Earth's magnetic field

Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo.

The magnitude of Earth's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 G). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11° with respect to Earth's rotational axis, as if there were an enormous bar magnet placed at that angle through the center of Earth. The North geomagnetic pole actually represents the South pole of Earth's magnetic field, and conversely the South geomagnetic pole corresponds to the north pole of Earth's magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward Earth's South magnetic field, i.e., the North geomagnetic pole near the Geographic North Pole). As of 2015, the North geomagnetic pole was located on Ellesmere Island, Nunavut, Canada.

While the North and South magnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, Earth's field reverses and the North and South Magnetic Poles respectively, abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics.

The magnetosphere is the region above the ionosphere that is defined by the extent of Earth's magnetic field in space. It extends several tens of thousands of kilometres into space, protecting Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects Earth from harmful ultraviolet radiation.

## Significance

Earth's magnetic field deflects most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of the magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.

The study of the past magnetic field of the Earth is known as paleomagnetism. The polarity of the Earth's magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetism to track the past motion of continents. Reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores.

Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass can remain useful for navigation. Using magnetoreception, various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation .

## Characteristics

At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North is the declination (D) or variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination (I) or magnetic dip. The intensity (F) of the field is proportional to the force it exerts on a magnet. Another common representation is in X (North), Y (East) and Z (Down) coordinates.

### Intensity

The intensity of the field is often measured in gauss (G), but is generally reported in microteslas (μT), with 1 G = 100 μT. A nanotesla is also referred to as a gamma (γ). The Earth's field ranges between approximately 25 and 65 μT (0.25 and 0.65 G). By comparison, a strong refrigerator magnet has a field of about 10,000 μT (100 G).

A map of intensity contours is called an isodynamic chart. As the World Magnetic Model shows, the intensity tends to decrease from the poles to the equator. A minimum intensity occurs in the South Atlantic Anomaly over South America while there are maxima over northern Canada, Siberia, and the coast of Antarctica south of Australia.

The intensity of the magnetic field is subject to change over time. A 2021 paleomagnetic study from the University of Liverpool contributed to a growing body of evidence that the Earth's magnetic field cycles with intensity every 200 million years. The lead author stated that "Our findings, when considered alongside the existing datasets, support the existence of an approximately 200-million-year-long cycle in the strength of the Earth's magnetic field related to deep Earth processes."

### Inclination

The inclination is given by an angle that can assume values between -90° (up) to 90° (down). In the northern hemisphere, the field points downwards. It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator. It continues to rotate upwards until it is straight up at the South Magnetic Pole. Inclination can be measured with a dip circle.

An isoclinic chart (map of inclination contours) for the Earth's magnetic field is shown below.

### Declination

Declination is positive for an eastward deviation of the field relative to true north. It can be estimated by comparing the magnetic north–south heading on a compass with the direction of a celestial pole. Maps typically include information on the declination as an angle or a small diagram showing the relationship between magnetic north and true north. Information on declination for a region can be represented by a chart with isogonic lines (contour lines with each line representing a fixed declination).

### Geographical variation

### Dipolar approximation

Near the surface of the Earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the center of the Earth and tilted at an angle of about 11° with respect to the rotational axis of the Earth. The dipole is roughly equivalent to a powerful bar magnet, with its south pole pointing towards the geomagnetic North Pole. This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels the north poles, it must be attracted to the south pole of Earth's magnet. The dipolar field accounts for 80–90% of the field in most locations.

### Magnetic poles

Historically, the north and south poles of a magnet were first defined by the Earth's magnetic field, not vice versa, since one of the first uses for a magnet was as a compass needle. A magnet's North pole is defined as the pole that is attracted by the Earth's North Magnetic Pole when the magnet is suspended so it can turn freely. Since opposite poles attract, the North Magnetic Pole of the Earth is really the south pole of its magnetic field (the place where the field is directed downward into the Earth).

The positions of the magnetic poles can be defined in at least two ways: locally or globally. The local definition is the point where the magnetic field is vertical. This can be determined by measuring the inclination. The inclination of the Earth's field is 90° (downwards) at the North Magnetic Pole and -90° (upwards) at the South Magnetic Pole. The two poles wander independently of each other and are not directly opposite each other on the globe. Movements of up to 40 kilometres (25 mi) per year have been observed for the North Magnetic Pole. Over the last 180 years, the North Magnetic Pole has been migrating northwestward, from Cape Adelaide in the Boothia Peninsula in 1831 to 600 kilometres (370 mi) from Resolute Bay in 2001. The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal).

The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects the Earth's surface are called the North and South geomagnetic poles. If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them. However, the Earth's field has a significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either.

## Magnetosphere

Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the solar wind. This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the interplanetary magnetic field (IMF).

The solar wind exerts a pressure, and if it could reach Earth's atmosphere it would erode it. However, it is kept away by the pressure of the Earth's magnetic field. The magnetopause, the area where the pressures balance, is the boundary of the magnetosphere. Despite its name, the magnetosphere is asymmetric, with the sunward side being about 10 Earth radii out but the other side stretching out in a magnetotail that extends beyond 200 Earth radii. Sunward of the magnetopause is the bow shock, the area where the solar wind slows abruptly.

Inside the magnetosphere is the plasmasphere, a donut-shaped region containing low-energy charged particles, or plasma. This region begins at a height of 60 km, extends up to 3 or 4 Earth radii, and includes the ionosphere. This region rotates with the Earth. There are also two concentric tire-shaped regions, called the Van Allen radiation belts, with high-energy ions (energies from 0.1 to 10 MeV). The inner belt is 1–2 Earth radii out while the outer belt is at 4–7 Earth radii. The plasmasphere and Van Allen belts have partial overlap, with the extent of overlap varying greatly with solar activity.

As well as deflecting the solar wind, the Earth's magnetic field deflects cosmic rays, high-energy charged particles that are mostly from outside the Solar System. Many cosmic rays are kept out of the Solar System by the Sun's magnetosphere, or heliosphere. By contrast, astronauts on the Moon risk exposure to radiation. Anyone who had been on the Moon's surface during a particularly violent solar eruption in 2005 would have received a lethal dose.

