germany in May 1945 was followed by a rapid rundown of Coastal Command with the immediate disbandment of combat units and the transfer of aircraft to the RAF Transport Command. Commonwealth personnel were also sent home and the powerful Bristol Beaufighter and de Havilland Mosquito wings were reduced. The Command still maintained strong air-sea-rescue ASR and reconnaissance forces but its ASW was lopsided. With a few exceptions, only a handful of squadrons with ASW aircraft remained by January 1946.

While the Command retained a minimum peacetime force and the Air Ministry had every intention of maintaining it as such, the fleet was further reduced and suffered from procurement problems. The Short Shetland and Short Seaford were rejected as replacements for the Consolidated B-24 Liberator. A maritime version of the promising Avro Lincoln had yet to be ordered by the time the Lend-Lease programme ended in August 1945. The Short Sunderland was forced to continue as the main operational type until the end of 1946. Most of the aircraft that operated in the command were the Second World War types; the Spitfire, Lancaster, Mosquito and Beaufighter.

The Command was kept busy in the late 1940s. Units were sent to the Middle East and Palestine as part of an air policing policy, in co-operation with the Israeli Air Force and Egyptian Air Force to prevent conflict between the two countries owing to the formation of the state of Israel in 1948. While there, they undertook a major operation, Operation Bobcat, to prevent illegal Jewish migrants coming into Palestine. In May 1948 the variety of aircraft was reduced despite increasing demand for operations. In May, Palestinians began attacking British military installations throughout the region. In the largest British post-war action, Operation Dawn (13 to 14 May 1948) was launched with the support of Coastal Command.

On 28 June 1948 Coastal Command was also involved in the Berlin Airlift. The Soviet Union attempted to cut off all aid to the city which was jointly occupied by the four major powers, the Soviets in the east, and the Americans, French and British in the west. The joint American-British operation continued for almost a year. Coastal Command aircraft were involved as flying boats were the only aircraft with internal anti-corrosion treatment allowing bulk salt to be transported. The Command's operations grew in intensity. By 13 July daily sorties had risen to 16. By October it was 214 sorties (other RAF Commands were also flying in supplies). The flying boats made their flight in using the Elbe river, but these operations came to a close on 14 December 1948, when the hazard from uncharted sandbanks and wreckage which, in some cases had been deliberately placed there by the Soviets to prevent the Western Allies from supplying the city, made operations impractical. Over 1,000 sorties had been made, and 4,500 tons of supplies were flown in and 1,113 people, mainly children, evacuated.

### Soviet threat

NATO, the North Atlantic Treaty Organisation, began preparations for a military defence of Western Europe by incorporating most West European nations into a defence pact against alleged Soviet aggression in April 1951. This led to the militarisation of West Germany in 1955 and was met with the militarisation of East Germany soon after and its merger into the Warsaw Pact alliance with the Soviet Union. The purpose of Coastal Command was to help bolster the defence and guard against a potential Soviet naval threat in Atlantic and European waters. For Coastal Command the main concern was the Atlantic. On 1 March 1950 it had lost the photo reconnaissance units to RAF Bomber Command. The transfer was not complete when North Korea invaded South Korea beginning the Korean War. Handley Page Hastings were hastily modified and ready for operations but were not sent, owing to the need for ASW aircraft in the Eastern Atlantic.

The Avro Shackleton was the main operational aircraft in the 1950s, replacing the wartime Liberator GRs, along with the Neptune MR.1s. At the end of August 1951, No. 201 Squadron RAF became the first unit to complete training on the type. In mid-1953 the order of battle consisted of eight Shackleton squadrons; one at Gibraltar, four covering the South-Western Approaches in the Atlantic and three more covering the North-Western Approaches. This force numbered 64 aircraft. A further four Sunderland squadrons with 20 aircraft were split between the North-Western and South-Western Approaches. The Neptunes, numbering 32 aircraft in four squadrons, covered the North-Eastern and Eastern Approaches. The Helicopter also joined Coastal Command. Bristol Sycamores entered service in 1953 and 16 aircraft were dispersed in Britain for ASW. In March the Avro Lancaster was finally phased out of Coastal Command service.

The Command was too expensive to maintain and cost cuts were made during the 1950s which caused a reduction in strength. By mid-1957 the Command had been cut to 82 aircraft. By mid-1958 it had shrunk to just 67. The Shackletons dominated the core of this force, numbering 54 aircraft. The Neptune was cut from the service altogether, beginning on 31 August 1956. There was little operational action for the Command at this point. It airlifted British Army forces into Egypt during the Suez Crisis which was its major action during this period. The lack of funds and any active conventional military role saw the Command struggle to keep its front-line strength high. There was a brief alert in October 1962, during the Cuban Missile Crisis, when all six squadrons it then possessed were put on high alert, but nothing came of the crisis, although the Shackleton squadrons at RAF Ballykelly were sent to Macrihanish as it was known that Ballykelly was on the Soviet IRBM target list.

In the early 1960s the Soviet Navy and Communist Bloc's fishing fleets began operating around the British Isles in increasing numbers. The British public began taking an interest in their operations as civilian fisherman began complaining about their presence. Operation Chacewater began, in which Coastal Command began monitoring their movements, in particular other vessels that loitered in areas covering the arrival and departure routes for Royal Navy nuclear submarine forces. Soon after, counter operations such as Operation Adjutant were carried out, which was aimed at searching for Soviet submarines. The main threat from the Soviets in the Atlantic came from the Soviet Northern Fleet and in early 1965 most of the Command's units were concentrated in No. 18 Group RAF, based in Scotland to monitor their activities. No recorded confrontation took place between Coastal Command and Soviet naval forces during this time, although both the Shackletons from RAF Ballykelly and frigates from Londonderry would 'ping' the Soviet submarines carrying out surveillance off the mouth of Lough Foyle. In at least one instance, a Ballykelly-based Shackleton lost its radome when making a mock attack on the Russian sub.

In 1969 the special-purpose Hawker-Siddeley Nimrod, based on the de Havilland Comet airliner, was introduced into RAF service and Coastal Command duties were passed on to general squadrons. The Nimrod was a replacement for the Shackleton and it began to do so on 2 October 1969. Less than eight weeks later, Coastal Command was disbanded and ceased to exist on 27 November 1969, when it was subsumed into RAF Strike Command.

## Organisation

## Commanders in Chief

The following officers commanded the service:

## Depiction in film

The work of Coastal Command was immortalised in a 1942 wartime propaganda documentary named Coastal Command'' with a score by Ralph Vaughan Williams.

## See also

- List of Royal Air Force commands

Royal Air Force formation (1936–1969)

1936 establishments in the United Kingdom

1969 disestablishments in the United Kingdom

Military units and formations disestablished in 1969

Military units and formations established in 1936

Military units and formations in Hertfordshire


Nucleon magnetic moment

The nucleon magnetic moments are the intrinsic magnetic dipole moments of the proton and neutron, symbols μp and μn. The nucleus of an atom comprises protons and neutrons, both nucleons that behave as small magnets. Their magnetic strengths are measured by their magnetic moments. The nucleons interact with normal matter through either the nuclear force or their magnetic moments, with the charged proton also interacting by the Coulomb force.

