The air forces of the United Kingdom – the Royal Navy's Fleet Air Arm, the Army's Army Air Corps and the Royal Air Force use a roundel, a circular identification mark, painted on aircraft to identify them to other aircraft and ground forces. In one form or another, it has been used on British military aircraft from 1915 to the present.
Background
When the First World War started in 1914 it was the habit of ground troops to fire on all aircraft, friend or foe, so that the need for some form of identification mark became evident. At first the Union Flag was painted under the wings and on the sides of the fuselage. It soon became obvious that at a distance the St George's Cross of the Union Flag was likely to be confused with the Iron Cross that was already being used to identify German aircraft. After the use of a Union Flag inside a shield was tried it was decided to follow the lead of the French who used a tricolour cockade (a roundel of red and white with a blue centre). The British reversed the colours and it became the standard marking on Royal Flying Corps aircraft from 11 December 1914, although it was well into 1915 before the new marking was used with complete consistency. The official order stated:
The Royal Naval Air Service specified in A.I.D. SK. No. A78 a five-foot red ring with a white centre and a thin white outline on the lower surfaces of the lower wings at mid span, from October 1914 until it was decided to standardise on the RFC roundel for all British military aircraft in June 1915. With the same roundel being carried by RFC and RNAS aircraft, the use of the Union Jack was discontinued. The Royal Flying Corps and its successor the Royal Air Force have employed numerous versions of the roundel since then.
By 1917, a thin white outline was usually added to the roundel, to make the blue of the outer circle easier to distinguish from the dark PC.10 and PC.12 protective doping. On squadrons operating at night there was not the same need to make the marking more conspicuous, in fact it became customary to overpaint the white ring of the roundel itself – either in the camouflage finish of the aircraft as a whole, or in red. By the end of the war this had become standardised as the so-called "night roundel" of blue and red, that continued to be used on the dark NIVO green camouflage of post-war night bombers. Most RAF aircraft now had a silver finish (bare metal or aluminium doping) so that the national markings were conspicuous enough without outlining. During the late 1930s, RAF and Fleet Air Arm (FAA) aircraft were once again camouflaged, and a new outline was introduced, this time trainer yellow, and the same width as the blue and white rings.
Use by other air arms
Aside from the RAF, the Royal Navy's Royal Naval Air Service (First World War) and later the Fleet Air Arm, as well as the air elements of the British Army all adopted the same roundels.
Many nations that had been within the British Empire and Commonwealth continued to use British roundels despite having achieved independence, including Canada, Australia, New Zealand, and India until nationalism demanded unique roundels for each of those countries.
South Africa experimented with the four flag colours briefly, but then reverted to the RAF roundel but replaced the red with orange, and then the dot with a Springbok before replacing the disk with a five pointed castle.
In Canada, the Royal Canadian Air Force changed the red dot into a silver maple leaf, while the Royal Canadian Navy adopted the sugar maple leaf and both were replaced with a geometric stylized leaf.
Australia changed the red dot to a kangaroo (both standing and running were proposed before the running variant won out) and New Zealand experimented with gold, green and white ferns inset in the red dot before settling on a red kiwi.
India briefly replaced the SEAC roundel (blue on blue) with a blue and white chakra, before adopting an orange, white and green roundel.
Southern Rhodesia, the Federation of Rhodesia and Nyasaland and Rhodesia used variations on the British roundel featuring assegais before adopting a green ring with a lion and tusk on a white centre in 1970.
Roundel history
The use of letters (A, B, C, D) to denote different versions of roundels does not come from official documents, but rather from attempts by historians in the 1950s to catalogue the various roundels being used. Official documents instead provided dimensions in inches. Since most sources now use this nomenclature it has been included here.