Some of the charged particles do get into the magnetosphere. These spiral around field lines, bouncing back and forth between the poles several times per second. In addition, positive ions slowly drift westward and negative ions drift eastward, giving rise to a ring current. This current reduces the magnetic field at the Earth's surface. Particles that penetrate the ionosphere and collide with the atoms there give rise to the lights of the aurorae while also emitting X-rays.

The varying conditions in the magnetosphere, known as space weather, are largely driven by solar activity. If the solar wind is weak, the magnetosphere expands; while if it is strong, it compresses the magnetosphere and more of it gets in. Periods of particularly intense activity, called geomagnetic storms, can occur when a coronal mass ejection erupts above the Sun and sends a shock wave through the Solar System. Such a wave can take just two days to reach the Earth. Geomagnetic storms can cause a lot of disruption; the "Halloween" storm of 2003 damaged more than a third of NASA's satellites. The largest documented storm, the Carrington Event, occurred in 1859. It induced currents strong enough to disrupt telegraph lines, and aurorae were reported as far south as Hawaii.

## Time dependence

### Short-term variations

The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the ionosphere (ionospheric dynamo region) and magnetosphere, and some changes can be traced to geomagnetic storms or daily variations in currents. Changes over time scales of a year or more mostly reflect changes in the Earth's interior, particularly the iron-rich core.

Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the K-index.

Data from THEMIS show that the magnetic field, which interacts with the solar wind, is reduced when the magnetic orientation is aligned between Sun and Earth – opposite to the previous hypothesis. During forthcoming solar storms, this could result in blackouts and disruptions in artificial satellites.

### Secular variation

Changes in Earth's magnetic field on a time scale of a year or more are referred to as secular variation. Over hundreds of years, magnetic declination is observed to vary over tens of degrees. The animation shows how global declinations have changed over the last few centuries.

The direction and intensity of the dipole change over time. Over the last two centuries the dipole strength has been decreasing at a rate of about 6.3% per century. At this rate of decrease, the field would be negligible in about 1600 years. However, this strength is about average for the last 7 thousand years, and the current rate of change is not unusual.

A prominent feature in the non-dipolar part of the secular variation is a westward drift at a rate of about 0.2° per year. This drift is not the same everywhere and has varied over time. The globally averaged drift has been westward since about 1400 AD but eastward between about 1000 AD and 1400 AD.

Changes that predate magnetic observatories are recorded in archaeological and geological materials. Such changes are referred to as paleomagnetic secular variation or paleosecular variation (PSV). The records typically include long periods of small change with occasional large changes reflecting geomagnetic excursions and reversals.

In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth's magnetic field reached \~10° per year – almost 100 times faster than current changes and 10 times faster than previously thought.

Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could have shifted at a rate of up to 6° per day at some time in Earth's history, which significantly challenges the popular understanding of how the Earth's magnetic field works. This finding was later attributed to unusual rock magnetic properties of the lava flow under study, not rapid field change, by one of the original authors of the 1995 study.

### Magnetic field reversals

Although generally Earth's field is approximately dipolar, with an axis that is nearly aligned with the rotational axis, occasionally the North and South geomagnetic poles trade places. Evidence for these geomagnetic reversals can be found in basalts, sediment cores taken from the ocean floors, and seafloor magnetic anomalies. Reversals occur nearly randomly in time, with intervals between reversals ranging from less than 0.1 million years to as much as 50 million years. The most recent geomagnetic reversal, called the Brunhes–Matuyama reversal, occurred about 780,000 years ago. A related phenomenon, a geomagnetic excursion, takes the dipole axis across the equator and then back to the original polarity. The Laschamp event is an example of an excursion, occurring during the last ice age (41,000 years ago).

The past magnetic field is recorded mostly by strongly magnetic minerals, particularly iron oxides such as magnetite, that can carry a permanent magnetic moment. This remanent magnetization, or remanence, can be acquired in more than one way. In lava flows, the direction of the field is "frozen" in small minerals as they cool, giving rise to a thermoremanent magnetization. In sediments, the orientation of magnetic particles acquires a slight bias towards the magnetic field as they are deposited on an ocean floor or lake bottom. This is called detrital remanent magnetization.

Thermoremanent magnetization is the main source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells up from the mantle, cools to form new basaltic crust on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Earth's field. When the Earth's field reverses, new basalt records the reversed direction. The result is a series of stripes that are symmetric about the ridge. A ship towing a magnetometer on the surface of the ocean can detect these stripes and infer the age of the ocean floor below. This provides information on the rate at which seafloor has spread in the past.

Radiometric dating of lava flows has been used to establish a geomagnetic polarity time scale, part of which is shown in the image. This forms the basis of magnetostratigraphy, a geophysical correlation technique that can be used to date both sedimentary and volcanic sequences as well as the seafloor magnetic anomalies.

### Earliest appearance

Paleomagnetic studies of Paleoarchean lava in Australia and conglomerate in South Africa have concluded that the magnetic field has been present since at least about .

### Future

Starting in the late 1800s and throughout the 1900s and later, the overall geomagnetic field has become weaker; the present strong deterioration corresponds to a 10–15% decline and has accelerated since 2000; geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value, from circa year 1 AD. The rate of decrease and the current strength are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks.

The nature of Earth's magnetic field is one of heteroscedastic (seemingly random) fluctuation. An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength. It has gone up and down in the past for unknown reasons. Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases.

The Earth's magnetic north pole is drifting from northern Canada towards Siberia with a presently accelerating rate—10 kilometres (6.2 mi) per year at the beginning of the 1900s, up to 40 kilometres (25 mi) per year in 2003, and since then has only accelerated.

## Physical origin

### Earth's core and the geodynamo

The Earth's magnetic field is believed to be generated by electric currents in the conductive iron alloys of its core, created by convection currents due to heat escaping from the core.

The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids. The Earth's field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core. The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about 6,000 K (5,730 °C; 10,340 °F), to the core-mantle boundary, which is about 3,800 K (3,530 °C; 6,380 °F). The heat is generated by potential energy released by heavier materials sinking toward the core (planetary differentiation, the iron catastrophe) as well as decay of radioactive elements in the interior. The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core.

