The United States Army, United States Navy, United States Marine Corps, United States Air Force and its predecessors, and United States Coast Guard operated aircraft when specific alphanumerical designation systems were not in use; these aircraft were referred to by their manufacturers' designations. There were also aircraft in service later that did not receive designations for other reasons, such as foreign military aircraft used for testing or special operations, and civil aircraft purchased off-the-shelf or impressed into service.
