1st Air Fleet (IJNAS)
第一航空艦隊 (Daiichi Kōkū Kantai)
Rising Sun Flag
Active	10 April 1941 – 14 July 1942 1 June 1943 – 15 June 1945
Country	Empire of Japan
Allegiance	Emperor of Japan
Branch	Imperial Japanese Navy
Type	Naval Air Fleet (Kantai)
Engagements	Pacific War Pearl Harbor Wake Island Rabaul Darwin Indian Ocean Coral Sea Midway Eastern Solomons Santa Cruz Philippine Sea Leyte Gulf
Commanders
Notable commanders	Chūichi Nagumo
Insignia
Roundel

The1st Air Fleet (第一航空艦隊,Daiichi Kōkū Kantai), also known as theKidō Butai ("Mobile Force"), was a combinedcarrier battle group comprising most of theaircraft carriers andcarrier air groups of theImperial Japanese Navy (IJN) during the first eight months of thePacific War.

At the time of its best-known operation, theattack 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)).

In 1912, the BritishRoyal Navy had established its own flying branch, theRoyal 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, theIJN seaplane carrierWakamiya was converted into aseaplane tender and aircraft were purchased. The 1st and 2nd Air Fleet were to be the primary attack force of theIJNAS.

The Japanese carriers' experiences off China had helped further develop the IJN's carrier doctrine. One lesson learned in China was the importance offorce 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 7,000 metres (7,700 yd) separating the carriers from each other.^{[1][Note 1]}

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, inMark Peattie's words, a"'glass jaw': it could throw a punch but couldn't take one."^[2] Japanese carrieranti-aircraft guns and associated fire control systems had several design and configuration deficiencies which limited their effectiveness. The IJN's fleetcombat air patrol (CAP) consisted of too few fighter aircraft and was hampered by an inadequate early warning system, including a lack ofradar. 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 doomKaga and other First Air Fleet carriers.^[3]

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The First Air Fleet(Dai-ichi Kōkū Kantai) was a major component of theCombined 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 ofAkagi andKaga and their aircraft units. Later that spring, a number of destroyers were added. On 10 April 1941, Second Kōkū Sentai comprisedSōryū,Hiryū and the 23rd Kuchikutai (Destroyer Unit). Fourth Kōkū Sentai consisted solely oflight carrierRyūjō and her aircraft unit, until two destroyers were added in August. (At its inception, First Air Fleet did not include Third Kōkū Sentai^[4] 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.^[5] 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.^[6] Military historianGordon Prange called it "a revolutionary and potentially formidable instrument of sea power."^[7]

Fifth Kōkū Sentai (5th Carrier Division) was created on 1 September 1941 and was added to First Air FleetThe Naval Data Base:航空戦隊.. When the new aircraft carrierZuikaku was added to Fifth Kōkū Sentai, First Air Fleet consisted ofAkagi,Kaga,Sōryū,Hiryū,Ryūjō,Kasuga Maru (renamedTaiyō ca. 31 August 1942),Shōkaku andZuikaku,^{[8][9][10][11][12][13][14][15]} along with their aircraft units and a number of destroyers.The Naval Data Base:航空戦隊. 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 carrierShōhō was added to Fourth Kōkū Sentai on 22 December 1941.Imperial lattops She was destroyed on 7 May 1942 in theBattle of the Coral Sea.Imperial lattopsAkagi,Kaga,Sōryū, andHiryū were lost in theBattle of Midway.^[16]

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.^[17][18] 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 againstNew Britain andNew Guinea in January 1942, First Kōkū Sentai and Fifth Kōkū Sentai participated.^[19]

The number (from approximately two dozen up to approximately 80 aircraft) and type of aircraft varied, based on the capacity of the aircraft carrier.^[20] The largefleet carriers had three types of aircraft;fighters,level/torpedo bombers, anddive 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 sixfleet carriers:Akagi,Kaga,Sōryū,Hiryū,Shōkaku, andZuikaku, and twolight carriers:Ryūjō andKasuga Maru (later renamedTaiyō), 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.^[21] On the same date, the Japanese Navy's front-line aircraft carriers and their aircraft units came under the command of the3rd Fleet, which was created in its sixth generation on that date.^[22]

TheKidō Butai (機動部隊, "Mobile Strike Force") was theCombined Fleet's tactical designation for its combinedcarrier battle groups.^[23] 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 theattack on Pearl Harbor under Vice-AdmiralChūichi Nagumo in 1941.^[24] For the attack, theKidō Butai consisted of six aircraft carriers (commanded by Chūichi Nagumo,Tamon Yamaguchi andChūichi Hara) with 414 airplanes, twobattleships, threecruisers, nine destroyers, eighttankers, 23submarines, and fourmidget submarines. However, these escort ships were borrowed from other fleets and squadrons. It was the single most powerful naval fleet until four of the six aircraft carriers of the unit were destroyed in the disastrousBattle of Midway.

