Washington Naval Treaty: Arms Control and Naval Disarmament

Introduction: The Five-Power Treaty and Post-War Naval Competition

The Washington Naval Treaty, popularly known as the Five-Power Treaty, was a landmark agreement involving the major powers following their victory in World War I. The treaty's terms and conditions focused on preventing an arms race by controlling and limiting naval construction. Negotiations at the Washington Naval Conference, held between 1921 and 1922, resulted in an agreement among the governments of Japan, the United Kingdom, the United States, Italy, and France. The agreement specifically limited the overall construction of battleships, aircraft carriers, and battle cruisers among the signatories. Other warship categories—such as cruisers, destroyers, and submarines—were not directly constrained but were capped at 10,000 tons in displacement. Subsequent treaties included additional naval arms limitation conferences that sought to expand warship-building restrictions further. The Washington Treaty terms were later modified through the London Naval Treaty of 1930 and the Second London Naval Treaty of 1936. However, during the 1930s, Italy and Japan renounced these treaties, creating an untenable position for the remaining signatories who wished to maintain the agreements.

The Naval Arms Race: Britain, the United States, and Japan

After World War I, the United Kingdom's navy emerged as the largest and most powerful in the world, followed by that of the United States and Japan. Although these nations had been allied during World War I, a naval arms race appeared to be a real possibility in the following years. The competition began with the United States. President Woodrow Wilson's administration announced successive plans for expanding the U.S. Navy between 1916 and 1919, resulting in massive fleets of modern battleships. During this period, there was intense engagement in building more battleships and battle cruisers.

In response, the Japanese parliament authorized construction of additional warships to enable the Japanese Navy to achieve its "eight-eight" fleet program, which called for eight modern battle cruisers and eight battleships. To this end, the Japanese continued work on four battle cruisers and four battleships that were larger and more powerful than those of preceding classes. Meanwhile, the British Naval Estimates of 1921 planned to establish and maintain four battle cruisers and four battleships, followed by additional battleships in subsequent years. This competitive spiral made some form of arms limitation agreement increasingly urgent.

Charles Evans Hughes and the Disarmament Proposals

In the initial plenary session of 1921, Charles Evans Hughes, the U.S. Secretary of State, presented the proposals of the United States. Hughes made a dramatic start for the conference with controversial statements aimed at achieving active disarmament. This ambitious goal attracted enthusiastic public endorsement, and the efficient pace of the conference helped ensure that the United States' proposals were adopted. Hughes proposed a ten-year "holiday" or pause in the construction of capital ships (battlecruisers and battleships), including immediate suspension of all capital ship building. The conference also proposed the scrapping of planned or existing capital ships, with an arrangement that gave the United States, Japan, and Italy higher tonnage allowance ratios compared to Britain and France. These capital ship tonnage limits were established at the famous 5:5:3 ratios.

Treaty Limitations: Tonnage, Firepower, and Construction Controls

The Washington Treaty imposed strict limitations on both the construction and tonnage of aircraft carriers and capital ships, with controls extending to the specifications of individual vessels. The tonnage limitations established in Articles VII and IV of the treaty set strength ratios of approximately 5:5:1.75:3:1.75 among the United States, Britain, Japan, France, and Italy respectively. In addition, capital ships—battlecruisers and battleships—were subject to qualitative limits for each individual ship. These were limited to a standard displacement of 35,000 tons, with guns not to exceed 16-inch caliber, as specified in Articles V and VI.

Aircraft carriers faced limitations of 27,000 tons and could carry no more than ten heavy guns (with a maximum caliber of 8 inches). However, signatories were permitted to convert two existing ship hulls into aircraft carriers, each with a displacement limit of 33,000 tons. All subsequent warships were limited to a maximum displacement of 10,000 tons and a maximum gun caliber of 8 inches, according to Articles XI and XII. The Treaty's articles detailed in Chapter II specified which individual ships each navy could retain—for example, the United States was allowed to complete two further ships of the West Virginia class, while Britain was authorized to complete two additional ships within the treaty limits. Part 2 of Chapter II outlined the actions required to render ships ineffective for military use, including sinking or scrapping. The provisions also limited the number of ships that could be converted to training vessels or target ships, requiring that their armor, armament, and other combat-essential components be completely removed before they could be converted into aircraft carriers.