The proton's magnetic moment, surprisingly large, was directly measured in 1933 by Otto Stern team in University of Hamburg. While the neutron was determined to have a magnetic moment by indirect methods in the mid 1930s. Luis Alvarez and Felix Bloch made the first accurate, direct measurement of the neutron's magnetic moment in 1940. The proton's magnetic moment is exploited to make measurements of molecules by proton nuclear magnetic resonance. The neutron's magnetic moment is exploited to probe the atomic structure of materials using scattering methods and to manipulate the properties of neutron beams in particle accelerators.

The existence of the neutron's magnetic moment and the large value for the proton magnetic moment indicate that nucleons are not elementary particles. For an elementary particle to have an intrinsic magnetic moment, it must have both spin and electric charge. The nucleons have spin ħ/2, but the neutron has no net charge. Their magnetic moments were puzzling and defied a valid explanation until the quark model for hadron particles was developed in the 1960s. The nucleons are composed of three quarks, and the magnetic moments of these elementary particles combine to give the nucleons their magnetic moments.

## Description

The CODATA recommended value for the magnetic moment of the proton is or The best available measurement for the value of the magnetic moment of the neutron is Here, μN is the nuclear magneton, a standard unit for the magnetic moments of nuclear components, and μB is the Bohr magneton, both being physical constants. In SI units, these values are and A magnetic moment is a vector quantity, and the direction of the nucleon's magnetic moment is determined by its spin. The torque on the neutron that results from an external magnetic field is towards aligning the neutron's spin vector opposite to the magnetic field vector.

The nuclear magneton is the spin magnetic moment of a Dirac particle, a charged, spin-1/2 elementary particle, with a proton's mass mp, in which anomalous corrections are ignored. The nuclear magneton is $\mu_\text{N} = \frac{e \hbar}{2 m_\text{p}},$ where e is the elementary charge, and ħ is the reduced Planck constant. The magnetic moment of such a particle is parallel to its spin. Since the neutron has no charge, it should have no magnetic moment by the analogous expression. The non-zero magnetic moment of the neutron thus indicates that it is not an elementary particle. The sign of the neutron's magnetic moment is that of a negatively charged particle. Similarly, that the magnetic moment of the proton, is not almost equal to 1 μN indicates that it too is not an elementary particle. Protons and neutrons are composed of quarks, and the magnetic moments of the quarks can be used to compute the magnetic moments of the nucleons.

Although the nucleons interact with normal matter through magnetic forces, the magnetic interactions are many orders of magnitude weaker than the nuclear interactions. The influence of the neutron's magnetic moment is therefore only apparent for low energy, or slow, neutrons. Because the value for the magnetic moment is inversely proportional to particle mass, the nuclear magneton is about 1/2000 as large as the Bohr magneton. The magnetic moment of the electron is therefore about 1000 times larger than that of the nucleons.

The magnetic moments of the antiproton and antineutron have the same magnitudes as their antiparticles, the proton and neutron, but they have opposite sign.

## Measurement

### Proton

The magnetic moment of the proton was discovered in 1933 by Otto Stern, Otto Robert Frisch and Immanuel Estermann at the University of Hamburg. The proton's magnetic moment was determined by measuring the deflection of a beam of molecular hydrogen by a magnetic field. Stern won the Nobel Prize in Physics in 1943 for this discovery.

### Neutron

The neutron was discovered in 1932, and since it had no charge, it was assumed to have no magnetic moment. Indirect evidence suggested that the neutron had a non-zero value for its magnetic moment, however, until direct measurements of the neutron's magnetic moment in 1940 resolved the issue.

Values for the magnetic moment of the neutron were independently determined by R. Bacher at the University of Michigan at Ann Arbor (1933) and I. Y. Tamm and S. A. Altshuler in the Soviet Union (1934) from studies of the hyperfine structure of atomic spectra. Although Tamm and Altshuler's estimate had the correct sign and order of magnitude (μn = −0.5 μN), the result was met with skepticism.

By 1934 groups led by Stern, now at the Carnegie Institute of Technology in Pittsburgh, and I. I. Rabi at Columbia University in New York had independently measured the magnetic moments of the proton and deuteron. The measured values for these particles were only in rough agreement between the groups, but the Rabi group confirmed the earlier Stern measurements that the magnetic moment for the proton was unexpectedly large. Since a deuteron is composed of a proton and a neutron with aligned spins, the neutron's magnetic moment could be inferred by subtracting the deuteron and proton magnetic moments. The resulting value was not zero and had a sign opposite to that of the proton. By the late 1930s, accurate values for the magnetic moment of the neutron had been deduced by the Rabi group using measurements employing newly developed nuclear magnetic resonance techniques.

The value for the neutron's magnetic moment was first directly measured by L. Alvarez and F. Bloch at the University of California at Berkeley in 1940. Using an extension of the magnetic resonance methods developed by Rabi, Alvarez and Bloch determined the magnetic moment of the neutron to be μn = −1.93(2) μN. By directly measuring the magnetic moment of free neutrons, or individual neutrons free of the nucleus, Alvarez and Bloch resolved all doubts and ambiguities about this anomalous property of neutrons.

### Unexpected consequences

The large value for the proton's magnetic moment and the inferred negative value for the neutron's magnetic moment were unexpected and could not be explained. The unexpected values for the magnetic moments of the nucleons would remain a puzzle until the quark model was developed in the 1960s.

The refinement and evolution of the Rabi measurements led to the discovery in 1939 that the deuteron also possessed an electric quadrupole moment. This electrical property of the deuteron had been interfering with the measurements by the Rabi group. The discovery meant that the physical shape of the deuteron was not symmetric, which provided valuable insight into the nature of the nuclear force binding nucleons. Rabi was awarded the Nobel Prize in 1944 for his resonance method for recording the magnetic properties of atomic nuclei.

## Nucleon gyromagnetic ratios

The magnetic moment of a nucleon is sometimes expressed in terms of its g-factor, a dimensionless scalar. The convention defining the g-factor for composite particles, such as the neutron or proton, is $\boldsymbol{\mu} = \frac{g \mu_\text{N}}{\hbar} \boldsymbol{I},$ where μ is the intrinsic magnetic moment, I is the spin angular momentum, and g is the effective g-factor. While the g-factor is dimensionless, for composite particles it is defined relative to the nuclear magneton. For the neutron, I is 1/2 ħ, so the neutron's g-factor is while the proton's g-factor is

The gyromagnetic ratio, symbol γ, of a particle or system is the ratio of its magnetic moment to its spin angular momentum, or $\boldsymbol{\mu} = \gamma \boldsymbol{I}.$

For nucleons, the ratio is conventionally written in terms of the proton mass and charge, by the formula

$\gamma = \frac{g \mu_\text{N}}{\hbar} = g \frac{e}{2m_\text{p}}.$

The neutron's gyromagnetic ratio is The proton's gyromagnetic ratio is The gyromagnetic ratio is also the ratio between the observed angular frequency of Larmor precession and the strength of the magnetic field in nuclear magnetic resonance applications, such as in MRI imaging. For this reason, the quantity γ/2π with the unit MHz/T is often given. The quantities γn/(2π) = −29.1646931(69) MHz/T and γp/(2π) = 42.5774806(10) MHz⋅T−1, called "gamma bar", are therefore convenient.

