was an aircraft carrier built for the Imperial Japanese Navy (IJN). Though she was laid down as an , Akagi was converted to an aircraft carrier while still under construction to comply with the terms of the Washington Naval Treaty. The ship was rebuilt from 1935 to 1938 with her original three flight decks consolidated into a single enlarged flight deck and an island superstructure. The second Japanese aircraft carrier to enter service, and the first large or "fleet" carrier, Akagi and the related figured prominently in the development of the IJN's new carrier striking force doctrine that grouped carriers together, concentrating their air power. This doctrine enabled Japan to attain its strategic goals during the early stages of the Pacific War from December 1941 until mid-1942.
Akagis aircraft served in the Second Sino-Japanese War in the late 1930s. Upon the formation of the First Air Fleet or Kido Butai (Striking Force) in early 1941, she became its flagship, and remained so for the duration of her service. With other fleet carriers, she took part in the Attack on Pearl Harbor in December 1941 and the invasion of Rabaul in the Southwest Pacific in January 1942. The following month, her aircraft bombed Darwin, Australia, and assisted in the conquest of the Dutch East Indies. In March and April 1942, Akagi aircraft helped sink a British heavy cruiser and an Australian destroyer in the Indian Ocean Raid.
After a brief refit, Akagi and three other fleet carriers of the Kido Butai participated in the Battle of Midway in June 1942. After bombarding American forces on the atoll, Akagi and the other carriers were attacked by aircraft from Midway and the carriers , , and . A single dive bomber from Enterprise severely damaged Akagi. When it became obvious she could not be saved, she was scuttled by Japanese destroyers to prevent her from falling into enemy hands. The loss of Akagi and three other IJN carriers at Midway was a crucial strategic defeat for Japan and contributed significantly to the Allies' ultimate victory in the Pacific. Her wreck was located in 2019 by the research vessel Petrel.
Design Construction and launch
Akagi was laid down as an at Kure, Japan, on 6 December 1920. Construction was halted, however, when Japan signed the Washington Naval Treaty on 6 February 1922. The treaty placed restrictions on the construction of battleships and battlecruisers although it authorized the conversion of two battleship or battlecruiser hulls under construction into aircraft carriers of up to displacement. The IJN had decided, following the launch of its first aircraft carrier, , to construct two larger, faster carriers for operations with major fleet units. The incomplete hulls of and Akagi were thus selected for completion as the two large carriers under the 1924 fleet construction program.Lengerer, p. 128Peattie, p. 54; Watts, p. 171; Jentschura, Jung and Mickel, p. 36; Parshall and Tully, pp. 6–7 ¥24.7 million was originally budgeted to complete Akagi as a battlecruiser and an estimated ¥8 million had been expended when construction stopped in February 1922. Shortly thereafter, the Diet approved an additional ¥90 million to complete Akagi and Amagi as carriers.Parshall and Tully, pp. 7, 535 Her guns were turned over to the Imperial Japanese Army for use as coastal artillery; one of her main-gun turrets was installed on Iki Island in the Strait of Tsushima in 1932.Gibbs, p. 217 The rest of her guns were placed in reserve and scrapped in 1943.Gibbs & Tamura, pp. 192, 194
Construction of Akagi as an aircraft carrier began on 19 November 1923. Amagis hull was damaged beyond economically feasible repair in the Great Kantō earthquake of 1 September 1923 and was broken up and scrapped. Akagi, the only remaining member of her class, was launched as a carrier on 22 April 1925 and commissioned at Kure Naval Arsenal on 25 March 1927, although trials continued through November 1927. She was the second carrier to enter service with the IJN, after Hōshō and before (which replaced Amagi).Watts, p. 65; Jentschura, Jung and Mickel, p. 36
Since Akagi was initially conceived as a battlecruiser, the prevailing ship naming conventions dictated that she (like her sister ships) be named after a mountain. Akagi came from Mount Akagi, a dormant volcano in the Kantō region (the name literally means "red castle"). After she was redesignated as an aircraft carrier, her mountain name remained, in contrast to ships like that were originally built as aircraft carriers, which were named after flying creatures. Her name was previously given to the Maya-class gunboat Akagi.Goldstein, Dillon and Wenger, p. 8
Akagi was completed at a length of overall. She had a beam of and, at deep load, a draft of . She displaced at (standard) load, and at full load, nearly less than her designed displacement as a battlecruiser.Lengerer, p. 129 Her complement totaled 1,600 crewmembers.Parshall and Tully, p. 463
Flight deck arrangements Akagi and Kaga were completed with three superimposed flight decks, the only carriers ever to be designed so. The British carriers converted from "large light cruisers", , , and , each had two flight decks, but there is no evidence that the Japanese copied the British model. It is more likely that it was a case of convergent evolution to improve launch and recovery cycle flexibility by allowing simultaneous launch and recovery of aircraft.Brown, p. 2 Akagis main flight deck was long and wide,Peattie, p. 229 her middle flight deck (beginning right in front of the bridge) was only long and her lower flight deck was long. The utility of her middle flight deck was questionable as it was so short that only some lightly loaded aircraft could use it, even in an era when the aircraft were much lighter and smaller than during World War II.Lengerer, p. 130 The upper flight deck sloped slightly from amidships toward the bow and toward the stern to assist landings and takeoffs for the underpowered aircraft of that time.Peattie, p. 54
