The , also known as the Kidō Butai ("Mobile Force"), was a combined carrier battle group comprising most of the aircraft carriers and carrier air groups of the Imperial Japanese Navy (IJN) during the first eight months of the Pacific War.
At the time of its attack on Pearl Harbor, in December 1941, the 1st Air Fleet was the world's largest fleet of aircraft carriers.
In its second generation, 1st Air Fleet was a land-based fleet of "kichi kōkūtai" (base air unit[s]).
Origins
In 1912, the British Royal Navy had established its own flying branch, the Royal Naval Air Service (RNAS). The IJN was modeled on the Royal Navy and the IJN Admiralty sought establishment of their own Naval Air Service. The IJN had also observed technical developments in other countries and saw military potential of the airplane. In 1913, the IJN seaplane carrier Wakamiya was converted into a seaplane tender and aircraft were purchased. The 1st and 2nd Air Fleet were to be the primary attack force of the IJNAS.
The Japanese carriers' experiences off China had helped further develop the IJN's carrier doctrine. One lesson learned in China was the importance of force concentration and mass in projecting naval air power ashore. Therefore, in April 1941 the IJN formed the 1st Air Fleet to combine all of its fleet carriers under a single command. The IJN centered its doctrine on air strikes that combined the air groups within carrier divisions, rather than each individual carrier. When more than one carrier division was operating together, the divisions' air groups were combined with each other. This doctrine of combined, massed, carrier air attack groups was the most advanced of its kind of all the world's navies. The IJN, however, remained concerned that concentrating all of its carriers together would render them vulnerable to being wiped out all at once by a massive enemy air or surface strike. Thus, the IJN developed a compromise solution in which the fleet carriers would operate closely together within their carrier divisions but the divisions themselves would operate in loose rectangular formations, with approximately separating the carriers from each other.Parshall and Tully, pp. 82, 86, 137–138, and 416; Peattie, pp. 124–25, 147–53; Tully; Stille, pp. 13–14According to Parshall and Tully, pp. 86–87, the Japanese would not usually launch their entire carrier air groups into a single massed attack. Instead, each carrier would launch a "deckload strike" of all its aircraft that could be spotted at one time on each flight deck. Subsequent attack waves consisted of the next deckload of aircraft. Thus, 1st Air Fleet air attacks would often consist of at least two, massed waves of aircraft. Peattie (p. 152) and Jisaburō Ozawa (Goldstein, pp. 78–80) emphasize that the First Air Fleet was not the IJN's primary strategic striking force. The IJN still considered the First Air Fleet an integral component in the Combined Fleet's decisive battle task force centered on battleships.
Although the concentration of so many fleet carriers into a single unit was a new and revolutionary offensive strategic concept, the First Air Fleet suffered from several defensive deficiencies which gave it, in Mark Peattie's words, a glass jaw': it could throw a punch but couldn't take one."Peattie, p. 159 Japanese carrier anti-aircraft guns and associated fire control systems had several design and configuration deficiencies which limited their effectiveness. The IJN's fleet combat air patrol (CAP) consisted of too few fighter aircraft and was hampered by an inadequate early warning system, including a lack of radar. Poor radio communications with the fighter aircraft inhibited effective command and control of the CAP. The carriers' escorting warships were deployed as visual scouts in a ring at long range, not as close anti-aircraft escorts, as they lacked training, doctrine, and sufficient anti-aircraft guns. These deficiencies would eventually doom Kaga and other First Air Fleet carriers.Parshall and Tully, pp. 85 and 136–145; Peattie, pp. 155–59: Stille, pp. 14–15, 50–51
Organization
As a Carrier-Based Fleet
The First Air Fleet (Dai-ichi Kōkū Kantai) was a major component of the Combined Fleet (Rengō Kantai). When created on 10 April 1941, it had three kōkū sentai (air flotillas; in the case of aircraft carriers, carrier divisions): On that date, First Kōkū Sentai consisted of and and their aircraft units. Later that spring, a number of destroyers were added. On 10 April 1941, Second Kōkū Sentai comprised , and the 23rd Kuchikutai (Destroyer Unit). Fourth Kōkū Sentai consisted solely of light carrier and her aircraft unit, until two destroyers were added in August. (At its inception, First Air Fleet did not include Third Kōkū SentaiPrange, Gordon W. in collaboration with Goldstein, Donald M. and Dillon, Katherine V. (1981) At Dawn We Slept: The Untold Story of Pearl Harbor, Penguin Books, Ltd., p. 101 and it did not include it on 7 December 1941. Third Kōkū Sentai (3rd Carrier Division, see table below) was attached to First Fleet, as distinct from First Air Fleet.Thorpe, Donald W. (1977) Japanese Naval Air Force Camouflage and Markings World War II, Aero Publishers, Inc., p. 116 On 1 April 1942, Third Kōkū Sentai was disbanded.Imperial Flattops) See the table titled "Transition", below.