## Physical significance

### Larmor precession

When a nucleon is put into a magnetic field produced by an external source, it is subject to a torque tending to orient its magnetic moment parallel to the field (in the case of the neutron, its spin is antiparallel to the field). As with any magnet, this torque is proportional the product of the magnetic moment and the external magnetic field strength. Since the nucleons have spin angular momentum, this torque will cause them to precess with a well-defined frequency, called the Larmor frequency. It is this phenomenon that enables the measurement of nuclear properties through nuclear magnetic resonance. The Larmor frequency can be determined from the product of the gyromagnetic ratio with the magnetic field strength. Since for the neutron the sign of γn is negative, the neutron's spin angular momentum precesses counterclockwise about the direction of the external magnetic field.

### Proton nuclear magnetic resonance

Nuclear magnetic resonance employing the magnetic moments of protons is used for nuclear magnetic resonance (NMR) spectroscopy. Since hydrogen-1 nuclei are within the molecules of many substances, NMR can determine the structure of those molecules.

### Determination of neutron spin

The interaction of the neutron's magnetic moment with an external magnetic field was exploited to determine the spin of the neutron. In 1949, D. Hughes and M. Burgy measured neutrons reflected from a ferromagnetic mirror and found that the angular distribution of the reflections was consistent with spin 1/2. In 1954, J. Sherwood, T. Stephenson, and S. Bernstein employed neutrons in a Stern–Gerlach experiment that used a magnetic field to separate the neutron spin states. They recorded the two such spin states, consistent with a spin 1/2 particle. Until these measurements, the possibility that the neutron was a spin 3/2 particle could not have been ruled out.

### Neutrons used to probe material properties

Since neutrons are neutral particles, they do not have to overcome Coulomb repulsion as they approach charged targets, unlike protons and alpha particles. Neutrons can deeply penetrate matter. The magnetic moment of the neutron has therefore been exploited to probe the properties of matter using scattering or diffraction techniques. These methods provide information that is complementary to X-ray spectroscopy. In particular, the magnetic moment of the neutron is used to determine magnetic properties of materials at length scales of 1–100 Å using cold or thermal neutrons. B. Brockhouse and C. Shull won the Nobel Prize in physics in 1994 for developing these scattering techniques.

### Control of neutron beams by magnetism

Without an electric charge, neutron beams cannot be controlled by the conventional electromagnetic methods employed for particle accelerators. The magnetic moment of the neutron allows some control of neutrons using magnetic fields, however, including the formation of polarized neutron beams. One technique employs the fact that cold neutrons will reflect from some magnetic materials at great efficiency when scattered at small grazing angles. The reflection preferentially selects particular spin states, thus polarizing the neutrons. Neutron magnetic mirrors and guides use this total internal reflection phenomenon to control beams of slow neutrons.

### Nuclear magnetic moments

Since an atomic nucleus consists of a bound state of protons and neutrons, the magnetic moments of the nucleons contribute to the nuclear magnetic moment, or the magnetic moment for the nucleus as a whole. The nuclear magnetic moment also includes contributions from the orbital motion of the charged protons. The deuteron, consisting of a proton and a neutron, has the simplest example of a nuclear magnetic moment. The sum of the proton and neutron magnetic moments gives 0.879 μN, which is within 3% of the measured value 0.857 μN. In this calculation, the spins of the nucleons are aligned, but their magnetic moments offset because of the neutron's negative magnetic moment.

## Nature of the nucleon magnetic moments

A magnetic dipole moment can be generated by two possible mechanisms. One way is by a small loop of electric current, called an "Ampèrian" magnetic dipole. Another way is by a pair of magnetic monopoles of opposite magnetic charge, bound together in some way, called a "Gilbertian" magnetic dipole. Elementary magnetic monopoles remain hypothetical and unobserved, however. Throughout the 1930s and 1940s it was not readily apparent which of these two mechanisms caused the nucleon intrinsic magnetic moments. In 1930, Enrico Fermi showed that the magnetic moments of nuclei (including the proton) are Ampèrian. The two kinds of magnetic moments experience different forces in a magnetic field. Based on Fermi's arguments, the intrinsic magnetic moments of elementary particles, including the nucleons, have been shown to be Ampèrian. The arguments are based on basic electromagnetism, elementary quantum mechanics, and the hyperfine structure of atomic s-state energy levels. In the case of the neutron, the theoretical possibilities were resolved by laboratory measurements of the scattering of slow neutrons from ferromagnetic materials in 1951.

## Anomalous magnetic moments and meson physics

The anomalous values for the magnetic moments of the nucleons presented a theoretical quandary for the 30 years from the time of their discovery in the early 1930s to the development of the quark model in the 1960s. Considerable theoretical efforts were expended in trying to understand the origins of these magnetic moments, but the failures of these theories were glaring. Much of the theoretical focus was on developing a nuclear-force equivalence to the remarkably successful theory explaining the small anomalous magnetic moment of the electron.

The problem of the origins of the magnetic moments of nucleons was recognized as early as 1935. G. C. Wick suggested that the magnetic moments could be caused by the quantum-mechanical fluctuations of these particles in accordance with Fermi's 1934 theory of beta decay. By this theory, a neutron is partly, regularly and briefly, disassociated into a proton, an electron, and a neutrino as a natural consequence of beta decay. By this idea, the magnetic moment of the neutron was caused by the fleeting existence of the large magnetic moment of the electron in the course of these quantum-mechanical fluctuations, the value of the magnetic moment determined by the length of time the virtual electron was in existence. The theory proved to be untenable, however, when H. Bethe and R. Bacher showed that it predicted values for the magnetic moment that were either much too small or much too large, depending on speculative assumptions.

Similar considerations for the electron proved to be much more successful. In quantum electrodynamics (QED), the anomalous magnetic moment of a particle stems from the small contributions of quantum mechanical fluctuations to the magnetic moment of that particle. The g-factor for a "Dirac" magnetic moment is predicted to be g = −2 for a negatively charged, spin-1/2 particle. For particles such as the electron, this "classical" result differs from the observed value by around 0.1%; the difference compared to the classical value is the anomalous magnetic moment. The g-factor for the electron is measured to be QED is the theory of the mediation of the electromagnetic force by photons. The physical picture is that the effective magnetic moment of the electron results from the contributions of the "bare" electron, which is the Dirac particle, and the cloud of "virtual", short-lived electron–positron pairs and photons that surround this particle as a consequence of QED. The effects of these quantum mechanical fluctuations can be computed theoretically using Feynman diagrams with loops.

