Most units of the Royal Air Force (RAF) are identified by a two character alphabetical or alpha- numeric combination squadron code. Usually, that code is painted on the aircraft belonging to that unit. The squadron code is usually presented along with an individual letter or character to form a call sign for the particular aircraft. Location of the call sign combination has usually been on the rear fuselage next to the RAF roundel. In instances when an unusually large numbers of aircraft comprise the squadron, multiple squadron codes have been used. Other air forces, especially those from other Commonwealth countries, have often used similar systems of identification. During the Second World War, when units from other air forces were attached to the RAF – such as the Article XV squadrons (also known as "400 series squadrons") – their squadron codes were often changed, to avoid confusion with RAF units. Squadron codes A-E F- J K-O P-T U-Z Numbers * = RAAF/RCAF unit that was not under RAF operational control. Radio call signs Transport Command 'O' series Transport Command RAF applied the following three letter call-signs to its aircraft from 1944. Individual aircraft were given letter suffixes, making the code a four letter sequence. Transport Command 'MO' series From 1945 RAF Transport Command pre-fixed the three letter call-signs with M. With individual aircraft allocated letter suffixes, the call-signs became five letter sequences. Data from: See also Royal Air Force List of Royal Air Force aircraft squadrons List of Royal Air Force aircraft independent flights List of conversion units of the Royal Air Force List of Royal Air Force Glider units List of Royal Air Force Operational Training Units List of Royal Air Force schools List of Royal Air Force units & establishments List of RAF squadron codes List of RAF Regiment units List of Battle of Britain squadrons List of wings of the Royal Air Force Royal Air Force roundels Army Air Corps List of Army Air Corps aircraft units Fleet Air Arm List of Fleet Air Arm aircraft squadrons List of Fleet Air Arm groups List of aircraft units of the Royal Navy List of aircraft wings of the Royal Navy Others List of Air Training Corps squadrons University Air Squadron Air Experience Flight Volunteer Gliding Squadron United Kingdom military aircraft serial numbers United Kingdom aircraft test serials British military aircraft designation systems References Citations Bibliography Further reading Bowyer, Michael