The mechanism by which the Earth generates a magnetic field is known as a geodynamo. The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force). These effects can be combined in a partial differential equation for the magnetic field called the magnetic induction equation,

$\frac{\partial \mathbf{B}}{\partial t} = \eta \nabla^2 \mathbf{B} + \nabla \times (\mathbf{u} \times \mathbf{B}),$

where u is the velocity of the fluid; B is the magnetic B-field; and η=1/σμ is the magnetic diffusivity, which is inversely proportional to the product of the electrical conductivity σ and the permeability μ . The term ∂B/∂t is the time derivative of the field; ∇<sup>2</sup> is the Laplace operator and ∇× is the curl operator.

The first term on the right hand side of the induction equation is a diffusion term. In a stationary fluid, the magnetic field declines and any concentrations of field spread out. If the Earth's dynamo shut off, the dipole part would disappear in a few tens of thousands of years.

In a perfect conductor ($\sigma = \infty\;$), there would be no diffusion. By Lenz's law, any change in the magnetic field would be immediately opposed by currents, so the flux through a given volume of fluid could not change. As the fluid moved, the magnetic field would go with it. The theorem describing this effect is called the frozen-in-field theorem. Even in a fluid with a finite conductivity, new field is generated by stretching field lines as the fluid moves in ways that deform it. This process could go on generating new field indefinitely, were it not that as the magnetic field increases in strength, it resists fluid motion.

The motion of the fluid is sustained by convection, motion driven by buoyancy. The temperature increases towards the center of the Earth, and the higher temperature of the fluid lower down makes it buoyant. This buoyancy is enhanced by chemical separation: As the core cools, some of the molten iron solidifies and is plated to the inner core. In the process, lighter elements are left behind in the fluid, making it lighter. This is called compositional convection. A Coriolis effect, caused by the overall planetary rotation, tends to organize the flow into rolls aligned along the north–south polar axis.

A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a T-Tauri phase in which the solar wind would have had a magnetic field orders of magnitude larger than the present solar wind. However, much of the field may have been screened out by the Earth's mantle. An alternative source is currents in the core-mantle boundary driven by chemical reactions or variations in thermal or electric conductivity. Such effects may still provide a small bias that are part of the boundary conditions for the geodynamo.

The average magnetic field in the Earth's outer core was calculated to be 25 gauss, 50 times stronger than the field at the surface.

#### Numerical models

Simulating the geodynamo by computer requires numerically solving a set of nonlinear partial differential equations for the magnetohydrodynamics (MHD) of the Earth's interior. Simulation of the MHD equations is performed on a 3D grid of points and the fineness of the grid, which in part determines the realism of the solutions, is limited mainly by computer power. For decades, theorists were confined to creating kinematic dynamo computer models in which the fluid motion is chosen in advance and the effect on the magnetic field calculated. Kinematic dynamo theory was mainly a matter of trying different flow geometries and testing whether such geometries could sustain a dynamo.

The first self-consistent dynamo models, ones that determine both the fluid motions and the magnetic field, were developed by two groups in 1995, one in Japan and one in the United States. The latter received attention because it successfully reproduced some of the characteristics of the Earth's field, including geomagnetic reversals.

### Effect of ocean tides

The oceans contribute to Earth's magnetic field. Seawater is an electrical conductor, and therefore interacts with the magnetic field. As the tides cycle around the ocean basins, the ocean water essentially tries to pull the geomagnetic field lines along. Because the salty water is slightly conductive, the interaction is relatively weak: the strongest component is from the regular lunar tide that happens about twice per day (M2). Other contributions come from ocean swell, eddies, and even tsunamis.

The strength of the interaction depends also on the temperature of the ocean water. The entire heat stored in the ocean can now be inferred from observations of the Earth's magnetic field.

### Currents in the ionosphere and magnetosphere

Electric currents induced in the ionosphere generate magnetic fields (ionospheric dynamo region). Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations that can deflect surface magnetic fields by as much as 1°. Typical daily variations of field strength are about 25 nT (one part in 2000), with variations over a few seconds of typically around 1 nT (one part in 50,000).

## Measurement and analysis

### Detection

The Earth's magnetic field strength was measured by Carl Friedrich Gauss in 1832 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years. The Magsat satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later Ørsted satellite allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of South Africa.

Governments sometimes operate units that specialize in measurement of the Earth's magnetic field. These are geomagnetic observatories, typically part of a national Geological survey, for example, the British Geological Survey's Eskdalemuir Observatory. Such observatories can measure and forecast magnetic conditions such as magnetic storms that sometimes affect communications, electric power, and other human activities.

The International Real-time Magnetic Observatory Network, with over 100 interlinked geomagnetic observatories around the world, has been recording the Earth's magnetic field since 1991.

The military determines local geomagnetic field characteristics, in order to detect anomalies in the natural background that might be caused by a significant metallic object such as a submerged submarine. Typically, these magnetic anomaly detectors are flown in aircraft like the UK's Nimrod or towed as an instrument or an array of instruments from surface ships.

Commercially, geophysical prospecting companies also use magnetic detectors to identify naturally occurring anomalies from ore bodies, such as the Kursk Magnetic Anomaly.

### Crustal magnetic anomalies

Magnetometers detect minute deviations in the Earth's magnetic field caused by iron artifacts, kilns, some types of stone structures, and even ditches and middens in archaeological geophysics. Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped. Basalt — the iron-rich, volcanic rock making up the ocean floor — contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.

### Statistical models

Each measurement of the magnetic field is at a particular place and time. If an accurate estimate of the field at some other place and time is needed, the measurements must be converted to a model and the model used to make predictions.

