Disarmament: Washington Naval Treaty

USS Montana (BB-51) under construction at Mare Island Navy Yard. Photograph Courtesy of the US Naval History & Heritage Command

The Washington Naval Conference

Following the end of World War I, the United States, Great Britain, and Japan all commenced large-scale programs of capital ship construction. In the United States, this took the form of five new battleships and four battlecruisers, while across the Atlantic the Royal Navy was preparing to build its series of G3 Battlecruisers and N3 Battleships. For the Japanese, the postwar naval construction began with a program calling for eight new battleships and eight new battlecruisers. This building spree led to concern that a new naval arms race, similar to the pre-war Anglo-German competition, was about to begin.

Seeking to prevent this, President Warren G. Harding called the Washington Naval Conference in late 1921, with the goal of establishing limits on warship construction and tonnage. Convening on November 12, 1921, under the auspices of the League of Nations, the delegates met at Memorial Continental Hall in Washington DC. Attended by nine countries with concerns in the Pacific, the principal players included the United States, Great Britain, Japan, France, and Italy. Leading the American delegation was Secretary of State Charles Evan Hughes who sought to limit Japanese expansionism in the Pacific.

For the British, the conference offered an opportunity to avoid an arms race with the US as well as an opportunity to achieve stability in the Pacific which would provide protection to Hong Kong, Singapore, Australia, and New Zealand. Arriving in Washington, the Japanese possessed a clear agenda that included a naval treaty and recognition of their interests in Manchuria and Mongolia. Both nations were concerned about the power of American shipyards to out-produce them if an arms race were to occur.

As the negotiations commenced, Hughes was aided by intelligence provided by Herbert Yardley's "Black Chamber." Operated cooperatively by the State Department and US Army, Yardley's office was tasked with intercepting and decrypting communications between the delegations and their home governments. Particular progress was made breaking Japanese codes and reading their traffic. The intelligence received from this source permitted Hughes to negotiate the most favorable deal possible with the Japanese. After several weeks of meetings, the world's first disarmament treaty was signed on February 6, 1922.

The Washington Naval Treaty

The Washington Naval Treaty set specific tonnage limits on the signees as well as restricted armament size and expansion of naval facilities. The core of the treaty established a tonnage ratio that permitted the following:

  • United States: Capital Ships - 525,000 tons, Aircraft Carriers - 135,000 tons
  • Great Britain: Capital Ships - 525,000 tons, Aircraft Carriers - 135,000 tons
  • Japan: Capital Ships - 315,000 tons, Aircraft Carriers - 81,000 tons
  • France: Capital Ships - 175,000 tons, Aircraft Carriers - 60,000 tons
  • Italy: Capital Ships - 175,000 tons, Aircraft Carriers - 60,000 tons

As part of these restrictions, no single ship was to exceed 35,000 tons or mount larger than 16-inch guns. Aircraft carrier size was capped at 27,000 tons, though two per nation could be as large as 33,000 tons. In regard to onshore facilities, it was agreed that the status quo at the time of the treaty's signing would be maintained. This prohibited the further expansion or fortification of naval bases in small island territories and possessions. Expansion on the mainland or large islands (such as Hawaii) was permitted.

Since some commissioned warships exceeded the treaty terms, some exceptions were made for existing tonnage. Under the treaty, older warships could be replaced, however, the new vessels were required to meet the restrictions and all signatories were to be informed of their construction. The 5:5:3:1:1 ratio imposed by the treaty led to friction during negotiations. France, with coasts on the Atlantic and Mediterranean, felt that it should be permitted a larger fleet than Italy. They were finally convinced to agree to the ratio by promises of British support in the Atlantic.

Among the main naval powers, the 5:5:3 ratio was badly received by the Japanese who felt they were being slighted by the Western Powers. As the Imperial Japanese Navy was essentially a one-ocean navy, the ratio still gave them a superiority over the US and Royal Navy which had multi-ocean responsibilities. With the treaty's implementation, the British were forced to cancel the G3 and N3 programs and the US Navy was required to scrap some of its existing tonnages to meet the tonnage restriction. Two battlecruisers then under construction were converted into the aircraft carriers USS Lexington and USS Saratoga.

The treaty effectively stopped battleship construction for several years as the signatories attempted to design ships that were powerful, but yet still met the agreement's terms. Also, efforts were made to build large light cruisers that were effectively heavy cruisers or that could be up-converted with bigger guns in wartime. In 1930, the treaty was altered by the London Naval Treaty. This, in turn, was followed by the Second London Naval Treaty in 1936. This last treaty was not signed by Japanese as they had decided to withdraw from the agreement in 1934.

The series of treaties begun with the Washington Naval Treaty effectively ceased on September 1, 1939, with the beginning of World War II. While in place, the treaty did somewhat limit capital ship construction, however, the per vessel tonnage limitations were frequently flouted with most signatories either using creative accounting in computing displacement or outright lying about a vessel's size.

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Hickman, Kennedy. "Disarmament: Washington Naval Treaty." ThoughtCo, Apr. 5, 2023, thoughtco.com/disarmament-washington-naval-treaty-2361098. Hickman, Kennedy. (2023, April 5). Disarmament: Washington Naval Treaty. Retrieved from https://www.thoughtco.com/disarmament-washington-naval-treaty-2361098 Hickman, Kennedy. "Disarmament: Washington Naval Treaty." ThoughtCo. https://www.thoughtco.com/disarmament-washington-naval-treaty-2361098 (accessed June 5, 2023).