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This is a description of what and why we have AA today.

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Anti-aircraft warfare

NATO defines air defence as "all measures designed to nullify or reduce the effectiveness of hostile air action."[1] They include ground and air based weapon systems, associated sensor systems, command and control arrangements and passive measures. It may be to protect naval, ground and air forces wherever they are. However, for most countries the main effort has tended to be 'homeland defence'. NATO refers to airborne air defence as counter-air and naval air defence as anti-aircraft warfare. Missile defence is an extension of air defence as are initiatives to adapt air defence to the task of intercepting potentially any projectile in flight.However, in some countries, such as Britain and Germany in World War II, the Soviet Union and NATO's European Command, ground based air defence and air defence aircraft have been under integrated command and control. Nevertheless, while overall air defence may be for homeland defence including military facilities, forces in the field, wherever they are, invariably deploy their own air defence capability if there is an air threat. A surface based air defence capability can also be deployed offensively to deny the use of airspace to an opponent.

Terminology The term air defence was probably first used by Britain when Air Defence of Great Britain (ADGB) was created as a Royal Air Force command in 1925. However, arrangements in UK were also called 'anti-aircraft', abbreviated as AA, a term that remained in general use into the 1950s. After World War I it was sometimes prefixed by 'Light' or 'Heavy' (LAA or HAA) to classify a type of gun or unit.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."[2] In some armies the term All-Arms Air Defence (AAAD) is used for air defence by non-specialist troops. Other terms from the late 20th century include GBAD (Ground Based AD) with related terms SHORAD (Short Range AD) and MANPADS ("Man Portable AD Systems": typically shoulder launched missiles). Anti-aircraft missiles are variously called surface-to-air missile, abbreviated and pronounced "SAM" and Surface to Air Guide Weapon (SAGW).Important non-English terms for air defence include German flak (from the German Fliegerabwehrkanone, aircraft defence cannon;[3] also cited as Flugzeug abwehr kanone) and the Russian term Protivovozdushnaya oborona (Cyrillic: Противовоздушная оборона), a literal translation of "anti-air defence", abbreviated as PVO.[4] Nicknames for anti-aircraft guns include AA, AAA or triple-A, an abbreviation of anti-aircraft artillery, "ack-ack" (from the World War I phonetic alphabet for AA), archie (a World War I British term probably coined by Amyas Borton and believed to derive via the Royal Flying Corps from the music-hall comedian George Robey's line "Archibald, certainly not!"[5]).The maximum distance at which a gun or missile can engage an aircraft is an important figure. However, many different definitions are used but 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'. Maximum ceiling being the height a projectile would reach if fired vertically, not very usefully particularly since few AA guns are able to fire vertically, furthermore maximum fuze length may be less than this. The British adopted "effective ceiling", meaning the altitude at which a gun could deliver a series or shells against a moving target, this could be constrained by maximum fuze running time as well as the gun's capability. By the late 1930s the British definition was "that height at which a directly approaching target at 400 mph can be engaged for 20 seconds before the gun reaches 70 degrees elevation".[6] However, effective ceiling for heavy AA guns was affected by non-ballistic factors:

  • The maximum running time of the fuze, this set the maximum usable time of flight.
  • The capability of fire control instruments to determine target height at long range.
  • The precision of the cyclic rate of fire, the fuze length had to be calculated and set for where the target would be at the time of flight after firing, to do this meant knowing exactly when the round would fire.

General Description

The essence of air defence is to detect hostile aircraft and destroy them. The critical issue is to hit a target moving in three dimensions, which means the attack has to be in four dimensions to put the munition in the right place at the right time. This means that either projectiles have to be guided to hit the target or aimed ahead of the target by estimating, or predicting, their future position at the time of firing plus time of flight of the projectile.Throughout the 20th Century air defence was one of the fastest evolving areas of military technology, responding to the evolution of aircraft and exploiting various enabling technologies, particularly radar, guided missiles and computers. Air defence evolution covered the areas of sensors and technical fire control, weapons, and command and control. At the start of the 20th Century these were either very primitive or non-existent.Initially sensors were optical and acoustic devices developed in World War I and continued into the 1930s, but were quickly superseded by radar, which in turn was supplemented by optronics in the 1980s.Command and control remained primitive until the late 1930s, when Britain created an integrated system[7] for ADGB that linked the ground-based air defence of the army's AA Command, although field deployed air defence relied on less sophisticated arrangements. NATO calls these arrangements an "air defence ground environment", defined as "the network of ground radar sites and command and control centres within a specific theatre of operations which are used for the tactical control of air defence operations".[1]Rules of Engagement are critical to prevent air defences engaging friendly or neutral aircraft. Their use is assisted but not governed by IFF (identification friend or foe) electronic devices originally introduced in World War II. While these rules originate at the highest authority, different rules can apply to different types of air defence covering the same area at the same time. AAAD usually operates under the tightest rules.NATO calls these rules Weapon Control Orders (WCO), they are:

  • weapons free: a weapon control order imposing a status whereby weapons systems may be fired at any target not positively recognized as friendly.
  • weapons hold: a weapon control order imposing a status whereby weapons systems may only be fired in self-defence or in response to a formal order.
  • weapons tight: a weapon control order imposing a status whereby weapons systems may be fired only at targets recognized as hostile.[1]

Until the 1950s gun fired munitions were the norm, guided missiles then became dominant, except at the very shortest ranges. However, the type of shell or warhead and its fuzing, and with missiles the guidance arrangement, were and are varied. Targets are not always easy to destroy, although damaged aircraft may be forced to abort their mission and if reaching their base may be out of action for days or even scrapped. Ignoring small arms, ground based air defence guns have varied in calibre from 20 mm to at least 149 mm.[8]Ground based air defence is deployed in several ways:

  • Self-defence by ground forces using their organic weapons, AAAD.
  • Accompanying defence, specialist aid defence elements accompanying armoured or infantry units.
  • Point defence around a key target, such as a bridge, critical government building or ship.
  • Area air defence, typically 'belts' of air defence to provide a barrier, but sometimes an umbrella covering an area. Areas can vary widely in size, belts along a nation's border, e.g. the Cold War MIM-23 Hawk and Nike belts that ran north–south across Germany, a military formation's manoeuvre area, or the area of a city or port. In ground operations air defence areas may be used offensively by rapid redeployment across current aircraft transit routes.

Air defence has included other elements, although after World War II most fell into disuse:

  • Tethered Barrage Balloons to deter and prevent aircraft flying below the height of the balloons.
  • Searchlights to illuminate aircraft at night for both gun layers and optical instrument operators. During World War II searchlights became radar controlled.
  • Smoke, large smoke screens created by large smoke canisters on the ground to screen targets and prevent accurate weapon aiming by aircraft.

Passive air defence is defined by NATO as "Passive measures taken for the physical defence and protection of personnel, essential installations and equipment in order to minimize the effectiveness of air and/or missile attack".[1] It remains a vital activity by ground forces and includes camouflage and concealment to avoid detection by reconnaissance and attacking aircraft. Measures such as camouflage painting important buildings was common in World War II. During the Cold War some airfields painted their runways and taxiways green.

Information supplied by wikipedia

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