The one-loop contribution to the anomalous magnetic moment of the electron, corresponding to the first-order and largest correction in QED, is found by calculating the vertex function shown in the diagram on the right. The calculation was discovered by J. Schwinger in 1948. Computed to fourth order, the QED prediction for the electron's anomalous magnetic moment agrees with the experimentally measured value to more than 10 significant figures, making the magnetic moment of the electron one of the most accurately verified predictions in the history of physics.

Compared to the electron, the anomalous magnetic moments of the nucleons are enormous. The g-factor for the proton is 5.6, and the chargeless neutron, which should have no magnetic moment at all, has a g-factor of −3.8. Note, however, that the anomalous magnetic moments of the nucleons, that is, their magnetic moments with the expected Dirac particle magnetic moments subtracted, are roughly equal but of opposite sign: μp − 1.00 μN = +1.79 μN, but μn − 0.00 μN = −1.91 μN.

The Yukawa interaction for nucleons was discovered in the mid-1930s, and this nuclear force is mediated by pion mesons. In parallel with the theory for the electron, the hypothesis was that higher-order loops involving nucleons and pions may generate the anomalous magnetic moments of the nucleons. The physical picture was that the effective magnetic moment of the neutron arose from the combined contributions of the "bare" neutron, which is zero, and the cloud of "virtual" pions and photons that surround this particle as a consequence of the nuclear and electromagnetic forces. The Feynman diagram at right is roughly the first-order diagram, with the role of the virtual particles played by pions. As noted by A. Pais, "between late 1948 and the middle of 1949 at least six papers appeared reporting on second-order calculations of nucleon moments". These theories were also, as noted by Pais, "a flop" –  they gave results that grossly disagreed with observation. Nevertheless, serious efforts continued along these lines for the next couple of decades, to little success. These theoretical approaches were incorrect because the nucleons are composite particles with their magnetic moments arising from their elementary components, quarks.

## Quark model of nucleon magnetic moments

In the quark model for hadrons, the neutron is composed of one up quark (charge ++ 2 /3 e) and two down quarks (charge −+ 1 /3 e) while the proton is composed of one down quark (charge −+ 1 /3 e) and two up quarks (charge ++ 2 /3 e). The magnetic moment of the nucleons can be modeled as a sum of the magnetic moments of the constituent quarks, although this simple model belies the complexities of the Standard Model of Particle Physics. The calculation assumes that the quarks behave like pointlike Dirac particles, each having their own magnetic moment, as computed using an expression similar to the one above for the nuclear magneton: $\ \mu_\text{q} = \frac{\ e_\text{q} \hbar\ }{2 m_\text{q}}\ ,$ where the q-subscripted variables refer to quark magnetic moment, charge, or mass. Simplistically, the magnetic moment of a nucleon can be viewed as resulting from the vector sum of the three quark magnetic moments, plus the orbital magnetic moments caused by the movement of the three charged quarks within it.

In one of the early successes of the Standard Model (SU(6) theory), in 1964 M. Beg, B. Lee, and A. Pais theoretically calculated the ratio of proton-to-neutron magnetic moments to be −+3/ 2 , which agrees with the experimental value to within 3%. The measured value for this ratio is −1.45989806(34). A contradiction of the quantum mechanical basis of this calculation with the Pauli exclusion principle led to the discovery of the color charge for quarks by O. Greenberg in 1964.

From the nonrelativistic quantum-mechanical wave function for baryons composed of three quarks, a straightforward calculation gives fairly accurate estimates for the magnetic moments of neutrons, protons, and other baryons. For a neutron, the magnetic moment is given by μn =  4 /3 μd −  1 /3 μu , where μd and μu are the magnetic moments for the down and up quarks respectively. This result combines the intrinsic magnetic moments of the quarks with their orbital magnetic moments and assumes that the three quarks are in a particular, dominant quantum state.

The results of this calculation are encouraging, but the masses of the up or down quarks were assumed to be  1 /3 the mass of a nucleon. The masses of the quarks are actually only about 1% that of a nucleon. The discrepancy stems from the complexity of the Standard Model for nucleons, where most of their mass originates in the gluon fields, virtual particles, and their associated energy that are essential aspects of the strong force. Furthermore, the complex system of quarks and gluons that constitute a nucleon requires a relativistic treatment. Nucleon magnetic moments have been successfully computed from first principles, requiring significant computing resources.

## See also

- Neutron triple-axis spectrometry
- LARMOR neutron microscope
- Neutron electric dipole moment
- Aharonov–Casher effect

In physics, proton and neutron magnetism


The Darkness II

The Darkness II is a 2012 first-person shooter video game developed by Digital Extremes and published by 2K. The game is the sequel to The Darkness (2007) and based on the comic book series published by Top Cow Productions. The player controls Jackie Estacado, a mafia hitman who possesses a mysterious power called "the Darkness" that grants him supernatural abilities and a pair of Demon Arms. The game features elements found in role-playing video games such as skill trees, experience, and a four-player cooperative mode. The player must rescue the soul of Jackie's dead girlfriend, which was trapped by the Darkness in Hell, and confront the Brotherhood, a group of armed cultists trying to take the Darkness away from Jackie.

Digital Extremes replaced the first game's developer Starbreeze Studios, though Paul Jenkins returned to write the script for the sequel. While the main narrative was envisioned to be a personal journey for Jackie, developers described the cooperative multiplayer mode as a "dark comedy". Singer Mike Patton returned to voice the Darkness, and Brian Bloom provided the voice for Jackie Estacado, replacing Kirk Acevedo. The development artists hand-painted the majority of the game's assets to create a comic book-influenced visual style.

The Darkness II was released for Windows, PlayStation 3, and Xbox 360 in February 2012. The game received positive reviews upon release, with critics praising the gameplay, story, pacing, and art style. Criticisms were directed at the game's short length, technical issues, and lack of replay value. The game debuted as the third best-selling game in its first week of release in the United Kingdom.

## Gameplay

Jackie can use various firearms, such as submachine guns, shotguns, and assault rifles, and has the ability to dual wield some of these weapons. Additionally, he is armed with a pair of Demon Arms, which resemble tentacles and can be used to slash enemies or pick up various items within the environment (parking meters, car doors, etc.) to use as projectile weapons or shields. The Demon Arms can rip out the heart of fallen enemies and devour them for health, pick up enemies for execution, or throw them. The player is guided by a Darkling, a goblin-like creature that assists in combat and gathers weapons and ammo. At several points, the player can directly control the Darkling, allowing them to squeeze into tight spaces that Jackie cannot enter and execute enemies from behind. When exposed to light, Jackie's health regeneration and Darkness abilities are disabled. In addition, his vision will become blurred and he will experience a ringing sound when exposed. The player can disable these sources by shooting them, causing them to malfunction.

