Imperial Japanese Navy

From its beginning during the Meiji Restoration in 1869, to its World War II defeat in 1945, the Imperial Japanese Navy (Nihon Kaigun) was the branch of the Japanese military responsible for naval warfare. When the postwar Constitution renounced war, naval functions moved to the Japanese Maritime Self-Defense Agency.

Policy

Both the Army and Navy took an active part in driving foreign policy, with the only check on them being the attitudes of Emperor Hirohito. The Navy opposed the 1930 London Naval Treaty, but Hirohito had his chief aide, Tajeki Nara pressure Fleet Admiral Togo into agreeing to the treaty, and his Grand Chamberlain, Kantaro Suzuki, pressure the Naval General Staff.

The Cabinet Law (Japan) gave the Army and Navy a de facto veto over any Japanese government, since it required that the Army and Navy present candidate Army and Navy Minister from the list of serving officers. If a service declined to name a candidate, no Prime Minister could form a government.

Operations

While competition between armies and navies was common in many nations, there was unusual separation, despite the existence of Imperial General Headquarters (Japan), between the Japanese Army and Navy. Again as with other countries, there was a Navy Ministry with administrative responsibility and a Naval General Staff headed by the senior professional Chief of Naval General Staff. Below the Chief of Staff was the Commander-in-Chief, Combined Fleet, who had operational but not policy responsibility. For example, Admiral Isoroku Yamamoto had been Navy Vice-Minister during the policy discussions about starting the Second World War. He was transferred to Combined Fleet, in part, because there was a credible assassination threat to him from pro-war zealots, and, since the CinC's headquarters was on a battleship, he could be better protected.

Doctrine

Japanese doctrine emphasized great, decisive surface battles in the model of Alfred Thayer Mahan. While they started WWII with extremely competent naval aviation, much of the leadership still believed the battleship supreme. A critical error was that the Navy did not institute a pilot rotation system, so there was no supply of rested veterans and new pilots they had taught.

Mid-level organization

Numbered Japanese fleets generally corresponded to what the U.S. called type commands. Second Fleet, for example, was the technical headquarters for battleships, corresponding to U.S. Commander, Battleships, Pacific Fleet. First Fleet had carriers and Sixth Fleet had submarines, although some fleets were regional. The actual operational organizations were usually "Forces", such as the carrier-centric Mobile Force. Within the fleets, as in American practice, were divisions and squadrons of the same type of ship, which were then assigned to forces.

Forces could contain subordinate units called forces; Japan did not use hierarchies such as the U.S. task force/task group/task unit.