#### Spherical harmonics

The most common way of analyzing the global variations in the Earth's magnetic field is to fit the measurements to a set of spherical harmonics. This was first done by Carl Friedrich Gauss. Spherical harmonics are functions that oscillate over the surface of a sphere. They are the product of two functions, one that depends on latitude and one on longitude. The function of longitude is zero along zero or more great circles passing through the North and South Poles; the number of such nodal lines is the absolute value of the order m. The function of latitude is zero along zero or more latitude circles; this plus the order is equal to the degree l. Each harmonic is equivalent to a particular arrangement of magnetic charges at the center of the Earth. A monopole is an isolated magnetic charge, which has never been observed. A dipole is equivalent to two opposing charges brought close together and a quadrupole to two dipoles brought together. A quadrupole field is shown in the lower figure on the right.

Spherical harmonics can represent any scalar field (function of position) that satisfies certain properties. A magnetic field is a vector field, but if it is expressed in Cartesian components X, Y, Z, each component is the derivative of the same scalar function called the magnetic potential. Analyses of the Earth's magnetic field use a modified version of the usual spherical harmonics that differ by a multiplicative factor. A least-squares fit to the magnetic field measurements gives the Earth's field as the sum of spherical harmonics, each multiplied by the best-fitting Gauss coefficient g<sub>m</sub><sup>l</sup> or h<sub>m</sub><sup>l</sup>.

The lowest-degree Gauss coefficient, g<sub>0</sub><sup>0</sup>, gives the contribution of an isolated magnetic charge, so it is zero. The next three coefficients – g<sub>1</sub><sup>0</sup>, g<sub>1</sub><sup>1</sup>, and h<sub>1</sub><sup>1</sup> – determine the direction and magnitude of the dipole contribution. The best fitting dipole is tilted at an angle of about 10° with respect to the rotational axis, as described earlier.

#### Radial dependence

Spherical harmonic analysis can be used to distinguish internal from external sources if measurements are available at more than one height (for example, ground observatories and satellites). In that case, each term with coefficient g<sub>m</sub><sup>l</sup> or h<sub>m</sub><sup>l</sup> can be split into two terms: one that decreases with radius as 1/r<sup>l+1</sup> and one that increases with radius as r<sup>l</sup>. The increasing terms fit the external sources (currents in the ionosphere and magnetosphere). However, averaged over a few years the external contributions average to zero.

The remaining terms predict that the potential of a dipole source (l=1) drops off as 1/r<sup>2</sup>. The magnetic field, being a derivative of the potential, drops off as 1/r<sup>3</sup>. Quadrupole terms drop off as 1/r<sup>4</sup>, and higher order terms drop off increasingly rapidly with the radius. The radius of the outer core is about half of the radius of the Earth. If the field at the core-mantle boundary is fit to spherical harmonics, the dipole part is smaller by a factor of about 8 at the surface, the quadrupole part by a factor of 16, and so on. Thus, only the components with large wavelengths can be noticeable at the surface. From a variety of arguments, it is usually assumed that only terms up to degree 14 or less have their origin in the core. These have wavelengths of about 2,000 km (1,200 mi) or less. Smaller features are attributed to crustal anomalies.

#### Global models

The International Association of Geomagnetism and Aeronomy maintains a standard global field model called the International Geomagnetic Reference Field (IGRF). It is updated every five years. The 11th-generation model, IGRF11, was developed using data from satellites (Ørsted, CHAMP and SAC-C) and a world network of geomagnetic observatories. The spherical harmonic expansion was truncated at degree 10, with 120 coefficients, until 2000. Subsequent models are truncated at degree 13 (195 coefficients).

Another global field model, called the World Magnetic Model, is produced jointly by the United States National Centers for Environmental Information (formerly the National Geophysical Data Center) and the British Geological Survey. This model truncates at degree 12 (168 coefficients) with an approximate spatial resolution of 3,000 kilometers. It is the model used by the United States Department of Defense, the Ministry of Defence (United Kingdom), the United States Federal Aviation Administration (FAA), the North Atlantic Treaty Organization (NATO), and the International Hydrographic Organization as well as in many civilian navigation systems.

The above models only take into account the "main field" at the core-mantle boundary. Although generally good enough for navigation, higher-accuracy use cases require smaller-scale magnetic anomalies and other variations to be considered. Some examples are (see geomag.us ref for more):

- The "comprehensive modeling" (CM) approach by the Goddard Space Flight Center (NASA and GSFC) and the Danish Space Research Institute. CM attempts to reconcile data with greatly varying temporal and spatial resolution from ground and satellite sources. The latest version as of 2022 is CM5 of 2016. It provides separate components for main field plus lithosphere (crustal), M2 tidal, and primary/induced magnetosphere/ionosphere variations.
- The US National Centers for Environmental Information developed the Enhanced Magnetic Model (EMM), which extends to degree and order 790 and resolves magnetic anomalies down to a wavelength of 56 kilometers. It was compiled from satellite, marine, aeromagnetic and ground magnetic surveys. As of 2018, the latest version, EMM2017, includes data from The European Space Agency's Swarm satellite mission.

For historical data about the main field, the IGRF may be used back to year 1900. A specialized GUFM1 model estimates back to year 1590 using ship's logs. Paleomagnetic research has produced models dating back to 10,000 BCE.

## Biomagnetism

Animals, including birds and turtles, can detect the Earth's magnetic field, and use the field to navigate during migration. Some researchers have found that cows and wild deer tend to align their bodies north–south while relaxing, but not when the animals are under high-voltage power lines, suggesting that magnetism is responsible. Other researchers reported in 2011 that they could not replicate those findings using different Google Earth images.

Very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds, which use the Earth's magnetic field to navigate. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds; instead, the culprits have frequencies between 2 kHz and 5 MHz. These include AM radio signals and ordinary electronic equipment that might be found in businesses or private homes.

## See also

- Geomagnetic jerk
- Geomagnetic latitude
- Magnetic field of Mars
- Magnetotellurics
- Operation Argus
- South Atlantic Anomaly

Magnetic field that extends from the Earth's outer and inner core to where it meets the solar wind


HMS Vanguard (23)

HMS Vanguard was a British fast battleship built during the Second World War and commissioned after the war ended. She was the largest and fastest of the Royal Navy's battleships, the only ship of her class, and the last battleship to be built.