The game features elements found in role-playing video games. Killing enemies, devouring hearts and performing executions earn the player Essence, which can be used to purchase upgrades at various talent shrines. Collecting relics, which serve as collectibles, earns a small amount of Essence. The skill tree is divided into four main aspects: Hitman, Execution, Darkness Powers, and Demon Arm. The Hitman aspect consists of passive upgrades that improve the weapon's reload time and magazine size. The Execution tree allows each execution to net more benefits, such as gaining a massive amount of health, ammo or a shield. Darkness Powers and the Demon Arms grant players access to active abilities, some of which have a brief cooldown after use. These abilities include Gun Channeling, an ability that gives the player unlimited ammo and enhanced damage for a short time; Swarm, which distracts enemies; and Black Hole, which triggers a large area of effect attack that sucks enemies into a vortex.

The game features a cooperative multiplayer campaign called "Vendettas" that runs parallel to the main campaign and allows up to four players to play together. The story involves four hitmen working for Jackie as they attempt to stop the Brotherhood from obtaining the Spear of Destiny. Each character has different Darkness powers and is armed with a unique special weapon. For instance, Inugami is a character who uses a Darkness-infused samurai sword, while Shoshanna uses a blunderbuss which can shoot without bullets. Although the mode can be played solo, the experience is significantly more difficult. There is an arcade mode called "Hit List" that allows players to replay certain Vendetta missions and complete challenges.

## Plot

Jackie Estacado (Brian Bloom) has become head of the Franchetti family, and has learned to suppress the Darkness (Mike Patton), an ancient demonic force in his bloodline. Jackie is haunted by the memory of his murdered girlfriend, Jenny Romano (Stephanie Frame). Jackie and his crew are attacked in a restaurant by a rival gang. Wounded, Jackie restores his powers using the Darkness. Aided by the Darkling (Peter Newman)—a goblin-like familiar—Jackie pursues his attackers into the subway. A vision of Jenny appears, then Jackie is apparently hit by a train. Jackie seemingly awakens to find himself in a mental institution, where various members of his crew are patients and staff. Among them is estranged occultist Johnny Powell, who tells Jackie to find him.

Reawakening with his men, Jackie plans a counterattack. Jimmy the Grape (Frank Ashmore), provides a lead that points to Swifty, a crime boss. Swifty is subdued; he explains that a shady group at the Brimstone Club brothel paid him to put the hit on Jackie. The Darkness murders Swifty to silence him. Vinnie (Rick Pasqualone) enlists his contact at Brimstone to help them. At the club, Jackie encounters armed cultists of the Brotherhood, a secret society who ordered the hit and wish to use the Darkness for themselves. They ambush Jackie with blinding lights that inhibit the Darkness, and Jackie is knocked out. Waking up, he finds himself crucified and a device (the Siphon) draining his dark power. He is greeted by Victor (William Salyers) who offers to take the Darkness from him in exchange for the lives of his family. Refusing, he loses consciousness and finds himself in Hell where the Darkness keeps Jenny's soul.

Jackie breaks free but Victor threatens to murder Jackie's Aunt Sarah (Bridger Fox). As the club burns, the Darkness offers Jenny's soul in exchange for the Siphon. Jackie and his men retake the penthouse, but Jackie is shot by Bragg, a Brotherhood enforcer, who murders Sarah. Jackie awakens in a psychiatric ward where Jenny and his crew are staff and patients. They tell him that his mob stories are delusions. At Sarah's funeral, the Brotherhood launches another attack. Jackie subdues Bragg, who says Victor is based in an abandoned theme park. Victor shuts Jackie in an iron maiden; he loses consciousness. Again, he wakes in the ward, but the janitor (his Darkling) explains that the asylum is a trap to keep him away from Jenny.

Victor drains the Darkness from Jackie. The Darkling helps Jackie escape and retake a small portion of the Darkness. Jackie pursues Victor through a mansion once owned by Carlo Estacado, Jackie's father. Jackie learns from Victor that Carlo had promised the Darkness to the Brotherhood to keep Jackie free. Jackie kills Victor and impales himself with the Siphon, regaining the Darkness and killing himself to rescue Jenny from Hell. Jackie once again wakes up in the psychiatric ward where the staff offer to take him to Jenny. The Darkling sacrifices himself to help Jackie escape. Jackie is confronted by Victor, Jenny, and an orderly who attempt to convince Jackie that his life as a mob boss is a delusion.

On the roof, the player is given a choice to stay with Jenny in the ward, or reject the asylum and attempt to reach Hell. If the player chooses to stay, Jenny and Jackie slow dance, and the game ends. Otherwise, Jackie jumps from the roof and falls into Hell. The Darkness sends demons to stop Jackie, but Jackie releases Jenny from her bindings and the couple embraces. In a post-credits scene, Jenny is revealed to have become the new host for the Angelus, who has seen the destruction Jackie and the Darkness have caused. Jackie is too powerful and must remain trapped in Hell; leaving him screaming as the screen fades.

## Development

Publisher 2K Games approached Canadian developer Digital Extremes to develop The Darkness II, replacing Starbreeze Studios which worked on the first game. Digital Extremes worked on the title for three years. Paul Jenkins returning as the title's writer. According to Starbreeze's CEO Mikael Nermark, the company was not given the option of working on the sequel and was already busy working on Syndicate when The Darkness II was announced.

According to director Sheldon Carter, Digital Extremes agreed to assume development responsibilities as the team wanted to create a shooter with a large emphasis on the story. Both Jenkins and the team at Digital Extremes worked closely, with the team making adjustments to Jenkins' script to suit the gameplay. Carter called the narrative a "love story", which he felt "[balanced] the adrenaline of the action", while the first part of the game's three-act plot was about "survival" since Jackie was attacked by an opposing mob. The team spent a lot of time working on the tone of Jackie. Carter compared Jackie to Tony Soprano, a "badass" character who has to face a lot of internal struggles. The team hoped that the story could make the players sympathize with Jackie. According to designer Tom Galt, while Jackie was a mob boss on the surface, "in his heart he is human and a good-natured guy". With the game's large focus on narrative, the Darkling was given a personality and played a huge role in the story. The game does not cut to third-person so that a limited extent of control can be granted to players even in cinematics. While the game has a heavy narrative focus, all cutscenes and cinematics can be skipped for players who only want to enjoy the gameplay. One of the biggest requests from players of the first game was to have Mike Patton return to voice the Darkness. Nolan North served as a stand-in voice actor for Jackie during the game's pre-production, before Brian Bloom was chosen to voice the character.

The Darkness comic was a large inspiration for the team. The team read the comic and decided to adopt a comic book-influenced "graphic noir" art style, as they believed the comic's use of high contrast colors contributed to its success. The team used some of the assets made by Starbreeze as a reference, and created new ones using their own internal proprietary game engine named the Evolution Engine, which powered the studio's previous game Dark Sector (2008). The development artists hand-painted the majority of the game's assets, though this idea was initially met with resistance within the art team due to the huge amount of workload such an approach would create.

