The Royal Air Force, a much larger air force than America's at the time, used a two-digit code to denote a squadron and a third single letter to identify the aircraft within the squadron, said Howell. That system was impractical in combat, so by June 1943, the first tail system appeared.
The Square D became the official designation of the 3rd Air Division and the subordinate 100th Bombardment Group, who moved to RAF Mildenhall during the war. The Square D remains a symbol of the group’s legacy and their significant contribution to the allied victory in world war two. More