The zone of immunity (or immunity zone) around a
warship
A warship or combatant ship is a naval ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces of a state. As well as being armed, warships are designed to withstand damage and are usually faster ...
is an area from which both
plunging fire and direct enemy fire is less effective.
The concept was a factor in battleship design and in tactics during engagements.
ADM 239/268: C.B.04039, ARMOUR PROTECTION (1939)
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Background
Warships traditionally have vertical, or near vertical, belt armour
Belt armor is a layer of heavy metal armor plated onto or within the outer hulls of warships, typically on battleships, battlecruisers and cruisers, and aircraft carriers.
The belt armor is designed to prevent projectiles from penetrating to ...
which protects against missile
In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocke ...
s (shells) travelling horizontally, and horizontal deck armour, which protects against plunging (downward) shell fire. Belt armour is generally thicker than deck armour.
A shell fired at short range will travel at a high velocity on a more or less horizontal trajectory. If it strikes a ship it will do so either at an acute angle
In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle.
Angles formed by two rays lie in the plane that contains the rays. Angles ar ...
to the belt armour or an oblique angle to the deck armour.
A shell fired at long range will travel on a ballistic trajectory
Projectile motion is a form of motion experienced by an object or particle (a projectile) that is projected in a gravitational field, such as from Earth's surface, and moves along a curved path under the action of gravity only. In the part ...
, arriving at its target at a steep angle of descent and so strike the deck armour although at a velocity markedly less than its original muzzle velocity.
If a ship is too close to an adversary, shells fired horizontally may pierce inadequate vertical armour; beyond a certain range, determined by the kinetic energy of incoming projectiles, plunging shells will penetrate deck armour. The distance between these two situations, which is determined by the energy of incoming ordnance and the thickness of the armour of the target vessel, is known as the zone of immunity.
See also
*Sloped armour
Sloped armour is armour that is neither in a vertical nor a horizontal position. Such angled armour is typically mounted on tanks and other armoured fighting vehicles (AFVs), as well as naval vessels such as battleships and cruisers. Sloping an ...
References
Sources
*{{cite book , first=Norman , last=Friedman , year=1985 , title=U.S. Battleships: An Illustrated Design History , publisher=Naval Institute Press , isbn=0-87021-715-1
External links
*http://www.navweaps.com/index_tech/tech-069.htm
Naval warfare
Naval armour