Royal Air Force roundels

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.

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:

All aeroplanes of the RFC to be marked on the underside and on the rudder with concentric circles similar to those on the French machines but with the colours reversed, that is with a red circle inside a blue ring. The circles to be as large as possible. In addition a Union Jack 2 ft (0.61 m) x 1 ft 6 in (0.46 m) will be painted on the wing tips outside the circles.^{[citation needed]}

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 dope. On squadrons operating at night there was not the same need to make the marking more conspicuous, indeed 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, which continued to be used on the dark NIVO green camouflage of post-war night bombers. Most RAF aircraft now had a silver finish (either bare metal or aluminium dope) 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.

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 which 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.