A group is a military aviation unit, a component of military organization and a military formation. Usage of the terms group and wing differ from one country to another, as well as different branches of a defence force, in some cases. Groups therefore vary considerably in size. In many air services, a group is made up of two to four squadrons and is usually commanded by a Lieutenant Colonel, Commander or an officer of equivalent rank. In France and Germany, the precursors of the Armée de l’Air and Luftwaffe formed groupes and Gruppen during the early stages of World War I. The groups of the Armée de l’Air usually comprise two escadrons, but sometimes only one, or as many as four. Three German Staffeln (similar to the English language concept of “squadrons”) make up a Gruppe. In the United States Air Force (USAF) a group may consist of two or more squadrons. Prior to 1991, it was not unusual for a USAF support group to have no subordinate squadrons, but merely be a larger unit than a squadron. In such cases the group would not have a headquarters. Similarly, in the British Fleet Air Arm and some other naval air services, a group usually consists of three squadrons. In the United States Marine Corps, a group consists of at least two squadrons. Two or more groups form a wing. In the British Royal Air Force (RAF) and the air forces of many Commonwealth countries, a group is made up of several wings, each of which controls two or more squadrons, so that a group normally includes six to 10 squadrons, and is thus equivalent to a USAF wing. It is also roughly equivalent to the “carrier air groups” formerly deployed by the United States Navy (USN), although the term is no longer used by the USN. RAF stations (air bases) are also controlled by a particular group, although Expeditionary Air Groups control expeditionary air wings directly. Groups are directly subordinate to a command (or, historically, to a tactical air force). When the RAF was formed, an officer with the rank of Group Captain (equivalent to Colonel and (Navy) Captain) commanded such a unit, although by the time of World War II, some groups were commanded by Air Commodores (equivalent to Brigadiers/Brigadier Generals and Commodores) or even Air Vice-Marshals (equivalent to Major Generals and Rear Admirals).