Nagumo led Japan's main carrier battle group, the Kido Butai, in the attack on Pearl Harbor in 1941, and over the next months in successful raids on Darwin in Australia and in the Indian Ocean.

From 1925 to 1926, Nagumo accompanied a Japanese mission to study naval warfare strategy, tactics, and equipment in Western Europe and the United States.

As a Rear Admiral, Nagumo commanded the 8th Cruiser Division to support Imperial Japanese Army movements in China from the Yellow Sea.

On 10 April 1941, Nagumo was appointed commander-in-chief of the First Air Fleet, the IJN's main carrier battle group, largely due to his seniority.

[5] Mentally, he had become a cautious officer who carefully worked over the tactical plans of every operation in which he was involved; his inflexibility in command decisions became more apparent.

[5] Despite his limited experience, he was a strong advocate of combining sea and air power, although he was opposed to Admiral Yamamoto's plan to attack the United States Navy Naval Station Pearl Harbor.

The aircraft, either attempting a suicide ramming, or out of control, narrowly missed striking the carrier's bridge, which could have killed Nagumo, before it crashed into the ocean.

[11][12] Nagumo soon launched another attack on Midway, in direct violation of Yamamoto's order to keep the reserve strike force armed for anti-ship operations.

[13] That change in plans required arming the available planes with bombs, suitable for attacking land targets, rather than torpedoes, designed for anti-ship actions.

American dive-bombers attacked Akagi, Kaga and Sōryū, resulting in fires and further explosions due to unsecured ordinance, crippling all three.

[19] Afterwards, Nagumo was reassigned as commander-in-chief of the Third Fleet and commanded aircraft carriers in the Guadalcanal campaign in the battles of the Eastern Solomons and the Santa Cruz Islands.

His actions were largely indecisive, and with Japanese naval forces steadily losing manpower, fuel, and material for building replacement ships and aircraft, the fleet gradually frittered away most of its strength.

From October 1943 to February 1944, Nagumo was once again made commander-in-chief of First Fleet, which was by that time largely involved in only training duties to conserve what little remained of Japan's air force.

On 6 July 1944, Nagumo, unable to defend his position any longer and refusing to be taken captive, killed himself with a pistol shot to his temple.