The Royal Navy anticipated being outnumbered by the combined German and Japanese battleships in the early 1940s, and had therefore started building the Lion-class battleships. However, the time-consuming construction of the triple-16-inch (406 mm) turrets for the Lion class would delay their completion until 1943 at the earliest. The British had enough 15-inch (381 mm) guns and turrets in storage to allow one ship of a modified Lion-class design with four twin-15-inch turrets to be completed faster than the Lion-class vessels that had already been laid down. Work on Vanguard was started and stopped several times during the war, and her design was revised several times during her construction to reflect war experience. These stoppages and changes prevented her from being completed before the end of the war.

Vanguard's first task after completing her sea trial at the end of 1946 was, early the next year, to convey King George VI and his family on the first Royal Tour of South Africa by a reigning monarch. While refitting after her return, she was selected for another Royal Tour of Australia and New Zealand in 1948. This was cancelled due to King George's declining health and Vanguard briefly became flagship of the Mediterranean Fleet in early 1949. After her return home in mid-1949, she became flagship of the Home Fleet Training Squadron. Throughout her career, the battleship usually served as the flagship of any unit to which she was assigned. During the early 1950s, Vanguard was involved in a number of training exercises with NATO forces. In 1953 she participated in Queen Elizabeth II's Coronation Review. While she was refitting in 1955, the Admiralty announced that the ship was going to be put into reserve upon completion of the work. Vanguard was sold for scrap and was broken up beginning in 1960.

## Design and description

By early 1939 it was clear that the first two Lion-class battleships could not be delivered before 1943 at the earliest and that further battleship construction would be necessary to match the German and Japanese battleships already under construction. The main constraint on the construction of any new battleships was the limited available capacity and the time required to build large-calibre guns and their gun turrets. Using four existing twin 15-inch mountings offered the possibility of bypassing this bottleneck and allowed the construction of a single fast battleship more quickly than building more Lion-class ships. The turrets were originally built for the battlecruisers Courageous and Glorious during the First World War, and were removed during the conversions of these ships to aircraft carriers in the 1920s. To save time, the Lion design was modified to accommodate the four turrets, and preliminary design work began in July 1939. The square or transom stern was retained as it was estimated to improve speed at full power by 0.33 knots (0.61 km/h; 0.38 mph). This made Vanguard the only British battleship built with a transom stern, as the Lions were never finished.

Design work was suspended on 11 September 1939, after the start of the Second World War, but resumed in February 1940 after the First Lord of the Admiralty, Winston Churchill, expressed an interest in the ship. The design was modified to increase protection against shell splinters on the unprotected sides of the ship's hull, the armour of the secondary armament was increased to resist 500-pound (230 kg) semi-armour-piercing bombs, and the splinter belt's thickness fore and aft of the main armour belt was reduced by 0.5 inches (12.7 mm) in compensation. A small conning tower was added aft, and four Unrotated Projectile mounts were added to supplement the six octuple-barrel 2-pounder anti-aircraft mounts already planned.

More pressing commitments forced the preliminary design work to be suspended again in June; when it resumed in October the design was modified again in light of recent war experience. Greater fuel capacity was added and the armour protection improved, but these changes deepened the design's draught to beyond the 34-foot (10.4 m) limit of the Suez Canal. The thickness of the main belt was reduced by 1 inch (25 mm) to save weight, but the primary method chosen to reduce the draught was to increase the beam by 2.5 feet (0.76 m). This exceeded the width of the docks at Rosyth and Plymouth, which severely limited the number of docks that could handle the ship, but the changes were approved by the Board of Admiralty on 17 April 1941. The ship had already been ordered on 14 March under the 1940 Emergency War Programme, although the drawings were not turned over to John Brown & Company until ten days later.

Vanguard's design was revised again, while the ship was under construction in 1942, to reflect lessons learned from the loss of the King George V-class battleship Prince of Wales and operations with the other battleships. The longitudinal distance between the inboard and outboard propellers was increased from 33.5 to 51.5 feet (10.2 to 15.7 m) to reduce the chance of a single torpedo wrecking both propeller shafts on one side and watertight access trunks were added to all spaces below the deep waterline to prevent the progressive flooding through open watertight doors and hatches that had happened to Prince of Wales. This change and the relocation of some of the 5.25-inch (133 mm) ammunition handling rooms from the lower deck to the middle deck seriously delayed the ship's completion. The design requirement that the guns of 'A' turret be capable of firing straight ahead at 0° of elevation was sacrificed to allow her freeboard forward to be increased, and her bow was reshaped to make it less prone to shipping water and throwing sea spray in head seas. The ship's fuel supply was increased from 4,400 long tons (4,500 t) to 4,850 long tons (4,930 t) to prevent the fuel shortage problems suffered by King George V and Rodney during their pursuit of the German battleship Bismarck. The Unrotated Projectile mounts were deleted from the design and the light anti-aircraft armament was increased to a total of 76 two-pounders in one quadruple, and nine octuple mounts and 24 Oerlikon 20 mm cannon were also added in 12 twin mounts. Space for these was made available by removing the two floatplanes, the catapult and their associated facilities.

A proposal was made in 1942 to convert Vanguard to an aircraft carrier. The Director of Naval Construction stated that doing so along the lines of the Audacious class would present no major difficulties but would require six months to redesign the ship. The proposal was formally rejected on 17 July.

### General characteristics

Vanguard had an overall length of 814 feet 4 inches (248.2 m), a beam of 107 feet 6 inches (32.8 m) and a draught of 36 feet (11 m) at deep load. She displaced 44,500 long tons (45,200 t) at standard load and 51,420 long tons (52,250 t) at deep load. The ship was significantly larger than her predecessors of the class, almost 50 feet (15.2 m) longer and displaced about 6,000 long tons (6,100 t) more than the older ships at deep load. Vanguard was overweight by some 2,200 long tons (2,200 t), which magnified the difference. The ship had a complete double bottom 5 feet (1.5 m) deep and she was divided into 27 main compartments by watertight bulkheads.

The King George V-class ships had been built with almost no sheer to the main deck forwards to allow 'A' turret to fire straight forward at zero elevation, resulting in those ships being wet forward. Vanguard was redesigned as a result of this experience, significant sheer and flare being added to the bow. The ship's seaworthiness was well regarded, and the ship was able to keep an even keel in rough seas. At full load Vanguard had a metacentric height of 8.2 feet (2.5 m).

