The Washington Naval Treaty

After world powers signed the 11 November 1918 Armistice, effectively ending World War I, the British Royal Navy interned the German High Seas Fleet, which had surrendered mostly intact. Allied powers held opposing views concerning the fate of the German warships then moored at the Royal Navy base at Scapa Flow. French and Italian leaders argued the captured ships should be divided among the victorious Allies, while the Americans and British insisted on destroying the entire fleet.[1] On 21 June 1919, before the Allies could agree upon a course of action, and mere days before the signing of the Treaty of Versailles on 28 June, German sailors settled the issue by scuttling the majority of the ships on the harbor bottom.[2]

In many ways, the sunken German ships at Scapa Flow are symbolic of the post-1918 anti-militarist movement. The war-weary voting public in Western democracies, which now included women voters, was fearful of new arms races and the implementation of large, peace-time military budgets.[3] In each of these countries, the public viewed pre-war land and sea arms races as major contributing factors to the outbreak of war. Indeed, all the victorious countries - the US, Great Britain, Japan, France, and Italy - all had political and economic reasons to avoid another international arms race, especially one between themselves. Financial concerns played the largest role, France and Italy in particular could ill afford to spend large amounts of money on warships when they had extensive war damage to repair in their own countries. [4] While Great Britain, the strongest naval power in the world, did not view France and Italy as serious threats, there was considerable concern regarding Japan and the United States, whose economies were far less negatively affected by the war and had not stopped building capital ships post armistice.[5] Japan, concerned with its growing population, chronic economic difficulties, and the lack of raw materials needed to support imperial expansion, also saw concrete benefits for avoiding an arms race.[6]

In the United States, the war had created an economic boom, but the postwar economy collapsed and the country fell into a deep recession, making a reduction of military spending popular among the voting public. Candidates running for office in the 1920 Presidential and Congressional elections responded to public pressure to prioritize domestic interests at the expense of military concerns. Even though Woodrow Wilson was not running for re-election, voters rejected the President’s agenda, including his advocacy for joining the League of Nations and his 1919 proposal to expand the Navy.[7] Wilson’s shipbuilding proposal would have added more than 50 first-line vessels to the US fleet, surpassing the British Navy.[8] Because Wilson’s domestic and foreign policy plans stood against the prevailing non-interventionist sentiment of the time, his final years in office ultimately weakened the candidacy of the Democratic nominee for President, James Cox, who lost to Republican Warren G. Harding. 

Newly-elected President Harding, who had campaigned on a “return to normalcy” and opposition to US membership in the League of Nations, saw an opportunity to build political capital by championing the popular cause of arms limitation. In 1921, Harding’s Secretary of State, Charles Evans Hughes, convened the Washington Naval Conference, the first major post-war international meeting on naval disarmament. Facing similar issues with popular rejection of high defense spending and militarism, Britain, France, and Italy were also open to a conference to limit the brewing naval arms race, anticipating the resulting electoral and bureaucratic advantages.[9] The 10-week Conference produced three major treaties: the Five-Power Treaty, the Four-Power Treaty, and the Nine-Power Treaty. Treaty signatories included Great Britain, the US, Japan, France, and Italy, with Belgium, China, Portugal, and the Netherlands participating in a limited capacity. Believing that the Treaty of Versailles had already settled the matter of German disarmament, the conveners excluded Germany.[10]

Signed by the United States, Great Britain, Japan, France, and Italy, the Five-Power Treaty was the foundation of the naval disarmament accords resulting from the Washington Naval Conference. Among the chief agreements of the treaty was the obligation of each of the signatories to adhere to a tonnage ratio for warships (defined by the treaty as dreadnought battleships and battlecruisers). Articles IV and VII of the treaty set the ratio to 5:5:3, allotting the US and UK 500,000 tons each and Japan 300,000 tons. The articles apportioned France and Italy 175,000 tons each, or 1 and 3/4 of the ratio.[11] With tonnage ratios for battleships set below existing levels, most of the signatories decommissioned and scrapped large numbers of battleships, which met the politicians’ goal of saving money. A perhaps unintended consequence of this stipulation was that it encouraged signatories to convert some battleship or battlecruiser hulls into aircraft carriers rather than scrapping them.[12]

With regards to aircraft carriers (defined as a warship designed exclusively for launching and landing aircraft), the Five-Power Treaty allotted the US and Great Britain 135,000 tons each, Japan 81,000 tons, and France and Italy 60,000 tons each. For the US, the Five-Power Treaty limited each individual aircraft carrier to 27,000 tons and a maximum of 10 heavy guns.[13] Articles IX and X of the treaty allowed each signatory to utilize the hulls of two already-existing capital ships for aircraft carriers, each limited to a displacement of 33,000 tons.[14] Article VIII of the Five-Power Treaty allowed for aircraft carriers that were already in service or in the process of being built, including Argus, Eagle, Furious, Hermes, Langley, and Hōshō, to be considered “experimental” and thus exempted in the treaty’s limitations of aircraft carriers.[15] Since most battleship tonnage was already mostly full, and aircraft carrier tonnage mostly empty, these clauses of the Five-Power Treaty played a significant role in encouraging construction of aircraft carriers and their later ascendance in twentieth-century naval warfare. 
The Five-Power Treaty granted the US and Great Britain the largest portion of the tonnage ratio because the two countries had colonies and significant economic and security interests in both the Atlantic and Pacific. Moreover, Article XIX explicitly maintained the status quo of American and British naval supremacy. In addition to establishing tonnage ratios, the Five-Power Treaty also curtailed American, British, and Japanese expansion in the Pacific.[16] These constraints, along with the limits enshrined in Articles IV and VII, would prove the most controversial over time. Of all the powers, Japan was the most impacted by the treaty and bitterly opposed those clauses, arguing they unfairly restricted Japanese military and economic development in Asia and the Pacific. Unable to sway the other parties, however, Japan was forced to concede to these restrictions when the treaty was signed on 6 February 1922.