Carriers of the Kidō Butai, 1941
1st Carrier Division
Akagi
Kaga
2nd Carrier Division
Sōryū
Hiryū
3rd Carrier Division
Zuihō
Hōshō
4th Carrier Division
Ryūjō
Taiyō
5th Carrier Division
Shōkaku
Zuikaku

Commander-in-Chief

No.	Portrait	Commander-in-Chief	Took office	Left office	Time in office
1		Nagumo, ChūichiVice Admiral Chūichi Nagumo 南雲 忠一 (1887–1944)	10 April 1941	14 July 1942	1 year, 95 days

Chief of Staff

No.	Portrait	Chief of Staff	Took office	Left office	Time in office
1		Kusaka, RyūnosukeRear Admiral Ryūnosuke Kusaka 草鹿 龍之介 (1893–1971)	10 April 1941	14 July 1942	1 year, 95 days

On 1 July 1943, the 1st Air Fleet was recreated^[25] as an exclusively land-based air fleet. It was intended to consist of nearly 1,600 aircraft when completed,^[26] but the war situation prevented it from reaching that figure, and the second generation of this fleet began with only two Kōkūtai: Dai 261 Kaigun Kōkūtai (a one-month-old Zerosen unit)^[27] and Dai 761 Kaigun Kōkūtai (a bomber unit that was created on the same day as this fleet was^[28]). On 30 September 1943, a cabinet meeting planned theAbsolute National Defense Zone (絶対国防圏,Zettai Kokubōken) strategy.^[29] The plan intended theKuril Islands,Bonin Islands,Mariana Islands,Caroline Islands,Biak,Sunda Islands andBurma to beunsinkable aircraft carriers. The 1st Air Fleet became the main force of this plan. However, it was soundly beaten in theBattle of the Philippine Sea. The IJN then moved the air fleet to thePhilippines to regroup. However, due partly to the aircrews' lack of combat experience, the air fleet suffered severe losses in theFormosa Air Battle. After the battle it had only 41 aircraft.^{[citation needed]} The only tactic left for them was thekamikaze attack.

Commanders-in-Chief

No.	Portrait	Commander-in-Chief	Took office	Left office	Time in office
1		Kakuta, KakujiVice Admiral Kakuji Kakuta 角田 覚治 (1890–1944)	1 July 1943	2 August 1944 †	1 year, 32 days
2		Teraoka, KinpeiVice Admiral Kinpei Teraoka [ja] 寺岡謹平 (1891–1984)	7 August 1944	20 October 1944	74 days
3		Ōnishi, TakijirōVice Admiral Takijirō Ōnishi 大西 瀧治郎 (1891–1945)	20 October 1944	10 May 1945	202 days
4		Shima, KiyohideVice Admiral Kiyohide Shima 志摩 清英 (1890–1973)	10 May 1945	15 June 1945	36 days

Chiefs of Staff

No.	Portrait	Chief of Staff	Took office	Left office	Time in office
1		Miwa, YoshitakeCaptain / Rear Admiral Yoshitake Miwa [ja] 三和義勇 (1899–1944)	1 July 1943	2 August 1944 †	1 year, 32 days
2		Odawara, ToshihikoCaptain Toshihiko Odawara [ja] 小田原俊彦 (1899–1945)	7 August 1944	1 January 1945	147 days
3		Kikuchi, TomozōRear Admiral Tomozō Kikuchi [ja] 菊池朝三 (1896–1988)	1 January 1945	10 May 1945	129 days
4		Nakazawa, TasukuRear Admiral Tasuku Nakazawa [ja] 中澤佑 (1894–1977)	10 May 1945	15 June 1945	36 days

• 
  AdmiralChūichi Nagumo (Commander-in-Chief, 1st Carrier Division)
• 
  Vice AdmiralTamon Yamaguchi (2nd Carrier Division)
• 
  Vice AdmiralKakuji Kakuta (4th Carrier Division - from 1941)
• 
  Vice AdmiralGunichi Mikawa (3rd Battleship Division)
• 
  Vice AdmiralSentarō Ōmori (1st Destroyer Squadron)
• 
  Vice AdmiralShigeyoshi Miwa (3rd Submarine Squadron)
• 
  Vice AdmiralRyūnosuke Kusaka (Chief of staff, 1st Air Fleet)
• 
  Rear AdmiralTomeo Kaku [ja] (2nd Carrier Division: Hiryu)
• 
  Rear AdmiralRyusaku Yanagimoto (2nd Carrier Division: Soryu)

TheKidō Butai (also known as theCarrier Striking Task Force) set sail fromHitokappu Bay, Japan underVice AdmiralChūichi Nagumo on 26 November 1941, arriving in Hawaiian waters on Sunday, 7 December 1941 Hawaiian time. At around 8am, the first wave began its attack on theUS Pacific Fleet based atPearl Harbor and on outlying airfields. By the end of the day, 21 Americanships were either sunk or crippled, 188 aircraft were destroyed, and almost 2,500 Americans were killed. Japan was now formally at war with the United States.

For theattack on Pearl Harbor, this fleet had a strength of 103level bombers, 128dive bombers, 40torpedo bombers, 88 fighter planes, plus 91 planes for a total of 441 planes.