As a fleet flagship, her complement was 115 officers and 1,860 men in 1947. Air conditioning was provided for many of the ship's control spaces, and asbestos insulation was provided on exposed areas of the ship's sides, decks and bulkheads. Steam heating was provided for her armament, instruments, look-out positions and other equipment to make Vanguard suitable for operations in the Arctic. An Action Information Centre was fitted below the main armour deck with facilities to track aircraft and ships around Vanguard.

### Propulsion

To save design time, the four-shaft unit machinery from the Lion-class battleship was duplicated with alternating boiler and engine rooms. Vanguard had four sets of single-reduction geared Parsons steam turbines housed in separate engine rooms. Each set consisted of one high-pressure and one low-pressure turbine, driving a propeller 14 feet 9 inches (4.5 m) in diameter. The turbines were powered by eight Admiralty 3-drum boilers in four boiler rooms at a working pressure of 350 psi (2,413 kPa; 25 kgf/cm2) and temperature of 700 °F (371 °C). The engines were designed to produce a total of 130,000 shaft horsepower (97,000 kW) and a speed of 30 knots (56 km/h; 35 mph), but achieved more than 136,000 shp (101,000 kW) during the ship's sea trials in July 1946, when she reached a speed of 31.57 knots (58.47 km/h; 36.33 mph). After trials, the three-bladed propellers on the inboard shafts were replaced by five-bladed propellers to reduce vibrations of the inboard propeller shafts, but this was a failure.

Vanguard was designed to carry 4,850 long tons of fuel oil and 427 long tons (434 t) of diesel fuel. With a clean bottom she could steam at a speed of 15 knots (28 km/h; 17 mph) for 8,250 nautical miles (15,280 km; 9,490 mi). The ship had four 480-kilowatt (640 hp) turbogenerators and four 450-kilowatt (600 hp) diesel generators that supplied electricity via the common ring main at 220 volts. Their total output of 3,720 kilowatts (4,990 hp) was the largest of any British battleship.

### Armament

The ship's main armament consisted of eight 42-calibre BL 15-inch Mk I guns in four twin hydraulically powered gun turrets, 'A', 'B', 'X' and 'Y' from bow to stern. The guns were loaded at +5°; when the turrets were modernised to the Mk I(N) RP12 design, their maximum elevation was increased from 20° to +30°. They fired 1,938-pound (879 kg) projectiles at a muzzle velocity of 2,458 ft/s (749 m/s), for a maximum normal range of 33,550 yards (30,680 m). The guns could use supercharges, which gave a maximum range of 37,870 yards (34,630 m) with the same shells. Their rate of fire was two rounds per minute. Vanguard carried 100 shells per gun.

The old 15-inch turrets had been designed when the customary practice was to place the magazine above the shell room, and it was not cost-effective to modify the ammunition hoists to accommodate the opposite arrangement, which had been adopted after the Battle of Jutland demonstrated the dangers of exposing the magazines to long-range gunfire. The ship was provided with a powder-handling room above the shell room to mimic the arrangement that the turrets' hoists were designed to handle, and another set of hoists moved the propellant charges from the magazines to the powder-handling room. The charges were stowed in cases to reduce their exposure to fire.

The secondary armament consisted of sixteen 50-calibre QF 5.25-inch Mk I\* dual-purpose guns in eight twin gun mounts. They had a maximum depression of −5° and a maximum elevation of 70°. They fired an 80-pound (36.3 kg) high-explosive shell at a muzzle velocity of 2,672 ft/s (814 m/s). The improved RP10 spec 5.25 turrets on Vanguard were claimed to be fully automatic, with a power-rammed breech and automatic tracking and elevation under radar control enabling a rate of fire of about 18 rounds per minute. At maximum elevation, the guns had a maximum range of 24,070 yards (22,010 m). 391 rounds were provided for each gun.

Short-range air defence was provided by 73 Bofors 40 mm AA guns in a variety of mountings. Vanguard had ten sextuple-barrel power-operated mounts concentrated in the superstructure and stern, a twin-barrel mount on 'B' turret and 11 power-operated single mounts on the upper deck and rear superstructure. All mounts could depress to −10° and elevate to +90°. The 40-millimetre (1.6 in) gun fired a 1.97-pound (0.89 kg) shell at a muzzle velocity of 2,890 ft/s (880 m/s) to a distance of 10,750 yards (9,830 m). The guns' rate of fire was approximately 120 rounds per minute. Space was not available to stow the standard allowance of 1,564 rounds per gun, and Vanguard carried only 1,269 rounds per gun. Two of the single guns on the quarterdeck were removed in 1949, and five others during a major refit in 1954. All of her multiple Bofors mounts were removed at this same time.

### Fire control

Vanguard was unique among British battleships in having remote power control (RPC) for her main, secondary and tertiary guns along with the Admiralty Fire Control Table Mk X for surface fire control of the main armament. There were two director control towers (DCT) for the 15-inch guns, each carrying a "double cheese" Type 274 fire-control radar for range finding and spotting the fall of shot. Each DCT could control all four turrets, 'B' turret could control 'A' and 'X' turrets, and 'X' turret could control 'Y' turret. There were four American Mark 37 DCTs for the 5.25-inch guns, each carrying the twin domes of Type 275 gunnery radar. Each Mark VI sextuple 40 mm Bofors mounting was provided with a separate CRBF ("close range blind fire") director fitted with a Type 262 radar, although the ship never mounted her complete outfit of those directors. The STAAG Mk II 40 mm Bofors mounting carried its own Type 262 on the mounting itself. Other radar sets carried were Type 960 air and surface search, Type 293 target indication and Type 277 radar height finding.

When the 15-inch gun turrets were modernised, their 15-foot (4.6 m) rangefinders were replaced by 30-foot (9.1 m) ones in all turrets except 'A', and they were fitted for RPC in azimuth only. The turrets were also provided with de-humidifying equipment and insulation to improve their habitability.

