Anti-aircraft warfare is the counter to aerial warfare [ 1 ] and includes "all measures designed to nullify or reduce the effectiveness of hostile air action". It may be used to protect naval , ground , and air forces in any location. However, for most countries, the main effort has tended to be homeland defence. Missile defence is an extension of air defence, as are initiatives to adapt air defence to the task of intercepting any projectile in flight.
Most modern anti-aircraft AA weapons systems are optimized for short-, medium-, or long-range air defence, although some systems may incorporate multiple weapons such as both autocannons and surface-to-air missiles. However, while overall air defence may be for homeland defence including military facilities , forces in the field, wherever they are, provide their own defences against airborne threats.
Until the s, guns firing ballistic munitions ranging from 7. It may also be called counter-air , anti-air , AA , flak , layered air defence or air defence forces. However, arrangements in the UK were also called anti-aircraft , abbreviated as AA , a term that remained in general use into the s. Nicknames for anti-aircraft guns include:. NATO defines anti-aircraft warfare AAW as "measures taken to defend a maritime force against attacks by airborne weapons launched from aircraft, ships, submarines and land-based sites".
The maximum distance at which a gun or missile can engage an aircraft is an important figure. However, many different definitions are used and unless the same definition is used, performance of different guns or missiles cannot be compared. For AA guns only the ascending part of the trajectory can be usefully used. One term is "ceiling", the maximum ceiling being the height a projectile would reach if fired vertically, not practically useful in itself as few AA guns are able to fire vertically, and the maximum fuse duration may be too short, but potentially useful as a standard to compare different weapons.
The British adopted "effective ceiling", meaning the altitude at which a gun could deliver a series of shells against a moving target; this could be constrained by maximum fuse running time as well as the gun's capability. The essence of air defence is to detect hostile aircraft and destroy them. The critical issue is to hit a target moving in three-dimensional space; an attack must not only match these three coordinates, but must do so at the time the target is at that position.