The team decided to make the title more action-orientated in an attempt to differentiate itself from its predecessor. The shooting mechanic was refined, and the concept of "quad-wielding", which allows players to engage in combat using both the Demon Arms and duel-wielding weapons, was introduced. Carter explained that they saw the Demon Arms as an opportunity to make the combat more "up close and personal". The team changed the game's abilities to supplement this, such as turning the ability of Black Hole into a random drop from enemies. The quad-wielding mechanic enabled the combat to have more variety, allowing players to approach the same scenario with different combat styles and encourages players to experiment with different tactics. The gameplay was designed to be violent, with some execution animations being removed for being not "extravagant" enough. To ensure the game was not too easy, the team disabled Jackie's powers when he is exposed to light and created various enemy types to challenge the player in different ways.

The game's cooperative mode Vendetta features a story that runs parallel to the game's main narrative. The team envisioned Vendetta as a dark comedy with over-the-top characters. It is tonally very different from the main game, and the team hoped that players would use the Vendetta mode to "blow off some steam" after experiencing Jackie's story in the main narrative. The team used the mode to explore other characters and elements in the universe, and Jenkins has written more than 10 pages of backstory for each of the four playable characters.

2K unveiled the game in May 2011. The game was initially set to be released in October the same year, but was delayed until February 2012. Players who pre-ordered the game would have upgraded to the Limited Edition, which included gameplay bonuses, illustration drawn by Marc Silvestri, and digital download for The Darkness Origins Volume 1 and Volume 2. 2K provided extensive marketing for the game, launching a four-week promotion program on Kerrang Radio, partnering with Forbidden Planet for window displays and in-store promotions, and placing TV advertisements on both SyFy and Horror Channel. A demo for the game was released in January 2012 on Steam, Xbox Live Arcade and PlayStation Network.

## Reception

The game received generally positive reviews from critics upon release, according to review aggregator Metacritic. It was the third best-selling retail game in its week of release in the UK, surpassed by Kingdoms of Amalur: Reckoning and Final Fantasy XIII-2.

The story received critical acclaim from players. Mikel Reparaz from GamesRadar described the narrative as "part mob drama, part surreal comedy, and part supernatural revenge romance", though he disliked the cliffhanger ending. While the game focuses on the relationship between Jackie and Jenny, Reparaz noted that the supporting characters were "endearing", and remarked that they were well-written and well-acted. He stated he liked the combinations of gun-play and Demon Arms gameplay, which he felt turned Jackie into "an unstoppable dynamo of horror". He also enjoyed the execution animations, which he felt were "brutal" and "never quite get old", though he felt that the gun-play became repetitive by the end of the game. Anthony Gallegos from IGN felt that the story was not as immediately interesting as the first game and noted that it reused some of its predecessors' plot devices, but remarked that some of the scenes with Jenny were "touching", which made the story more "personal" for the player. He further commented that the game's story focus enabled the title to have better pacing. Rich McCormick from PC Gamer praised the story for being "involving", and that the title "plays with concepts of unreliable narration in a way that only games allow". Conrad Zimmerman from Destructoid felt the narrative was fairly average, but the game's storytelling was "handled remarkably well". Andrew Reiner from Game Informer remarked that unlike the original game, the title is more of a fast-paced shooter than a supernatural thriller, and he felt that the story and the characters were inferior when compared to the first game. Kevin VanOrd from GameSpot praised the character development and the game's pacing. He described the story as "unusual" and "creepy", and added that the game's narrative excels when it "plays with your expectations and has you wondering".

The gameplay received a positive response from critics. Daniel Bischoff from Game Revolution called the gun-play "responsive" and the Demon Arms "fun to control". He particularly liked the combat variety and enemy types, which put the players in various combat scenarios, but was disappointed by the game's length, which lasted for only seven hours. Zimmerman agreed that the game was short, but said the title was fun throughout. Dan Whitehead from Eurogamer also praised the Demon Arms and added that it helped "opening up combat possibilities that other shooters can't hope to compete with". He further praised the developer for making the combat faster and refining the gameplay of the original. Gallegos praised the combat for being "vastly superior" to the first game and said that Jackie's overpowered nature made the game more exciting as players could focus on fun ways to kill enemies. He also liked the skill trees, which he felt have reinvigorated the combat during the later sections of the game. McCormick noted that the game's control was not too overwhelming for players despite needing to control multiple limbs at once. He was disappointed by the final levels, which he felt was a "slog" to play through. Reiner praised the game for making players feel powerful, but he felt that the game was repetitive due to the lack of combat variety and remarked that combat "relies on reflexes more than strategy". Most reviewers thought that the cooperative multiplayer mode was fun and that it provided extra gameplay for an otherwise short title, though both Ben Gilbert from Joystiq and Zimmerman thought the combat not as exciting as the main game since the playable characters in the Vendetta mode do not have Demon Arms. Whitehead noted that the mode was "basic to the point of being crude", though he felt the secondary story was "enjoyable".

The game's presentation received mixed reviews. Gilbert praised the art direction, calling it "gorgeous" and "impressive". Zimmerman liked the cel-shaded graphics, which he felt was "evocative of the comic books from which these games originate" and made the game "surprisingly easy to get sucked in". Reiner, however, felt that the new art style did not capture the eerie feeling of the original game. Gallegos noted that the reviewed copy suffered from software bugs, broken animations, glitches, and frame rate issues and felt that the game was marred by polish issues.

2012 first-person shooter game

Multiplayer and single-player video games

Video games based on Top Cow Productions


Domestic sheep reproduction

Domestic sheep reproduce sexually much like other mammals, and their reproductive strategy is furthermore very similar to other domestic herd animals. A flock of sheep is generally mated by a single ram, which has either been chosen by a farmer or has established dominance through physical contest with other rams (in feral populations). Most sheep have a breeding season (tupping) in the autumn, though some are able to breed year-round.

Largely as a result of the influence of humans in sheep breeding, ewes often produce multiple lambs. This increase in the lamb births, both in number and birth weight, may cause problems in delivery and lamb survival, requiring the intervention of shepherds.

## Sexual behavior

Ewes generally reach sexual maturity at six to eight months of age, and rams generally at four to six (ram lambs have occasionally been known to impregnate their mothers at two months). Sheep are seasonally polyoestrus animals. Ewes enter into oestrus cycles about every 17 days, which last for approximately 30 hours. In addition to emitting a scent, they indicate readiness through physical displays towards rams. The phenomenon of the freemartin, a female bovine that is behaviorally masculine and lacks functioning ovaries, is commonly associated with cattle, but does occur to some extent in sheep. The instance of freemartins in sheep may be increasing in concert with the rise in twinning (freemartins are the result of male-female twin combinations). The Flehmen response is exhibited by rams when they smell the urine of a ewe in oestrous. The vomeronasal organ has receptors which detect the oestrogens in the ewe's urine. The ram displays this by extending his neck and curling his lip.

### Rutting

Without human intervention, rams may fight during the rut to determine which individuals may mate with ewes. Rams, especially unfamiliar ones, will also fight outside the breeding period to establish dominance; rams can kill one another if allowed to mix freely. During the rut, even normally friendly rams may become aggressive towards humans due to increases in their hormone levels.