### Protection

The ship's armour scheme was based on that of the King George V class with a thinner waterline belt and additional splinter protection. Originally the belt armour was equal to that of the older ships, but it had to be reduced to offset weight increases when the design was modified to reflect wartime experience. The waterline 460-foot (140.2 m) main belt was composed of Krupp cemented armour (KCA) 13 inches (330 mm) thick but increased to 14 inches (356 mm) abreast the magazines. It was 24 feet (7.3 m) high and tapered to a thickness of 4.5 inches (114 mm) at the bottom edge of the belt. Fore and aft of the 12-inch (305 mm) transverse bulkheads that closed off the central citadel, the belt continued almost to the ends of the ship. Forward it tapered to a thickness of 2 inches (51 mm) and a height of 8 feet (2.4 m), and aft to the same thickness but a height of 11 feet (3.4 m). At the aft end of the steering gear compartment was a 4-inch (102 mm) transverse bulkhead. After the Battle of the Denmark Strait in 1941, 1.5-inch (38 mm) non-cemented armour bulkheads were added on the sides of the magazines, to protect them from splinters from any hits from plunging shells that might have penetrated the ship's side beneath her belt.

When the gun turrets from the First World War-era battlecruisers were modernised, their KCA faceplates were replaced by new ones 13 inches thick, and their roofs were replaced by 6-inch (152 mm) non-cemented armour plates. Their sides remained 7–9 inches (180–230 mm) in thickness. The barbettes for the 15-inch guns were 13 inches thick on the sides but tapered to 11–12 inches (279–305 mm) closer to the centreline of the ship. The side and roof armour of the 5.25-inch turrets was 2.5 inches (64 mm) thick. Their ammunition hoists were protected by armour 2–6 inches (51–152 mm) thick.

Intended to resist the impact of a 1,000-pound (450 kg) armour-piercing bomb dropped from a height of 14,000 feet (4,300 m), Vanguard's deck protection was identical to that of the King George V class, six-inch non-cemented armour over the magazines that reduced to 5 inches (127 mm) over the machinery spaces. The armour continued forward and aft of the citadel at the lower-deck level. Forward it tapered in steps from five inches down to 2.5 inches near the bow. Aft, it protected the steering gear and propeller shafts with 4.5 inches of armour before tapering to a thickness of 2.5 inches near the stern. Unlike the Germans, French and Americans, the British no longer believed that heavy armour for the conning tower served any real purpose given that the chance of hitting it was very small; Vanguard's conning tower was therefore protected with 3 inches (76 mm) of armour on the face and 2.5 inches on the sides and rear. The secondary conning tower aft had 2 inches (51 mm) of armour on its sides.

Vanguard's underwater protection was enhanced when she was redesigned in 1942 to reflect the lessons learned when Prince of Wales was sunk by Japanese torpedo bombers. It still consisted of a three-layer system of voids and liquid-filled compartments meant to absorb the energy of an underwater explosion. It was bounded on the inside by the 1.75–1.5-inch (44–38 mm) torpedo bulkhead. Her enlarged oil tanks reduced the empty spaces that could flood and cause the ship to list, and greater provision was made to pump these spaces out. The longitudinal bulkheads of the side protection system were raised one deck higher to further subdivide the spaces behind the waterline armour belt. The side protection system had a maximum depth of 15 feet (4.6 m), but this decreased significantly as the ship narrowed at its ends. Over the length of the citadel, this system was found during full-scale trials to be proof against 1,000 pounds (450 kg) of TNT.

## Construction and career

Vanguard was laid down on 2 October 1941 by John Brown and Company of Clydebank, Scotland, with the yard number of 567. After the Japanese invasion of Malaya in December, the ship was given an A1 priority in the hope of finishing her by the end of 1944, and construction of the light cruiser HMS Bellerophon, as well as some merchant shipping, was halted to expedite the ship's completion. This was unsuccessful, however, due to a shortage of skilled labour. As a result, it was not until 30 November 1944 that the ship was launched. Princess Elizabeth presided over this ceremony, the first ship she ever launched, and was presented with a diamond rose brooch to commemorate the event. Two yard workers were killed and six others injured when a "blinding explosion ripped" the ship in a fitting-out basin at Clydebank on 16 September 1945. Captain William Gladstone Agnew assumed command on 15 October 1945. The end of hostilities following Japan's surrender reduced the need for new warships, and consequently the ship was not commissioned until 12 May 1946. By this time, a total of £11,530,503, including £3,186,868 for the modernisation of the main armament, had been spent on producing Vanguard.

After commissioning, the ship spent several months conducting sea trials and training until August, when she began the necessary modifications to serve as a royal yacht for the forthcoming royal tour of South Africa. The Admiral's suite was reworked into accommodations for the Royal Family and their staff while the anti-aircraft mount on top of 'B' turret was replaced by a saluting platform. Agnew was promoted to rear-admiral with effect from 8 January 1947. The alterations were complete by December, and Vanguard made a shakedown cruise into the Central Atlantic and made a port visit to Gibraltar on the return voyage. Initially escorted by the destroyers Orwell, Obedient, Offa, Opportune, and Rotherham, the ship rendezvoused with the Home Fleet on 1 February 1947 to receive a 21-gun salute led by the battleships Nelson and Duke of York, and the aircraft carrier Implacable. Later that morning, a Sikorsky R-4 helicopter landed aboard to pick up mail and photographic film.

Vanguard arrived in Cape Town on 17 February, escorted by the South African frigates Good Hope, Transvaal and Natal on the last leg of her voyage. While the Royal Family toured the country on the first visit by a reigning monarch to South Africa, the ship exercised with ships of the South African and Royal Navies stationed there and made port visits to a number of South African cities. She sailed for home on 22 April and made brief visits to Saint Helena and Ascension Island en route. Vanguard arrived in Portsmouth on 11 May, and Captain F. R. Parham relieved the newly promoted Agnew on 29 May. In July, the ship began an overhaul in Devonport, which lasted until August 1948. While she was refitting, Vanguard was tasked to carry the Royal Family on a tour of Australia and New Zealand, planned for January 1949. On 31 August, she began a shakedown cruise to the Mediterranean and returned to Devonport on 12 November. Around this time, Vanguard was considered, along with a number of other large warships, for conversion to carry anti-aircraft missiles, but nothing further was done along these lines.

