The Imperial Japanese Navy Air Service was under the control of the Navy Aviation Bureau (Kaigun Kōkū Hombu) . Administrative Organizations Kōkū Kantai Kōkū Kantai (air fleet) contained one or more kōkū sentai. The most notable kōkū kantai was the First Air Fleet containing Japan's six fleet carriers and was responsible for the attack on Pearl Harbor. IJN also maintained a land-based system of naval air fleets and area air fleets called homen kantai containing mostly twin-engine bombers and seaplanes. Kōkū Sentai Kōku Sentai (air flotillas) consisted of two or more Kōkūtai, they were commanded by Rear Admirals. Kōkū sentai contained anywhere from a handful to 80 or 90 aircraft, and were dependent on both the mission and type of aircraft carrier or air station that they were located on. A kōku sentai was equivalent to a carrier division and contained all carrier aircraft within the division. The first kōku sentai, in December 1941, consisted of all aircraft aboard the carriers and . While the land-based kōku sentai consisted of 3 kokutais. Kōkūtai Kōkūtai (air group) was equivalent to a group or wing. A kōkūtai in the broadest terms could comprise a flight and base element of either a carrier or land-based air group. In terms of the flight element, it was generally composed of 18 to 27 aircraft and took the name of the carrier or air station where it was originally formed. It could also be either homogeneous or composed of different types of aircraft. The land-based units had larger numbers of aircraft, and could number from approximately 24 to a 100 or more aircraft. They were more homogeneous and came under the command of the naval district where their home naval air station was located in, and later were designated either by a number or by the name of that particular station. There were over 90 naval air groups at the start of the Pacific War. Kōkūtai was led by its Commander (Shirei) and its Air Officer (Hikōchō), where the latter typically had the role of executive officer. The flight element of kōkūtai was called hikōtai and was led by Hikōtaichō. The non-flight element of kōkūtai was composed of ground units that provided aircraft maintenance and air base service functions. The land-based Kōkūtai system was set up in 1916, determined that naval air stations and air groups would be organized as needed, at either naval ports (gunkō)