Why anti-aircraft fire is called flak, ack-ack and archie
Air defence has collected a remarkable set of nicknames. Flak shortens a German word for aircraft-defence cannon, ack-ack comes from the British signallers' way of saying AA, and archie reportedly began as a music-hall joke. Behind the slang lies a hard problem: hitting something moving in three dimensions before it gets away.
Archie was a First World War British term, probably coined by Amyas Borton and traced through the Royal Flying Corps to a comedian's catchphrase, "Archibald, certainly not!" In Russian, air defence systems are called zenitnye, meaning pointed at the zenith. The phrase air defence itself probably began in Britain in 1925, when the Royal Air Force created a command called Air Defence of Great Britain.
The core difficulty is timing. A shell or missile must reach the same point in space as the aircraft at the same moment, so gunners either guide the weapon onto the target or aim at where it will be, accounting for the speed and heading of both. By the late 1930s, British planners defined a gun's effective ceiling as the height at which it could engage a target approaching at 400 miles per hour for 20 seconds before the barrel reached 70 degrees of elevation. Guns firing everything from rifle-calibre rounds to 6-inch shells were standard until the 1950s, when guided missiles took over except at the shortest ranges.
Few military fields changed faster during the 20th century. Early warning relied on optical and acoustic listening devices from the First World War until radar replaced them, later supplemented by optoelectronics in the 1980s. Britain's Dowding system in the late 1930s tied radar, fighters and ground guns into one network. Other methods faded after 1945: barrage balloons whose steel tethers threatened low-flying planes, cables strung across valleys, searchlights and vast smoke screens. Camouflage survived; during the Cold War some airfields painted their runways green.
Avoiding friendly fire is as important as hitting enemies. NATO's rules run from weapons free, allowing fire at anything not identified as friendly, through weapons tight, requiring positive identification as hostile, to weapons hold, meaning fire only in self-defence or on order. Organisation varies: the Soviet Union ran air defence as a fully separate service with its own fighters, while Japan and Israel place ground-based systems within their air forces.
Source: Anti-aircraft warfare
