Akagi (Japanese: 赤城, "red castle") was an aircraft carrier built for the Imperial Japanese Navy (IJN), named after Mount Akagi in present-day Gunma Prefecture. 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 Kaga 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 October 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 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. ¥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. 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. The rest of her guns were placed in reserve and scrapped in 1943.
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).
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.