Historically, especially aggressive rams were sometimes blindfolded or hobbled. Today, those who keep rams typically prefer softer preventative measures, such as moving within a clear line to an exit, never turning their back on a ram, and possibly dousing with water or a diluted solution of bleach or vinegar to dissuade charges.

## Pregnancy

Without ultrasound or other special tools, determining if a sheep is pregnant is difficult. Ewes only begin to visibly show a pregnancy about six weeks before giving birth, so shepherds often rely on the assumption that a ram will impregnate all the ewes in a flock. However, by fitting a ram with a chest harness called a marking harness that holds a special crayon (or raddle, sometimes spelled reddle), ewes that have been mounted are marked with a color. Dye may also be directly applied to the ram's brisket. This measure is not used in flocks where wool is important, since the color of a raddle contaminates it. The crayon in the marking harness can be changed during the breeding cycle to allow for lambing date predictions for each ewe.

After mating, sheep have a gestation period of around five months. Within a few days of the impending birth, ewes begin to behave differently. They may lie down and stand erratically, paw the ground, or otherwise act out of sync with normal flock patterns. An ewe's udder will quickly fill out, and her vulva will swell. Vaginal, uterine or anal prolapse may also occur, in which case either stitching or a physical retainer can be used to hold the orifice in if the problem persists. Usually ewes that experience serious issues while lambing such as prolapse, will be discarded from the flock to avoid further complications in upcoming years.

### Artificial insemination and embryo transfer

In addition to natural insemination by rams, artificial insemination and embryo transfers have been used in sheep breeding programs for many years in Australia and New Zealand. These programs have become more commonplace in the United States during the 2000s as the number of veterinarians qualified to perform these types of procedures with proficiency have grown. However, ovine AI is a relatively complicated procedure compared to other livestock. Unlike cattle or goats, which have straight cervices that can be vaginally inseminated, ewes have a curved cervix which is more difficult to access. Additionally, breeders were until recently unable to control their ewe's estrus cycles. The ability to control the estrus cycle is much easier today because of products that safely assist in aligning heat cycles. Some examples of products are PG600, CIDRs, Estrumate and Folltropin V. These products contain progesterone which will bring on the induction of estrus in ewes (sheep) during seasonal anestrus. Seasonal anestrus is when ewes do not have regular estrous cycles outside the natural breeding season.

Historically, vaginal insemination of sheep only produced 40-60% success rates, and was thus called a "shot in the dark" (SID). In the 1980s, Australian researchers developed a laparoscopic insemination procedure which, combined with the use of progestogen and pregnant mare's serum gonadotropin (PMSG), yielded much higher success rates (50-80% or more), and has become the standard for artificial insemination of sheep in the 21st century.

Semen collection is naturally an integral component of this entire process. Once semen has been collected it can be used immediately for insemination or slowly frozen for use at a later date. Fresh semen is recognized as the method of choice as it lives longer and yields higher conception rates. Frozen semen will work but it must be the highest quality of semen and the ewes must be inseminated twice in the same day. The marketing of ram semen is a major part of this industry. Producers owning prize winning rams have found this to be a good avenue to leverage the accolades of their most famous animals.

During embryo transfer (ET) a minor surgical procedure with almost no risk of injury or infection when performed properly, sheep laparoscopy allows the importation of improved genetics, even of breeds which may otherwise be non-existent in certain countries due to the regulation of live animal imports. Embryo transfer procedures are used to allow producers to maximize those females that produce the best lambs/kids either for retention into the flock or for sale to other producers. ET also allows producers to continue to utilize a ewe/doe that may not physically be able to carry or feed a set of lambs. ET can allow a producer to grow his flock quickly with above average individuals of similar bloodlines. The primary industry to utilize this technology in the United States is the club lamb breeders and exhibitors. It is a common practice in the commercial sheep industries of Australia, New Zealand, and South America.

Average success rates in Embryo Transfer in terms of embryos recovered can vary widely. Each breed will respond differently to the ET process. Typically white faced ewes and does are more fertile than black faced ewes. A range of zero to the mid 20s in terms of viable embryos recovered from a flush procedure can be expected. Over the course of a year the average is 6.8 transferable eggs per donor with a 75% conception rate for those eggs.

### Infertility

Infertility can be attributed to many aspects in managerial practices as well as health factors. One of the main reasons low lambing percentages can be seen in a flock is due to mineral and vitamin deficiencies. The main vitamins and minerals that play a major role in fertility are selenium, copper, vitamin A and D. Other factors that affect fertility and potentially cause abortion are infectious diseases, inappropriate body condition or toxins in feed.

## Lambing

As the time for lambing approaches, the lamb will drop causing the ewe to have a swayback, exhibit restless behaviour and show a sunken appearance in front of the hipbone area. When birth is imminent, contractions begin to take place, and the fitful behavior of the ewe may increase. A normal labor may take one to several hours, depending on how many lambs are present, the age of the ewe, and her physical and nutritional condition prior to the birth. Though some breeds may regularly produce larger litters of lambs (records stand around nine lambs at once), most produce either single or twin lambs. The number of lambs a ewe produces per year is known as the lambing percentage. The condition of the ewe during breeding season will impact the lambing percentage as well as the size of the lambs. At some point, usually at the beginning of labor or soon after the births have occurred, ewes and lambs may be confined to small lambing jugs. These pens, which are generally two to eight feet (0.6 to 2.4 m) in length and width, are designed to aid both careful observation of ewes and to cement the bond between them and their lambs.

Ovine obstetrics can be problematic. By selectively breeding ewes that produce multiple offspring with higher birth weights for generations, sheep producers have inadvertently caused some domestic sheep to have difficulty lambing. However, it is a myth that sheep cannot lamb without human assistance; many ewes give birth directly in pasture without aid. Balancing ease of lambing with high productivity is one of the dilemmas of sheep breeding. While the majority of births are relatively normal and do not require intervention, many complications may arise. A lamb may present in the normal fashion (with both legs and head forward), but may simply be too large to slide out of the birth canal. This often happens when large rams are crossed with diminutive ewes (this is related to breed, rams are naturally larger than ewes by comparison). Lambs may also present themselves with one shoulder to the side, completely backward, or with only some of their limbs protruding. Lambs may also be spontaneously aborted or stillborn. Reproductive failure is a common consequence of infections such as toxoplasmosis and foot-and-mouth disease. Some types of abortion in sheep are preventable by vaccinations against these infections.

In the case of any such problems, those present at lambing (who may or may not include a veterinarian, most shepherds become accomplished at lambing to some degree) may assist the ewe in extracting or repositioning lambs. In severe cases, a cesarean section will be required to remove the lamb. After the birth, ewes ideally break the amniotic sac (if it is not broken during labor), and begin licking clean the lamb. The licking clears the nose and mouth, dries the lamb, and stimulates it. Lambs that are breathing and healthy at this point begin trying to stand, and ideally do so between a half and full hour, with help from the mother. Generally after lambs stand, the umbilical cord is trimmed to about an inch (2.5 centimeters). Once trimmed, a small container (such as a film canister) of iodine is held against the lamb's belly over the remainder of the cord to prevent infection.

