The outcome of the Washington Naval Disarmament Treaty left the Imperial Japanese Navy with several incomplete capital ships destined for the scrapyard, As the Americans and British had declared their intention of converting similar hulls into carriers, and in the light of successful experience with the Hosho, the naval staff decided to press ahead with two similar carrier conversions Two battle-cruisers, to be known as Akagi and Amagi, were chosen; these were projected as 40,000-ton ships capable of 30 knots. Work started in 1923 but the hull of the Amagi was badly damaged during the great Tokyo earthquake in September,and she was scrapped.
The Akagi was completed in March 1927, a flush-decked ship with two funnels at the starboard edge of the flight deck, a triple flight deck forward, and 10 200-mm (7.9-in) guns, six of them in old-fashioned casemates low down aft. Ten years later she was completely rebuilt, with a small island superstructure on the port side, and a full-length flight deck. It was hoped that the portside island would simplify operations when operating in company with other carriers (allowing her aircraft to be marshalled separately) but it caused far more landing accidents than a starboard island.
With her half-sister Kaga she formed Carrier Division 1 and as Vice Admiral Nagumo's flagship led the attack on Pearl Harbor. She then led the other carriers on a brilliant series of raids through the East Indies and Indian Ocean, the force sinking the British carrier Hermes, driving the Allies out of Java and Sumatra and even getting as far as Darwin in northern Australia. At the Battle of Midway on 4 June 1942 Akagi's air group attacked Midway itself, and she suffered slight damage when a shore-based torpedobomber bounced off the deck early in the morning. At 10.22 she was attacked by aircraft from the USS Enterprise, which hit her twice with bombs. A 1,000-lb (454-kg) bomb burst in the hangar and started a fire among torpedo-warheads which spread to aviation fuel spilling from fractured lines; a second bomb (of 500 lb/227 kg) also started a fire among aircraft parked on the flight deck, Within 30 minutes the fire was out of control and Nagumo had shifted his flag to a light cruiser. The Akagi was abandoned but burned for another 9 hours or more. After vain efforts to board her the order was given to a destroyer to torpedo her.
Displacement: (1941) 36,500 tons standard, 42,000 tons full load
Dimensions: length 260,6 m (855 ft 0 in) overall; beam 31.3 m (102 ft 8 in); draught 8.6 m (28 ft 3 in)
Machinery: 4-shaft geared steam turbines delivering 133,000 shp (99180kW)
Speed: 31 knots
Armament: six 200-mm (7.9-in), six twin 120-mm (4.7-in) AA, and 14 twin 25-mm AAguns
Aircraft: (June 1942) 21 Mitsubishi A6M Zero fighters, 21 Aichi D3A Val divebombers and 21 Nakajima B5N 'Kate' torpedo-bombers
Complement: 1,340 officers and men