When formed on 10 April 1941, First Air Fleet was a naval battlegroup with the single most powerful concentration of carrier-based aircraft in the world at the time.Tully, Anthony, "Stories and Battle Histories of the IJN's Carrier Fleet", Retrieved 8 September 2010. Military historian Gordon Prange called it "a revolutionary and potentially formidable instrument of sea power."Prange, Gordon W. in collaboration with Goldstein, Donald M. and Dillon, Katherine V. (1981). At Dawn We Slept: The Untold Story of Pearl Harbor, Penguin Books, Ltd., p. 107
Fifth Kōkū Sentai (5th Carrier Division) was created on 1 September 1941 and was added to First Air Fleet The Naval Data Base:航空戦隊.. When the new aircraft carrier was added to Fifth Kōkū Sentai, First Air Fleet consisted of Akagi, Kaga, Sōryū, Hiryū, Ryūjō, Kasuga Maru (renamed ca. 31 August 1942), and Zuikaku, along with their aircraft units and a number of destroyers. On 25 September 1941, Kasuga Maru was transferred from Fifth Kōkū Sentai to Fourth Kōkū Sentai.Imperial Flattops (Kasuga Maru was used to ferry aircraft to distant Japanese bases and should not be considered a front-line aircraft carrier. The status of any aircraft unit that she may have had is unclear.Imperial Flattops) Light carrier was added to Fourth Kōkū Sentai on 22 December 1941.Imperial lattops She was destroyed on 7 May 1942 in the Battle of the Coral Sea.Imperial lattops Akagi, Kaga, Sōryū, and Hiryū were lost in the Battle of Midway.Morison, Samuel Eliot (1963). The Two-Ocean War, Little, Brown & Co., ff. 156–161
Each Kōkū Sentai of First Air Fleet tended to include a pair of aircraft carriers, and each included the respective hikōkitai/hikōtai (aircraft/aviation unit(s)) of each aircraft carrier.Hata, Ikuhiko; Izawa, Yasuho and Shores, Christopher (2011). Japanese Naval Air Force Fighter Units and Their Aces 1932–1945, Grub Street, ff. 128–159, Thorpe, Donald W., (1977). Japanese Naval Air Force Camouflage and Markings World War II, Aero Publishers, Inc., Each Kōkū Sentai of First Air Fleet was a tactical unit that could be deployed separately or combined with other Kōkū Sentai of First Air Fleet, depending on the mission. For example, for operations against New Britain and New Guinea in January 1942, First Kōkū Sentai and Fifth Kōkū Sentai participated.Hata, Ikuhiko; Izawa, Yasuho and Shores, Christopher (2011). Japanese Naval Air Force Fighter Units and Their Aces 1932–1945, Grub Street, p. 21,
The number (from approximately two dozen up to approximately 80 aircraft) and type of aircraft varied, based on the capacity of the aircraft carrier.IJN 1st Air Fleet Retrieved 8 September 2010. The large fleet carriers had three types of aircraft; fighters, level/torpedo bombers, and dive bombers. The smaller carriers tended to have only two types of aircraft, fighters and torpedo bombers.
At the beginning of the Pacific War, First Air Fleet included six fleet carriers: Akagi, Kaga, Sōryū, Hiryū, Shōkaku, and Zuikaku, and two light carriers: Ryūjō and Kasuga Maru (later renamed Taiyō), as shown in the table below.
On 14 July 1942, First Air Fleet was converted into Third Fleet (第三艦隊) and Eighth Fleet (第八艦隊), and 2nd Carrier Division (first generation) and 5th Carrier Division were disbanded.Nairei (Internal Order) No. 1241, 14 July 1942, amending Nairei No. 1226 of 1941, JACAR (アジア歴史資料センター Asia Historical Materials Center) Ref.C12070164100, page 9 of 50. On the same date, the Japanese Navy's front-line aircraft carriers and their aircraft units came under the command of the 3rd Fleet, which was created in its sixth generation on that date.戦史叢書80巻463-465頁「空母部隊の再建と新戦法」(Senshi Sōsho Vol. 80, ff.463-465; "Rebuilding Carrier Units and New Tactics".
The (機動部隊, Mobile Strike Force) was the Combined Fleet's tactical term for its combined carrier battle groups. The title was used as a term of convenience; it was not a formal name for the organization. It consisted of Japan's six largest carriers, carrying the 1st Air Fleet. This mobile task force was created for the attack on Pearl Harbor under Vice-Admiral Chūichi Nagumo in 1941.Parshall and Tully, pp. 6 & 535. For the attack, the Kidō Butai consisted of six aircraft carriers (commanded by Chūichi Nagumo, Tamon Yamaguchi and Chūichi Hara) with 414 airplanes, two battleships, three cruisers, nine destroyers, eight tankers, 23 submarines, and four midget submarines. These escort ships were borrowed from other fleets and squadrons. It was the most powerful naval fleet until four of the six aircraft carriers of the unit were destroyed in the disastrous Battle of Midway.
Carriers of the Kidō Butai, 1941 1st Carrier Division 2nd Carrier Division 3rd Carrier Division 4th Carrier Division 5th Carrier Division
Transition (extract) Date Lower units Lowest units and ships 10 April 1941 (original) 1st Carrier Division , Destroyer Division 7: , 2nd Carrier Division , Destroyer Division 23: , 4th Carrier Division 10 December 1941 1st Carrier Division Akagi, Kaga Destroyer Division 7: Akebono, Ushio 2nd Carrier Division Sōryū, Hiryū Destroyer Division 23: Kikuzuki, Uzuki 4th Carrier Division Ryūjō, Destroyer Division 3: , 5th Carrier Division , , , 10 April 1942 1st Carrier Division Akagi, Kaga 2nd Carrier Division Hiryū, Sōryū 4th Carrier Division Ryūjō, 5th Carrier Division Shōkaku, Zuikaku 10th Cruiser-Destroyer Squadron Destroyer Division 4: , , , Destroyer Division 10: , , , Akigumo Destroyer Division 17: , , , 14 July 1942 disbanded
Commanders
Commander-in-Chief
Chief of Staff
As a Land-Based Air Fleet