IJN aircraft carrier Akagi, c. 1930
Kaga was laid down on 19 July 1920 in the Kawasaki shipyard in Kobe and the completed hull was launched on 17 November 1921.
Originally intended to be one of two Tosa-class battleships, Kaga was converted, under the terms of the then-recently concluded Washington Naval Treaty, into an aircraft carrier (as the replacement for the battlecruiser Amagi, which had been damaged during the 1923 Great Kantō earthquake). Kaga was rebuilt in 1933–35, increasing her top speed, improving her exhaust systems, and adapting her flight decks to more modern, heavier aircraft.
The now-converted aircraft carrier Kaga first supported Japanese troops in China during the Shanghai Incident of 1932 and participated in the Second Sino-Japanese War in the late 1930s. With five other fleet carriers, Kaga took part in the Pearl Harbor raid in December 1941 and the invasion of Rabaul in the Southwest Pacific in January 1942. The following month, her aircraft participated in a combined carrier airstrike on Darwin, Australia, helping to secure the conquest of the Dutch East Indies by Japanese forces.
At the Battle of Midway, the Imperial Japanese Navy was surprised by the appearance of three American carriers and, partly due to Admiral Isoroku Yamamoto’s defensive plan – in which ships were too dispersed to support each other – Kaga, along with the other three IJN carriers, was sunk by aircraft from USS Enterprise, Hornet and Yorktown on 4 June.