Treaty for the Limitation of Naval Armament

The Limitation of Naval Armament included many separate treaties. In general, the treaties involved the United States, United Kingdom, Japan, Italy and France.

One of the treaties, known as the Four Power Act, provided that the US, UK, Japan and France would help maintain peace in the Pacific Ocean, while another, the Five Power Treaty, stipulated that the US, UK and Japan would build ships in a 5:5:3 ratio. This was originally proposed by US Secretary of State Charles Evans Hughes, and was rejected by the Japanese. Tokyo agreed, however, when a provision was added forbidding the US and UK to fortify their Pacific island possessions, but allowing Japan to do so. A third treaty, the Nine Power Treaty, emphasized maintaining an Open Door Policy in China.

The treaties came into effect as the result of the Washington Disarmament Conference, held by the US in 1921–22.

The world's popular mood was peace and disarmament throughout the 1920s. At the end of the Great War, Britain still had the largest navy afloat but its big ships were becoming obsolete, and the Americans and Japanese were rapidly building expensive new warships. London and Tokyo were allies in a treaty that was due to expire in 1922. Although there were no immediate dangers, observers increasingly pointed to the American-Japanese rivalry for control of the Pacific Ocean as a long-term threat to world peace. By this time, London realized it had best cast its lot with Washington rather than Tokyo. To stop a needless, expensive and possibly dangerous arms race, the major countries signed a series of naval disarmament agreements. The most important was the Washington Conference of 1922, sponsored by President Warren Harding and run by Secretary of State Charles Evans Hughes. Harding demanded action in order to gain domestic political credit. Hughes, helped by the cryptographers who were reading the Japanese diplomatic secrets, brilliantly engineered a deal that everyone though best for themselves. To resolve technical disputes about the quality of warships, the conferees adopted a quantitative standard, based on tonnage displacement (a simple measure of the size of a ship). A ten-year agreement fixed the ratio of battleships at 5:5:3—that is 525,000 tons for the USA, 525,000 tons for Britain, and 315,000 tons for Japan. The dominant weapons systems of the era—battleships—could be no larger than 35,000 tons. The major powers allowed themselves 135,000:135,000:81,000 tons for the newfangled aircraft carriers. The Washington Conference exactly captured the worldwide popular demand for peace and disarmament; without it, the US, Britain and Japan would have engaged in an expensive buildup, with each worried the other two might be getting too powerful. The agreements forced the US to scrap 15 old battleships and two new ones, along with 13 ships under construction. Britain had to scrap ships too—indeed, more warships were lost at Washington than at any battle in history.