Originally intended to be one of two Tosa-class battleships, Kaga was converted under the terms of the Washington Naval Treaty to an aircraft carrier as the replacement for the battlecruiser Amagi, which had been irreparably damaged during the 1923 Great Kantō earthquake.

Kaga was rebuilt in 1933–1935, increasing her top speed, improving her exhaust systems, and adapting her flight decks to accommodate more modern, heavier aircraft.

The following month her aircraft participated in a combined carrier airstrike on Darwin, Australia, and helping secure the conquest of the Dutch East Indies by Japanese forces.

Dive bombers from Enterprise severely damaged Kaga; when it became obvious she could not be saved, she was scuttled by Japanese destroyers to prevent her from falling into enemy hands.

The formal decision to convert Kaga to an aircraft carrier was issued 13 December 1923, but no work took place until 1925 as new plans were drafted and earthquake damage to the Yokosuka Naval Arsenal was repaired.

[14] 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 other features made her more of a target in any surface action than a fighting warship.

[19] The First Carrier Division, along with Hōshō, departed for Chinese waters on 29 January 1932 to support Imperial Japanese Army troops during the Shanghai Incident as part of the IJN's 3rd Fleet.

[21] Kaga's aircraft, operating from both the carrier and a temporary base at Kunda Airfield in Shanghai, flew missions in support of Japanese ground forces throughout February 1932.

Kaga and the other carriers were initially given roles as tactical force multipliers supporting the fleet's battleships in the IJN's "decisive battle" doctrine.

Aerial strikes against enemy carriers were later, beginning around 1932–1933, deemed of equal importance in order to establish air superiority during the initial stages of battle.

[23] Kaga was soon judged inferior to Akagi because of her slower speed, smaller flight deck (64 feet (19.5 m) shorter), and problematic funnel arrangement.

Kaga was equipped with eight improved oil-burning models of the Kampon Type B (Ro) with a working pressure of 22 kg/cm2 (2,157 kPa; 313 psi) at a temperature of 300 °C (572 °F).

The space freed up by the removal of the funnel ducts was divided into two decks and converted into living quarters for the expanded air group.

[32][33] Kaga aircraft fought their first battle on 15 August 1937, when thirteen Aichi D1A1 (Type 94) dive-bombers encountered Chinese Air Force Curtiss A-12 Shrike attack-bombers of the 26th and 27th Squadrons at Chao'er Airbase preparing for strikes against Japanese positions in Shanghai, and a dogfight duly ensued between the two unlikely dogfighting opponents; two D1A1s were shot down; a third badly shot-up D1A1 returned to Kaga with a fatally wounded crewman, while the D1A1 flight claimed three Shrikes.

Using Taiwan (then part of the Empire of Japan) as its base, the carrier steamed 29,048 nautical miles (53,797 km; 33,428 mi) supporting military operations from the South and East China Seas.

During that time, Kaga bombers supported army operations by attacking enemy railroad bridges, airfields, and transportation vehicles.

[41] Kaga's fighter group at this time included future aces Jirō Chōno, Osamu Kudō, Yoshio Fukui, Watari Handa, Masaichi Kondō, Hatsuo Hidaka, Kiichi Oda, Satoru Ono, and Chitoshi Isozaki.

[42] The US Navy decrypted an IJN message which reportedly indicated that the attack on the Panay and other neutral ships in the Yangtze River had been knowingly and deliberately planned by an air officer on Kaga.

The IJN's fleet CAP consisted of too few fighter aircraft and was hampered by an inadequate early warning system, including a lack of radar.

During the morning of 7 December 1941 Kaga aircraft participated in both First Air Fleet strikes launched against Oahu from a position 230 nautical miles (430 km) north of the island.

[50] Kaga's bomber and torpedo crews claimed hits on the battleships Nevada, Oklahoma, Arizona, California, West Virginia, and Maryland.

This process normally took about an hour and a half; more time would be required to bring the aircraft up to the flight deck and warm up and launch the strike group.

[59] Kaga's four remaining CAP fighters were in the process of landing when 16 Marine SBD Dauntless dive-bombers from Midway, led by Lofton R. Henderson, attacked Hiryū around 07:55 without result.

[60] Five Zeros were launched at 08:15 and three intercepted a dozen Midway-based United States Army B-17 Flying Fortresses attempting to bomb the three other carriers from 20,000 feet (6,100 m), but only limited damage was inflicted on the heavy bombers, although their attacks all missed.

Kaga began landing her returning Midway strike force aboard around 08:35 and was finished by 08:50; one Zero pilot died after crash-landing his aircraft.

[66] Warrant Officer Takeshi Maeda, an injured Kaga B5N aircrew member rescued by Hagikaze, described the scene: "My comrade carried me up to the deck so I could see the last moments of our beloved carrier, which was nearby.

[68][Note 13] Kaga's surviving crewmembers were restricted incommunicado to an airbase in Kyūshū for one to two months after returning to Japan, to help conceal word of the Midway defeat from the Japanese public.

[72] They employed the research vessel Melville during a survey of a fleet exercise area with the US Navy's recently modified SEAMAP acoustic imaging system.

[73] The wreckage included a 50-foot (15 m) long section of hangar bulkhead, two 25 mm anti-aircraft gun tubs, and a landing light array.

Rob Kraft, David W. Jourdan and Naval History and Heritage Command historian Frank Thompson aboard RV Petrel.