Combat codes : a full explanation and listing of British, Commonwealth and Allied air force unit codes since 1938

In 1938, with war looming, the RAF needed to introduce fresh security measures to protect its squadrons. Squadron markings were replaced by new two-letter unit codes which were applied to operational aircraft to help controllers but to confuse the enemy. Through the course of the war the system extended to Commonwealth and Allied air forces, including the USAAF. The system continued post-war and in a modified form is still in use today. Because of the need for secrecy the orders promulgating these codes were destroyed each time they were superseded and no official list exists. Through careful detective work the authors have produced, for the first time, a near-complete record of Allied unit codes.