A Kōkūtai (航空隊) was, during World War II and in the Imperial Japanese Navy, a type of aerial combat unit, similar to the Air Groups in service in the other armies and navies of the time (called "Group" in the British Royal Air Force, Gruppe in the German Luftwaffe, Groupe in the French Armée de l'Air etc.). Although belonging to the Imperial Navy the Japanese Kōkūtai could be based at land or on board of carriers and were constituted by hundreds of men and aircraft (that latters were distributed in smaller units called Hikōtai, the equivalent of squadrons). For example, the famous 343 Kōkūtai (a fighter group, divided in three Hikōtai) was based at land while the 652nd Kōkūtai (a bomber group) was carrier-based. As in general in the Imperial Japanese Navy Air Service, most pilots and aircrew members of a Kōkūtai were non-commissioned officers.
The word Kōkūtai is abbreviated with the abbreviation "Ku". 343 Ku, for example, stands for 343 Kōkūtai.
In the Imperial Japanese Navy Air Service (IJNAS), a Kōkūtai was the equivalent of an Air Group. In the Imperial Japanese Army Air Service (IJAAS) the equivalent unit was the Sentai. The term "Sentai", as a unit, was in use in the IJNAS, but it designated a larger unit than the IJAAS Sentai or the IJNAS Kōkūtai.