A flight is a small military unit within the larger structure of an air force, naval air service, or army air corps; and is usually subordinate to a larger squadron. A military aircraft flight is typically composed of four aircraft, though two to six aircraft may also form an aircraft flight; along with their aircrews and ground staff. In some very specific examples, typically involving historic aircraft, a flight may contain as many as twelve aircraft, as is the case with the Battle of Britain Memorial Flight (BBMF) of the Royal Air Force (RAF) in the United Kingdom. In most usages, two or more flights make up a squadron.