Japanese aircraft carrier Akagi participant of Indian Ocean raid
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 Amagi-class battlecruiser, 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.
Akagi's 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's 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 Enterprise, Hornet, and Yorktown. Dive bombers 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.Indian Ocean raid
On 26 March, Akagi set sail for the Indian Ocean raid with the rest of the Kido Butai. The Japanese intent was to defeat the British Eastern Fleet and destroy British airpower in the region in order to secure the flank of their operations in Burma. On 5 April 1942, Akagi launched 17 B5Ns and 9 Zeros in an air strike against Colombo, Ceylon, which damaged the port facilities. None of the aircraft were lost and the Zero pilots claimed to have shot down a dozen of the defending British fighters. Later that day, 17 D3As from Akagi helped to sink the British heavy cruisers Cornwall and Dorsetshire. On 9 April, she attacked Trincomalee with 18 B5Ns, escorted by 6 Zeros which claimed to have shot down 5 Hawker Hurricane fighters (only two of which can be confirmed from Allied records) without loss to themselves. Meanwhile, a floatplane from the battleship Haruna spotted the small aircraft carrier Hermes, escorted by the Australian destroyer Vampire, and every available D3A was launched to attack the ships. Akagi contributed 17 dive bombers and they helped to sink both ships; they also spotted the oil tanker RFA Athelstone, escorted by the corvette Hollyhock, and sank both without loss. During the day's actions, the carrier narrowly escaped damage when nine British Bristol Blenheim bombers from Ceylon penetrated the CAP and dropped their bombs from 11,000 feet (3,400 m), just missing the carrier and the heavy cruiser Tone. Four of the Blenheims were subsequently shot down by CAP fighters and one was shot down by aircraft from the carriers' returning air strike. After the raid, the carrier mobile striking force returned to Japan to refit and replenish.On 19 April 1942, while near Taiwan during the transit to Japan, Akagi, Sōryū, and Hiryū were sent in pursuit of the American carriers Hornet and Enterprise, which had launched the Doolittle Raid. They found only empty ocean, however, for the American carriers had immediately departed the area to return to Hawaii. Akagi and the other carriers shortly abandoned the chase and dropped anchor at Hashirajima anchorage on 22 April. On 25 April, Captain Taijiro Aoki relieved Hasegawa as skipper of the carrier.  Having been engaged in constant operations for four and a half months, the ship, along with the other three carriers of the First and Second Carrier Divisions, was hurriedly refitted and replenished in preparation for the Combined Fleet's next major operation, scheduled to begin one month hence. The Fifth Carrier Division, with Shōkaku and Zuikaku, had been detached in mid-April to support Operation Mo, resulting in the Battle of the Coral Sea. While at Hashirajima, Akagi's air group was based ashore in Kagoshima and conducted flight and weapons training with the other First Air Fleet carrier units.