Anti-aircraft warfare

Anti-aircraft warfare (AAW) or air defence (or air defense in American English) is the counter to aerial warfare and includes "all measures designed to nullify or reduce the effectiveness of hostile air action". It encompasses surface-based, subsurface (submarine-launched), and air-based weapon systems, in addition to associated sensor systems, command and control arrangements, and passive measures (e.g. barrage balloons). 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 optimised for short-, medium-, or long-range air defence, although some systems may incorporate multiple weapons (such as both autocannons and surface-to-air missiles). 'Layered air defence' usually refers to multiple 'tiers' of air defence systems which, when combined, an airborne threat must penetrate to reach its target; this defence is usually accomplished via the combined use of systems optimised for either short-, medium-, or long-range air defence.

In some countries, such as Britain and Germany during the Second World War, the Soviet Union, and modern NATO and the United States, ground-based air defence and air defence aircraft have been under integrated command and control. 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 1950s, guns firing ballistic munitions ranging from 7.62 mm (.30 in) to 152.4 mm (6 in) were the standard weapons; guided missiles then became dominant, except at the very shortest ranges (as with close-in weapon systems, which typically use rotary autocannons or, in very modern systems, surface-to-air adaptations of short-range air-to-air missiles, often combined in one system with rotary cannons).

It may also be called counter-air, anti-air, AA, flak, layered air defence or air defence forces.

The term air defence was probably first used by the UK when Air Defence of Great Britain (ADGB) was created as a Royal Air Force command in 1925. However, arrangements in the UK were also called anti-aircraft, abbreviated as AA, a term that remained in general use into the 1950s. After the First World War it was sometimes prefixed by "light" or "heavy" (LAA or HAA) to classify a type of gun or unit. 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". In some armies the term all-arms air defence (AAAD) is used for air defence by nonspecialist troops. Other terms from the late 20th century include "ground based air defence" (GBAD) with related terms "short range air defence" (SHORAD) and man-portable air-defence system (MANPADS). Anti-aircraft missiles are variously called surface-to-air missiles, ("SAMs") and surface-to-air guided weapons (SAGWs). Examples are the RIM-66 Standard, Raytheon Standard Missile 6, or the MBDA Aster missile.

Non-English terms for air defence include the German term Flak or FlaK (Fliegerabwehrkanone, lit. 'aircraft defence cannon', also cited as Flugabwehrkanone), and the Russian term Protivovozdushnaya oborona (Russian: Противовозду́шная оборо́на, lit. 'anti-air defence'), abbreviated as PVO. In Russian, the AA systems are called zenitnye (i.e., 'pointing to zenith') systems. In French, air defence is called Défense contre les aéronefs (DCA) , lit. 'defence against aircraft'.