World War 2 Stories for Sheffield

Anti-aircraft artillery
abv: Ack Ack
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 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.

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 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 Guided Weapon (SAGW).

Important non-English terms for air defence include German flak (from the German Fliegerabwehrkanone, aircraft defence cannon; also cited as Flugzeugabwehrkanone or Flugabwehrkanone) and the Russian term Protivovozdushnaya oborona (Cyrillic: Противовоздушная оборона), a literal translation of "anti-air defence", abbreviated as PVO. 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!"). In Russian all AA systems are called 'zenit' (zenith) systems (guns, missiles etc.). In French, air defence is called DCA (Défense Contre Avions).

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 practically usefully in itself as few AA guns are able to fire vertically, and maximum fuze 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 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". 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.

Hyde Park Anti-aircraft guns H 993

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. This means that projectiles either have to be guided to hit the target, or aimed at the predicted position of the target at the time the projectile reaches it, taking into account speed and direction of both the target and 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 computing (initially electromechanical analog computing from the 1930s on, as with equipment described below). 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 during the First World War 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 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 later called 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".

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 during the Second World War. 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.