History of the 100th Air Refueling Wing and RAF Mildenhall
SQUARE “D” During World War II, bomb groups departing from England joined massive formations over the North Sea before heading to their targets on the continent. In order to ensure that members from the same group met and formed together, the bombers had tail markings unique to each bomb group. These consisted of a letter within a geometric shape to simplify recognition. These markings also enabled crews to identify each other when German antiaircraft defenses and fighters caused the formations to break apart. The B-17s of the 100th Bombardment Group bore the “Square D.”
2 100 ARW History Office