A group is a military unit or a military formation that is most often associated with military aviation. Air and aviation groups The terms group and wing differ significantly from one country to another, as well as between different branches of a national defence force. Air groups vary considerably in size and status, but generally take two forms: A unit of two to four squadrons, commanded by a lieutenant colonel, colonel, commander, naval captain or an equivalent rank. The United States Air Force (USAF), groupes of the French Armée de l'air, gruppen of the German Luftwaffe, United States Marine Corps Aviation, British Fleet Air Arm and some other naval air services usually follow this pattern. A larger formation, often comprising more than 10 squadrons, commanded by a major general, brigadier general, commodore, rear admiral, air commodore or air vice-marshal. The air forces of many Commonwealth countries, such as the British Royal Air Force (RAF), follow this pattern. In such cases, the group is equivalent to a US wing, a German Geschwader or a French escadron. Historical overview During the early stages of World War I in France and Germany, the respective aviation services formed groupes and Gruppen. Beneath the level of the group was a unit of six to 16 aircraft: an escadrille or Staffel. Immediately above the French and German groups was the escadron or Geschwader. In the Royal Flying Corps (RFC) and Royal Naval Air Service (RNAS), a squadron was usually composed of 18–24 aircraft. When the Royal Air Force (RAF) was formed in 1918 from a merger of the RFC and RNAS, an officer with the rank of colonel typically commanded a group. The following year, when the RAF introduced its own rank system, RAF colonels became group captains, reflecting both the level of command responsibility and the seniority of naval captains (the equivalent Royal Navy rank). By World War II, the groupes of the French Armée de l'Air usually comprised two escadrilles (but sometimes only one, or as many as four). French groupes were the equivalent of U.S. Army Air Corps (USAAC) / U.S. Army Air Forces (USAAF) groups (analogous to RAF wings), while a groupement was the equivalent of a RAF group (USAAC/USAAF wing). For example, in May 1940 the Groupe de Bombardement I/31, a bomber unit, was operationally part of Groupement de Bombardement 6. In the German Luftwaffe, the principal unit of action was