As completed, the ship had two main hangar decks and a third auxiliary hangar, giving a total capacity of 60 aircraft. The third and lowest hangar deck was used only for storing disassembled aircraft. The two main hangars opened onto the middle and lower flight decks to allow aircraft to take off directly from the hangars while landing operations were in progress on the main flight deck above. The upper and middle hangar areas totaled about , the lower hangar about . No catapults were fitted. Her forward aircraft lift was offset to starboard and in size. Her aft lift was on the centerline and . The aft elevator serviced the upper flight deck and all three hangar decks. Her arresting gear was an unsatisfactory British longitudinal system used on the carrier Furious that relied on friction between the arrester hook and the cables. The Japanese were well aware of this system's flaws, as it was already in use on their first carrier, Hōshō, but had no alternatives available when Akagi was completed. It was replaced during the ship's refit in 1931 with a Japanese-designed transverse cable system with six wires and that was replaced in turn before Akagi began her modernization in 1935 by the Kure Model 4 type (Kure shiki 4 gata). There was no island superstructure when the carrier was completed; the carrier was commanded from a space below the forward end of the upper flight deck.Peattie, pp. 54–55; Parshall and Tully, pp. 462–463 The ship carried approximately of aviation fuel for her embarked aircraft.Parshall and Tully, p. 477
As originally completed, Akagi carried an air group of 28 Mitsubishi B1M3 torpedo bombers, 16 Nakajima A1N fighters and 16 Mitsubishi 2MR reconnaissance aircraft.
Armament and armor
Akagi was armed with ten 50-caliber 20 cm 3rd Year Type No. 1 guns, six in casemates aft and the rest in two twin-gun turrets, one on each side of the middle flight deck. They fired projectiles at a rate of 3–6 rounds per minute with a muzzle velocity of at 25°, this provided a maximum range between . The turrets were nominally capable of 70° elevation to provide additional anti-aircraft fire, but in practice the maximum elevation was only 55°. The slow rate of fire and the fixed 5° loading angle minimized any real anti-aircraft capability.Campbell, pp. 185–188 This heavy gun armament was provided in case she was surprised by enemy cruisers and forced to give battle, but her large and vulnerable flight deck, hangars, and superstructure made her more of a target in any surface action than a fighting warship. Carrier doctrine was still evolving at this time and the impracticality of carriers engaging in gun duels had not yet been realized.Peattie, pp. 53, 55
The ship carried dedicated anti-aircraft armament of six twin 45-caliber 12 cm 10th Year Type gun mounts fitted on sponsons below the level of the funnels, where they could not fire across the flight deck, three mounts per side.Lengerer, p. 131 These guns fired projectiles at a muzzle velocity of ; at 45°, this provided a maximum range of , and they had a maximum ceiling of at 75° elevation. Their effective rate of fire was 6–8 rounds per minute.Campbell, p. 194
Akagis waterline armored belt was reduced from and placed lower on the ship than originally designed. The upper part of her torpedo bulge was given of armor. Her deck armor was also reduced from .Lengerer, pp. 128, 130 The modifications improved the ship's stability by helping compensate for the increased topside weight of the double hangar deck.
Propulsion In Akagi predecessor, Hōshō, the hot exhaust gases vented by swivelling funnels posed a danger to the ship, and wind-tunnel testing had not suggested any solutions. Akagi and Kaga were given different solutions to evaluate in real-world conditions. Akagi was given two funnels on the starboard side. The larger, forward funnel was angled 30° below horizontal with its mouth facing the sea, and the smaller one exhausted vertically a little past the edge of the flight deck. The forward funnel was fitted with a water-cooling system to reduce the turbulence caused by hot exhaust gases and a cover that could be raised to allow the exhaust gases to escape if the ship developed a severe list and the mouth of the funnel touched the sea. Kaga adopted a version of this configuration when she was modernized during the mid-1930s.Lengerer, pp. 130–131, 137; Peattie, p. 54
Akagi was completed with four Gihon geared steam turbine sets, each driving one propeller shaft, that produced a total of . Steam for these turbines was provided by nineteen Type B Kampon boilers with a working pressure of . Some boilers were oil-fired, and the others used a mix of fuel oil and coal. As a battlecruiser, she was expected to achieve , but the reduction in displacement from increased her maximum speed to , which was reached during her sea trials on 17 June 1927. She carried of fuel oil and of coal that gave her a range of at .Lengerer, pp. 129, 131
Early service
Akagi joined the Combined Fleet in August 1927 and was assigned to the First Carrier Division upon its formation on 1 April 1928, serving as the division's flagship under Rear Admiral Sankichi Takahashi. The carrier's early career was uneventful, consisting of various training exercises. From 10 December 1928 to 1 November 1929, the ship was captained by Isoroku Yamamoto, future commander of the Combined Fleet.Tully; Peattie, pp. 72, 323; Hata and Izawa, p. 20; Lengerer, pp. 130, 170–171; Hoyt, pp. 60–63.