First London Naval Treaty

The Treaty for the Limitation and Reduction of Naval Armament, commonly known as the London Naval Treaty, was an agreement between the United Kingdom, the Empire of Japan, France, Italy and the United States, signed on 22 April 1930, which regulated submarine warfare and limited naval shipbuilding. Ratifications were exchanged in London on 27 October 1930, and the treaty went into effect on the same day. It was registered in League of Nations Treaty Series on 6 February 1931.

The signing of the treaty remains inextricably intertwined with the ongoing negotiations which began before the official start of the London Naval Conference of 1930, evolved throughout the progress of the official conference schedule, and continued for years thereafter.

The terms of the treaty were seen as an extension of the conditions agreed in the Washington Naval Treaty, an effort to prevent a naval arms race after World War I.

The Conference was a revival of the efforts which had gone into the Geneva Naval Conference of 1927. At Geneva, the various negotiators had been unable to reach agreement because of bad feeling between the British Government and that of the United States. The problem may have initially arisen from discussions held between President Herbert Hoover and Prime Minister Ramsay MacDonald at Rapidan Camp in 1929, but a range of factors affected tensions, exacerbated by the other nations at the conference.

Under the treaty, the standard displacement of submarines was restricted to 2,000 tons, with each major power being allowed to keep three submarines of up to 2,800 tons and France one. Submarine gun caliber was also restricted for the first time to 6.1 in (155 mm) with one exception, an already-constructed French submarine allowed to retain 8 in (203 mm) guns. That put an end to the 'big-gun' submarine concept pioneered by the British M class and the French Surcouf.

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