The Bombing of Darwin on 19 February 1942 was the largest single attack ever mounted by a foreign power on Australia. On that day, 242 Japanese aircraft, in two separate raids, attacked the town, ships inDarwin's harbour and the town's two airfields in an attempt to prevent theAllies from using them as bases to contest theinvasion of Timor andJava. The town was only lightly defended and the Japanese inflicted heavy losses upon the Allied forces at little cost to themselves. The urban areas of Darwin also suffered some damage from the raids and there were a number of civilian casualties.

Between 31 March and 10 April 1942 the Japanese conducted a naval sortie against Allied naval forces in theIndian Ocean. The Fast Carrier Task Force (Kidō Butai), consisting of six carriers commanded by AdmiralChūichi Nagumo, inflicted heavy losses on the British fleet, with the sinking of 1 carrier, 2 cruisers, 2 destroyers, and 23 merchant ships for the loss of 20 aircraft.Attacks on the island ofCeylon were also carried out.

The 1st Air Fleet dispatched theFifth Carrier Division in theCoral Sea during the return from the Indian Ocean. On May 7 the USN sighted the Port Moresby invasion force and mistook it for the main carrier force. AdmiralFletcher sent an aircraft strike which sank the IJN light carrierShōhō. After this loss of air cover, the Port Moresby invasion force abandoned its mission and retreated north. On the same day the IJN sighted and sank USN destroyerSims andoilerNeosho. The primary action took place on 8 May. Both carrier forces sighted and attacked each other. As a result,Lexington was sunk andYorktown was damaged by a Japanese air strike. USN aircraft managed to damageShōkaku, meaning that she and her sister ship were unable to participate in the following operation. The remaining fleet returned to Japan to prepare for the Midway invasion (Operation MI).

AdmiralIsoroku Yamamoto planned to lure and destroy USN carriers by attacking the Midway Islands in June 1942. The Japanese were unaware that the United States had brokentheir naval code. As a result of this, USN carriers were already in the area when the Japanese attacked Midway. On 3 June US land-based bombers from Midway attacked the Japanese fleet but scored no hits. On 4 June, due to the poor reconnaissance efforts and tactical mistakes of Vice AdmiralChūichi Nagumo, USN dive bombers were able to surprise the Japanese carrier force and destroyed three carriers (Akagi,Kaga andSōryū). At the time of the attack the Japanese carriers were in the process of preparing to launch an air strike against the US carriers and their hangars were full of loaded aircraft, bombs and aviation fuel which decisively contributed to their destruction. CarrierHiryū managed to survive the attack and Rear AdmiralTamon Yamaguchi launched a strike againstYorktown. Aircraft fromHiryū managed to crippleYorktown, which was later sunk byJapanese submarine I-168. In response, the US launched a strike againstHiryū and sank her. That day the Japanese lost four aircraft carriers and much of their experienced aircrew.

The US Navy's attack on the Japanese base atTruk (Chuuk) on 17 February 1944 (Operation Hailstone) surprised the Japanese military. In response, the Japanese Navy ordered all of the 61st Air Flotilla to theMariana Islands.^[30] Its Number 261 Kaigun Kōkūtai (fighter) advanced to Saipan circa 19–24 February 1944, but attrition in air combats and illness weakened the unit greatly and it played only a minor role in the Battle of the Philippine Sea.^[31] Elements of No. 263 Kaigun Kōkūtai (fighter) of the 61st Air Flotilla were stationed on Guam from 15 June 1944 and participated in the battle.^[32]

After disastrous losses at theBattle of the Philippine Sea, the Japanese carrier force was again practically without aircrew and aircraft. This meant that at theBattle of Leyte Gulf the IJN carrier force was only used as a decoy force where it was ultimately destroyed, the battle that saw the lastKidō Butai survivor,Zuikaku, along withZuiho,Chiyoda andChitose succumbing to US air attacks of AdmiralWilliam F. Halsey'sTask Force 38.

• Hata, Ikuhiko; Izawa, Yasuho and Shores, Christopher, (2011).Japanese Naval Air Force Fighter Units and Their Aces 1932–1945, Grub Street,ISBN 978-1-906502-84-3
• Parshall, Jonathan; Tully, Anthony (2005).Shattered Sword: The Untold Story of the Battle of Midway. Dulles, Virginia: Potomac Books.ISBN 1-57488-923-0.
• 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.,ISBN 0-14-00-6455-9
• Thorpe, Donald W. (1977).Japanese Naval Air Force Camouflage and Markings World War II. Fallbrook, CA: Aero Publishers, 1977.ISBN 0-8168-6583-3 (hardcover; paperbackISBN 0-8168-6587-6).
• "Monthly the Maru" series, and "The Maru Special" series,"Ushio Shobō".Archived from the original on 6 June 2009. (Japan)
• "Monthly Ships of the World" series,"Kaijinsha".Archived from the original on 31 May 2009. (Japan)
• "Famous Airplanes of the World" series and "Monthly Kōku Fan" series, Bunrindō (Japan)

• Kidō Butai at Combined Fleet.com

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