The existence of magnetism far out in space was
Degaussing is the method most used to reduce a
determined mathematically many years ago. The first
ship's magnetic field to minimize the distortion of the
factual proof came with the launching of the Explorer
earth's magnetic field. This, in turn, reduces the
and Pioneer satellites in 1958 and 1959. Radiation
possibility of detection by these magnetic sensitive
counters proved that the Van Allen belts, layers of
ordnances or devices.
high-intensity radiation existing far out in space,
followed the predicted magnetic contours.
Project Argus also gave additional proof of the
earth's magnetic field in space. In August of 1958, three
Upon completion of this chapter, you should be able
small 1.5-kiloton nuclear explosions were detonated
to do the following:
300 miles above the Falkland Islands in the South
1. Recognize the purpose of the degaussing
Atlantic. In the virtual vacuum that exists at 300 miles
above the earth's surface, free electrons, released by the
explosion, were captured by the earth's magnetic field.
2. Identify the various coils used in the degaussing
In less than 1 second, electrons spiralled from the
Southern to the Northern Hemisphere. Within an hour,
3. Identify the need for deperming.
they had covered the entire magnetic field at 300 miles
4. State the procedures used when ranging a ship.
5. Recognize the differences between the types of
Figure 10-1 shows the earth as a huge permanent
magnet, 6,000 miles long, extending from the Arctic to
the Antarctic polar region. Lines of force from this
6. Recognize the marking system used in
magnet extend all over the earth's surface, interacting
degaussing system installations.
with all ferrous materials on or near the surface. Since
A steel-hulled ship is like a huge floating magnet
many of these ferrous materials themselves become
with a large magnetic field surrounding it. As the ship
magnetized, they distort the background field into areas
moves through the water, this field also moves and adds
of increased or decreased magnetic strength. The lines
to or subtracts from the earth's magnetic field. Because
of magnetic force at the earth's surface do not run in
of its magnetic field, the ship can act as a triggering
device for magnetic-sensitive ordnance or devices.
Reduction of the ships static magnetic signature is
accomplished using the following means:
2. Nonmagnetic materials in construction
3. Controlling eddy current fields and stray
magnetic fields caused by various items of the
THE EARTH'S MAGNETIC
The magnetic field of the earth is larger than the
magnetic field of a ship. The earth's magnetic field acts
Figure 10-1.-Earth's magnetic field.
upon all metal objects on or near the earth's surface.