## Postnatal care

In normal situations, lambs nurse after standing, receiving vital colostrum milk. Lambs that either fail to nurse or are prevented from doing so by the ewe require aid in order to live. If coaxing the pair to accept nursing does not work, one of several steps may then be taken. Ewes may be held or tied to force them to accept a nursing lamb. If a lamb is not eating, a stomach tube may also be used to force feed the lamb in order to save its life. In the case of a permanently rejected lamb, a shepherd may then attempt to foster an orphaned lamb onto another ewe. Lambs are also sometimes fostered after the death of their mother, either from the birth or other event.

Scent plays a large factor in ewes recognizing their lambs, so disrupting the scent of a newborn lamb with washing or over-handling may cause a ewe to reject it. Conversely, various methods of imparting the scent of a ewe's own lamb to an orphaned one may be useful in fostering. If an orphaned lamb cannot be fostered, then it usually becomes what is known as a bottle lamb—a lamb raised by people and fed via bottle.

After lambs are stabilized, lamb marking is carried out – this includes ear tagging, docking, castration and usually vaccination. Ear tags with numbers are the primary mode of identification when sheep are not named; it is also the legal manner of animal identification in the European Union: the number may identify the individual sheep or only its flock. When performed at an early age, ear tagging seems to cause little or no discomfort to lambs. However, using tags improperly or using tags not designed for sheep may cause discomfort, largely due to excess weight of tags for other animals.

Ram lambs not intended for breeding are castrated, though some shepherds choose to avoid the procedure for ethical, economic or practical reasons. Ram lambs that will be slaughtered or separated from ewes before sexual maturity are not usually castrated. In most breeds, lambs' tails are docked for health reasons. The tail may be removed just below the lamb's caudal tail flaps (docking shorter than this may cause health problems such as rectal prolapse), but in some breeds the tail is left longer, or is not docked at all. Docking is not necessary in short-tailed breeds, and it is not usually done in breeds in which a long tail is valued, such as Zwartbles. Though docking is often considered cruel and unnatural by animal rights activists, it is considered by sheep producers large and small alike to be a critical step in maintaining the health of sheep. Long, wooly tails make shearing more difficult, interfere with mating, and make sheep extremely susceptible to parasites, especially those that cause flystrike. Both castration and docking can be performed with several instruments. An elastrator places a tight band of rubber around an area, causing it to atrophy and fall off in a number of weeks. This process is bloodless and does not seem to cause extended suffering to lambs, who tend to ignore it after several hours. In addition to the elastrator, a Burdizzo, emasculator, heated chisel or knife are sometimes used. After one to three days in the lambing jugs, ewes and lambs are usually sufficiently stabilized to allow reintroduction to the rest of the flock.

## Commercial sheep breeding

In the large sheep producing nations of South America, Australia and New Zealand sheep are usually bred on large tracts of land with much less intervention from the graziers or breeders. Merinos, and much of the land in these countries does not lend itself to the mob intervention that is found in smaller flock breeding countries. In these countries there is little need, and no option but for ewes to lamb outdoors as there are insufficient structures to handle the large flocks of ewes there. New Zealand ewes produce 36 million lambs each spring time, which is an average of 2,250 lambs per farm. Australian graziers, too, do not receive the financial support that governments in other countries provide to sheep breeders. Low-cost sheep breeding is based on large numbers of sheep per labour unit and having ewes that are capable of unsupervised lambing to produce hardy, active lambs.

## Managerial aspects

For breeders intent on strict improvements to their flocks, ewes are classed and inferior sheep are removed prior to mating in order to maintain or improve the quality of the flock. Muffled (wooly) faces have long been associated with lower fertility rates. Stud or specially selected rams are chosen with aid of objective measurements, genetic information and evaluation services that are now available in Australia and New Zealand. The choice of mating time is governed by many factors including climate, market requirements and feed availability. Rams are typically mated at about 2.5% depending on the age of the sheep, plus consideration as to the size and type of mating paddocks. The mating period ranges from about 6 to 8 weeks in commercial flocks. Longer mating times result in management problems with lamb marking and shearing etc.

Good nutrition is vital to ewes during the last 6 weeks of pregnancy in order to prevent pregnancy toxaemia, especially in twin bearing ewes. Overfeeding, however, may result in over large single lambs and dystocia. Shearing ewes before lambing reduces the number of ewes that are cast (i.e. unable to rise unassisted), and the number of lambs and ewes that are lost. Lambs, too, are aided in finding the udder and suckling a shorn ewe. In addition, shearing the ewe before lambing can increase the quality of the fleece as wool breaking can occur since giving birth is such a major stress on the ewe's body. It is important to keep in mind weather conditions prior to shearing ewes, especially in colder climates.

After shearing ewes are typically placed in well sheltered paddocks that have good feed and water. Attention to ewes that are lambing varies according to the breed, size and locations of properties. Unless they are stud ewes it unlikely that they will receive intensive care. On stations with large paddocks there is a policy of non-interference. On other properties the mobs are inspected by stockmen at varying intervals to stand cast ewes and deal with dystocia. Producers also sometimes quietly drift pregnant ewes away from ewes that have already lambed, in order to prevent mis-mothering.

Lambs are usually marked at three to six weeks of age, but a protracted lambing season may necessitate two markings.

### Inbreeding depression

Inbreeding tends to occur in flocks of limited size and where only a single or a few rams are used. Associated with inbreeding is a decline in progeny performance usually referred to as inbreeding depression. Inbreeding depression has been found for lamb birthweight, average daily weight gain from birth until two months, and litter size. Inbreeding depression can be the cause of diseases and deformities to arise in a flock.

## Other countries

In the major sheep countries of Argentina, Uruguay, Brazil, Peru and Chile, breeders are also utilizing fleece testing and performance recording schemes as a means of improving their flocks.

## New research

In 2008, for the first time in history, researchers at Chiswick CSIRO research station, between Uralla and Armidale, New South Wales have used stem cells to develop surrogate rams and bulls. These males then produce the viable semen of another male.

The approach in these sheep experiments involves irradiating a ram's testes while placing stem cells from a second ram into the testes of the first, ram A. In the following weeks ram A produces semen the usual way, but is using the stem cells of ram B and therefore producing semen carrying the genetics of ram B rather than those of his own. Ram A therefore has effectively become a surrogate ram.

The viable semen is then implanted in the ewe and the many lambs born through this process are proving to be normal and healthy. DNA tests have proved that up to 10% of the lambs are sired by the surrogate ram and carry the genetics of the donor ram.

Another area of research that is growing in importance is the reduction of greenhouse gas emissions, mainly methane, from livestock. Ruminants are responsible for contributing the highest emissions out of all types of animals. Many researchers are conducting studies to determine how manipulating sheep diets may help reduce these dangerous emissions.

Reproduction of sheep