George VI was now too ill for travel, and the Royal Tour was indefinitely postponed later that month. Vanguard became the flagship of Admiral Sir Arthur Power, Commander-in-Chief of the Mediterranean Fleet, on 1 March 1949, and the ship made port visits to Algeria, France, Italy, Cyprus, Libya, Lebanon, Greece and Egypt before she arrived back at Devonport on 21 July. The newly promoted Rear Admiral Parham was relieved by Captain G. V. Gladstone a week later. The ship then became the flagship of the Home Fleet Training Squadron under Rear Admiral Edward Evans-Lombe on 12 November. While returning from a brief training sortie to Gibraltar, Vanguard went to the aid of a small French merchantman whose cargo had shifted in a severe storm on 13 February 1950. The merchantman, SS Boffa, was taken under tow and the cargo was redistributed. Once the storm had abated, Boffa was able to resume her voyage under her own power. Vanguard reached Weymouth Bay the following day. Later, in March, she fired the salute to Vincent Auriol, the President of France, during his state visit to Great Britain.

On 13 September 1950 Admiral Sir Philip Vian hoisted his flag as Commander in Chief, Home Fleet, on Vanguard and the ship joined the rest of Home Fleet on exercises with the Royal Canadian Navy and the Mediterranean Fleet. On 19 December, Vian transferred his flag to Indomitable. Nearly two months later, on 10 February 1951, the aircraft carrier collided with Vanguard as the carrier docked at Gibraltar. The hole in the battleship's stern was not serious, and Vian re-hoisted his flag in Vanguard shortly afterwards. After manoeuvres with Indomitable, during which her aircraft "sank" the battleship, the ship made port visits in Genoa and Villefranche-sur-Mer before returning for a brief refit in Devonport on 14 March. After completing her refit in May, she became flagship of the Home Fleet Training Squadron under Rear Admiral R. M. Dick at the Isle of Portland. Four months later the admiral transferred his flag to the carrier Indefatigable as Vanguard began another refit in preparation to again become the flagship of Home Fleet.

Buckingham Palace announced in November that King George VI was planning to take a short cruise for his health aboard Vanguard, which meant that her Admiral's suite again had to be modified to accommodate him and his staff. Captain John Litchfield assumed command on 21 December while the ship was still refitting, but the King died on 6 February 1952 before he could make his cruise. A detachment from the ship participated in his funeral procession before she departed for her post-refit shakedown cruise on 22 February. After exercising with Implacable, Indomitable and the fast minelayer Apollo, Vanguard returned home on 29 March. She became flagship of Home Fleet again on 13 May when Admiral Sir George Creasy hoisted his flag. Due to manning and weight problems, Vanguard operated with many of her turrets unmanned and with ammunition carried for only two of the 15-inch turrets and only starshell ammunition for the 5.25-inch guns. She participated in exercises with the Dutch and American navies, before returning to Portsmouth for the holidays. Litchfield was relieved by Captain R. A. Ewing on 19 January 1953; the ship departed the next day for a brief refit at Gibraltar. After its completion on 2 March, the ship trained with several of the Royal Navy's carriers before arriving back at Portsmouth on 25 March. Vanguard participated in Queen Elizabeth's Coronation Fleet Review at Spithead on 15 June 1953. The following September, she participated in NATO's Exercise Mariner in the Denmark Strait.

Admiral Sir Michael Denny replaced Creasy as Commander-in-Chief, Home Fleet, on 5 January 1954 and Vanguard participated in Exercise Medflex A with Dutch and French ships in March. During the rest of the year she participated in anti-submarine and anti-aircraft exercises as well as making port visits to Oslo and Kristiansand in Norway and Helsingborg in Sweden. She was inspected on 11 July by King Gustaf VI Adolf of Sweden before returning home later that month. Denny struck his flag on 15 September, and Vanguard sailed to Devonport for a £220,000 refit 10 days later. The February 1955 Defence Estimates had intended her as the Home Fleet flagship with a role as a Sverdlov-class cruiser killer, but after the appointment of Earl Mountbatten in April 1955 and with Antony Eden replacing Churchill as prime minister, the government decided instead to maintain two extra cruisers in the fleet, and Vanguard was placed in reserve when it completed its 1955 refit. She subsequently became the flagship of the Reserve Fleet when Vice Admiral Richard Onslow hoisted his flag on 28 November. While moored in Fareham Creek, during her time in the reserve fleet, waterline shots of Vanguard in Portsmouth Harbour were filmed for the title sequence of the 1957 comedy film Carry on Admiral. Just before decommissioning, scenes for the 1960 film Sink the Bismarck! were filmed aboard, with Vanguard being used to depict interiors of the bridges, Admiral's Quarters and gun turrets for Hood, Bismarck and King George V.

### Decommissioning and fate

On 9 October 1959 the Admiralty announced that Vanguard would be scrapped, as she was considered obsolete and too expensive to maintain. She was decommissioned on 7 June 1960 and sold to BISCO for £560,000. On 4 August 1960, when the ship was scheduled to be towed from Portsmouth to the breaker's yard at Faslane, Scotland, the whole of the Southsea sea front was packed with people who came to see her off. As Vanguard was being towed towards the harbour entrance, she slewed across the harbour and ran aground near the Still & West pub. She was pulled off by five tugboats an hour later, and after nearly running aground again near the Moving & East pub on the opposite shore, made her final exit from Portsmouth. Five days later she arrived at Faslane, and by mid-1962 the demolition process was complete. She was the last British battleship to be scrapped.

As a part of the scrapping process, sections of 150-millimetre-thick (5.9 in) pre-atomic steel plate uncontaminated with radionuclides were recovered from Vanguard and used for the shielding of the whole body monitor at the Radiobiological Research Laboratory (now DSTL) at Alverstoke, Gosport in Hampshire, England.

The process of decommissioning was filmed by the Rank Organisation for their Look at Life film series in an episode entitled The Last Battleship.

Fast British battleship

Cold War battleships of the United Kingdom