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The Washington Naval Treaty, also known as the Five-Power Treaty, limited the naval armaments of its five signatories: the United States, the British Empire, the Empire of Japan, France, and Italy. The treaty was agreed at the Washington Naval Conference, which was held in Washington, D.C. from November 1921 to February 1922.
The treaty limited the total capital ship tonnage of each of the signatories; no single ship could exceed 35,000 tons, and no ship could carry a gun in excess of 16 inches. Only two large aircraft carriers were permitted per nation. No new fortifications or naval bases could be established, and existing bases and defenses could not be improved in the external territories and possessions specified in the treaty. The tonnage allotment to Japan was based on a 5:5:3 ratio compared with the United States and United Kingdom, with the justification being that the latter countries needed to maintain fleets on more than one ocean, whereas Japan had only the Pacific Ocean.
The terms of the treaty were extremely unpopular with the Japanese public, many of whom saw the 5:5:3 ratio as another way of being regarded as an inferior race by the West.
The Imperial Japanese Navy was also split into two opposing factions, Fleet Faction and Treaty Faction. The Treaty Faction argued that Japan could not afford an arms race with the western powers, and hoped through diplomacy to restore the Anglo-Japanese Alliance. It argued that the current treaty limitations would serve Japan for the time being.
The Treaty Faction was composed of the political left-wing within the Navy, including influential admirals in the Navy Ministry such as Takarabe Takeshi, Taniguchi Naomi, Yamanashi Katsunoshin, Sakonji Seizo and Hori Taikichi.
In the 1920s, the Treaty Faction, which was supported by the civilian government, was predominant. However, the even more restrictive London Naval Treaty of 1930 divided the Treaty Faction into two parts. The “Anti-London Treaty Faction” pushed for military and economic expansion into the South Pacific, and thus became more closely aligned with the "Fleet Faction".
With increasing Japanese militarism in the 1930s, the growing conflict with the United States over China, and the blatant disregard for the terms of the Treaty by all major powers, the Fleet Faction gradually gained the upper hand. Furthermore, many of the Treaty Faction members who had direct first-hand experience in Britain or the United States went into retirement from 1933-1934, including Isoroku Yamamoto's mentor, Hori Teikichi.
On 29 December 1934, the Japanese government gave formal notice that it intended to terminate the treaty. Its provisions remained in force until the end of 1936, and it was not renewed.