In consideration of overall tonnage and tighter budget constraints, navies around the world focused less on the development of heavily armored surface combatants (although they were often modernized), and more on alternative ways to project power at sea. The three major naval powers therefore spent much of the 1920s and 1930s experimenting with aircraft carrier construction, operations, and doctrine in ways that reflected the stipulations of the Washington Naval Treaty. In accordance with the treaty, the US Navy converted the collier Jupiter into the service’s first experimental aircraft carrier, Langley, which was recommissioned in 1922. Originally classified as battle cruisers, Lexington and Saratoga, were completed as carriers and commissioned in 1927. In 1931, the US built its first ship designed from inception as an aircraft carrier, the 15,000-ton Ranger.[17] Yorktown and Enterprise, laid down in 1934 and commissioned in 1937 and 1938, respectively, were highly successful designs that would influence the development of later carrier classes.[18] The final treaty-limited American aircraft carrier was Wasp, laid down in 1936 and commissioned in 1930.[19]

At the time of the treaty, the Royal Navy had two carriers under construction, Eagle and Hermes. Laid down in 1918 as a battleship, the British converted Eagle into a carrier to meet treaty requirements.[20] Hermes, also laid down in 1918, was the first British carrier built from the keel up. In 1924, the Royal Navy began converting two light battlecruisers, Courageous and Glorious, into carriers, completing both conversions by 1930. Ark Royal, laid down in 1935, is considered the first modern British carrier.[21]

The Imperial Japanese Navy’s first effective carriers were converted from the battlecruiser hulls Akagi and Kaga. Both ships were reconstructed between 1934 and 1938 to increase their aircraft carrying capacity. Laid down in 1929, the Japanese also built the small aircraft carrier Ryūjō, but design flaws meant she had to undergo a number of modifications to improve seaworthiness and stability. Improving on these shortcomings by the mid-1930s, the Japanese Navy ordered the construction of two fleet carriers, Sōryū and Hiryū, as well as two more light carriers, Shōhō and Zuihō. All played important roles during the early years of the Pacific War.[22]

The unraveling of the Washington Naval Treaty accords was a protracted process. Problematic loopholes in the treaty created the need for subsequent conferences. In 1927, the signatories of the Washington Naval Treaty attempted to reconvene at the Geneva Naval Conference to deal with the proliferation of cruisers, destroyers, and submarines, an issue left unresolved during the initial meeting.[23] Negotiations in Geneva failed, however, because Italy and France refused to participate and the attendees could not reach an agreement on the distribution of light naval tonnage.[24] Coming on the heels of global economic retrenchment following stock market crashes in 1929, the London Naval Treaty of 1930 represented a second attempt to limit naval spending.[25] Signed by the US, Great Britain, Japan, France, and Italy on 22 April 1930, and set to be renewed in 1936, the treaty succeeded in creating tonnage limitations for surface warships, regulated submarine warfare, and further limited the construction of cruisers and destroyers. These accords, however, proved to be short-lived.[26]
Japan, after having invaded Manchuria, gave a formal notice of intent in 1934 that it would not sign the London Naval Treaty when it came up for renewal.[27] At the same time, Germany began rebuilding its navy.[28] The latter pushed the British to negotiate a bi-lateral treaty with Germany - the Anglo-German Naval Agreement of 1935 – that effectively dismantled the naval disarmament clauses of the Treaty of Versailles.[29] While the US, Britain, the Commonwealth, and France signed the Second London Naval Treaty in 1936 to try to keep naval spending limited, it too began showing cracks when Italy withdrew, after having been sanctioned by the League of Nations after invading Ethiopia in 1935.[30]

Although there was no real danger of a significant German or Italian aircraft carrier program, the Japanese were different. In 1937 and 1938, Japan laid down two 25,000 ton fleet carriers, Shōkaku and Zuikaku. Without having to accommodate treaty limitations, these Japanese aircraft carriers successfully balanced aircraft capacity, speed, and defensive armament.[31] At the same time, Italy had begun building heavy battleships that exceeded the terms of treaty limitations, which encouraged the French to do the same.[32] Given that other powers had already built beyond treaty limits, in 1938 the US Congress authorized the construction of Hornet, an additional Yorktown-class aircraft carrier, and the Navy accelerated a new design for the 30,000-ton Essex-class.[33]

International disarmament efforts unraveled in parallel with the demise of the League of Nations, which had obligated its members to restrict "armaments to the lowest point consistent with national safety and the enforcement by common action of international obligations."[34] By the mid-1930s, global efforts to slow various Great Power arms races had collapsed, leaving no strong international agreements in place to limit rearmament in the run-up to the Second World War.