Washington Naval Treaty

• 1. Introduction

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  On the 6th of February 1922, five of the world's most powerful nations put their signatures to a document that would reshape naval warfare for two decades. The Washington Naval Treaty, also known as the Five-Power Treaty, bound the British Empire, the United States, Japan, France, and Italy to strict limits on the warships they could build. It was the first major international arms control agreement of the modern era, and it did not arrive quietly.

  The treaty grew out of a specific fear: that the Allied powers who had just fought a catastrophic world war together were now quietly preparing to fight each other. American plans drawn up between 1916 and 1919 called for a fleet of 50 modern battleships. Japan had authorized its own massive building program. Britain was sketching out yet more capital ships it could barely afford. The numbers threatened to spiral into an arms race that would exhaust all the nations involved, and possibly ignite a new conflict.

  What emerged from the Washington Naval Conference, which ran from November 1921 to February 1922, was something more complex and more fragile than a simple handshake. The treaty carried within it deep anxieties about national prestige, strategic survival, and industrial power. And one of the men who shaped its outcome had already worked out, with sobering clarity, exactly who would win if the agreement ever collapsed.

• 2. Seeds of the Race

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  Britain still held the world's largest and most powerful navy in the immediate aftermath of World War I, with the United States second and Japan a more distant third. Yet within months of the armistice, the strategic picture had shifted in ways that made old alliances feel fragile.

  The fate of the defeated German High Seas Fleet became an early flashpoint. France and Italy wanted the German ships divided among the victors. Britain and the United States wanted them destroyed. The argument became largely academic on the 21st of June 1919, when German crews scuttled most of their own fleet. The French were furious, particularly unimpressed with the British explanation that the Royal Navy vessels guarding the Germans had been away on exercises at the time. No credible evidence ever emerged that Britain had collaborated in the scuttling, but the suspicion colored later negotiations.

  A week after the scuttling, on the 28th of June 1919, the Treaty of Versailles imposed strict limits on the sizes and numbers of warships the new German government could build. That constraint removed Germany as a threat, but it also removed the common enemy that had kept the Allies united. US President Woodrow Wilson's administration had already announced successive expansion plans for the American navy. In 1920, the Japanese Diet finally authorized the "eight-eight" programme, which called for eight modern battleships and eight battlecruisers. Britain's 1921 Naval Estimates planned four battleships and four battlecruisers, with four more battleships the following year.

  The American public and Congress had little appetite for this spending. The 1920 presidential election swung political momentum back toward non-interventionism. Britain, meanwhile, was deep in a post-war recession and could ill afford the cost of capital ships. When the United States learned in late 1921 that Britain was planning its own conference on Pacific and Far East strategy, the Harding administration moved quickly to call the Washington Naval Conference first, both to forestall the British initiative and to satisfy domestic demand for a global disarmament effort.

• 3. Hughes at the Podium

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  At the first plenary session on the 21st of November 1921, US Secretary of State Charles Evans Hughes delivered what became the conference's defining moment. His opening was blunt: "The way to disarm is to disarm." The line received enthusiastic public endorsement and likely helped push the negotiations toward a faster and more favorable conclusion than might otherwise have occurred.

  Hughes then laid out a set of proposals that stunned the assembled delegations. He called for a ten-year "holiday" on the construction of capital ships, meaning an immediate stop to all battleship and battlecruiser building. He proposed scrapping existing and planned ships to produce a tonnage ratio of 5:5:3:1.67:1.67 among Britain, the United States, Japan, France, and Italy. Ongoing limits on both capital ship tonnage and secondary vessel tonnage would maintain that same 5:5:3 ratio going forward.

  The British delegation found the proposals largely acceptable, though they provoked outrage among parts of the Royal Navy. Britain could no longer simultaneously maintain adequate fleets in the North Sea, the Mediterranean, and the Far East. For many naval officers, the treaty meant accepting a permanent reduction in British sea power. Yet the pressure to agree was enormous: the risk of war with the United States was regarded as increasingly theoretical, continued naval spending was unpopular across the empire, and the post-war recession had forced major budget cuts.

  France presented a different challenge. The French delegation initially demanded 350,000 tons for their capital ships, slightly above the Japanese limit, rather than the 175,000 tons Hughes proposed. A major British demand, the complete abolition of submarines, ran directly into French opposition; France insisted on an allowance of 90,000 tons of submarines, and the conference ultimately ended without any agreement to restrict submarine construction at all.

