In this capacity, he served as the navy's commander-in-chief in the Asia-Pacific theater of World War II until his removal in February 1944.

The closest he came to combat was commanding a land-based heavy naval gun unit during the siege of Port Arthur.

From January 1913 to April 1915, he was a language officer in the United States, during which time he studied at Harvard Law School.

Nagano introduced and influenced Progressive education method such as Dalton Plan to Japanese Naval Academy.

[citation needed] Japan withdrew in protest from the 1935 London Conference after it was denied naval parity with the United States and Great Britain.

A staunch believer in Nanshin-ron , Admiral Nagano played a central role in Japan's decision to go to war with the United States.

[5] At the end of the month, Nagano informed Emperor Hirohito that the nation's oil supply would run out in two years if the embargo was not lifted.

[7] By September 1941, he and the Army's Chief of Staff, General Hajime Sugiyama, called for Japan to be placed on an immediate war-footing and for an end to all negotiations by mid-October.

[8] According to some Japanese sources, Nagano presented a peace proposal before a conference on November 1, 1941 but this was ultimately struck down by Prime Minister Tojo Hideki.

Viewing it as a needless diversion of Japan's carrier fleet, Nagano initially opposed Admiral Isoroku Yamamoto's planned attack on Pearl Harbor.

"[16] He died of a heart attack due to complications arising from pneumonia in Sugamo Prison in Tokyo before the conclusion of his trial.