• 4. Japan's Internal Fracture

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  The Japanese delegation arrived in Washington divided against itself, and the fault line ran through the question of what the 5:5:3 ratio actually meant for Japan's survival.

  Japanese naval doctrine required a fleet at least 70% the size of the American navy, calculated as the minimum force needed to defeat the United States in a conflict. The strategy rested on a two-battle sequence: first destroying the US Pacific Fleet, then taking on the US Atlantic Fleet before it could respond. A fleet ratio of 3:5 was unacceptable because, in that first Pacific engagement, Japan would face a 6:5 disadvantage, which naval planners believed was not enough margin to guarantee victory. At the start of the negotiations, Japan possessed only 55% of the capital ships and 18% of the GDP of the Americans.

  Katō Tomosaburō, the director of the Japanese delegation, understood these numbers and drew a different conclusion than his opponents. He preferred to accept the 3:5 ratio rather than risk an arms race that Japan's relative industrial weakness made unwinnable, and that could trigger an economic crisis. Opposed to him was Katō Kanji, the president of the Naval Staff College and chief naval aide at the delegation, who represented what was called the "big navy" view: that Japan had to prepare as thoroughly as possible for what he regarded as an inevitable conflict with the United States.

• 5. The Terms in Detail

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  The final treaty imposed a precise architecture of limits. Capital ships were capped at 35,000 tons standard displacement and guns no larger than 16 inches in calibre. Aircraft carriers were limited to 27,000 tons and could carry no more than ten heavy guns of a maximum 8-inch calibre. Each signatory was permitted to convert two existing capital ship hulls into aircraft carriers, with a displacement limit of 33,000 tons each. Carriers already in service or under construction, including the Argus, Eagle, Furious, Hermes, Langley, and Hosho, were declared "experimental" and could be replaced without regard to age.

  All other warships were held to a maximum of 10,000 tons displacement and 8-inch guns. The idea of limiting total cruiser numbers or aggregate tonnage was rejected entirely after British and French objections. What emerged instead was a qualitative ceiling: the 10,000-ton, 8-inch-gun limit was designed to allow Britain to retain the Hawkins class it was already building, and it coincidentally matched American requirements for Pacific operations and Japanese plans for the Furutaka class.

  In tonnage terms, the British Empire and the United States each received 525,000 tons of capital ships and 135,000 tons of aircraft carriers. Japan was allotted 315,000 tons of capital ships and 81,000 tons of carriers. France and Italy each received 175,000 tons of capital ships and 60,000 tons of carriers. The United States had to scrap 30 existing or planned capital ships, Britain 23, and Japan 17. Article XIX added a restriction that Britain, Japan, and the United States could build no new fortifications or naval bases in the Pacific, with existing installations in Singapore, the Philippines, and Hawaii permitted to remain. That clause was central to winning Japanese acceptance: newly fortified British or American bases in the Pacific would have made Japan's strategic position untenable.

• 6. Loopholes and Violations

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  Almost as soon as the ink was dry, the treaty's signatories began probing its edges.

  Japan built the light aircraft carrier Ryujo specifically to exploit the treaty's definition of an aircraft carrier as a vessel displacing more than 10,000 tons. A carrier below that threshold would not count against the tonnage limits. The ship proved too small to be fully capable and was later expanded past 10,000 tons. The London Naval Treaty subsequently closed that loophole, and no other power attempted the same approach.

  The United States found a different angle. When converting two battlecruisers into carriers, the ships came in overweight relative to the 33,000-ton conversion limit. American officials argued that because the vessels were being built from scratch as carriers, rather than simply modified, they qualified as ships being "reconstructed" and could carry an additional 3,000 tons for anti-air and anti-submarine defenses. No other power ever made that argument. The British Nelson class exploited the treaty's tonnage definition more quietly: since the treaty excluded fuel and reserve boiler feed water from displacement calculations, the Nelson's designers built torpedo defenses using liquid layers that doubled as reserve boiler feed water, keeping that weight off the official tonnage count.

  France went further than loophole-seeking. In 1935, the French Navy laid down a new battleship that, combined with two others under construction, pushed total French battleship tonnage beyond the 70,000-ton limit. A keel laid in December 1936, less than three weeks before the treaty expired, added another 35,000 tons of violation. The French government dismissed British objections by pointing to the Anglo-German Naval Agreement of 1935, which Britain had signed unilaterally and which dismantled the disarmament clauses of the Treaty of Versailles. Italy repeatedly misrepresented the displacement of its ships to remain on paper within the treaty limits, even as ships built in the late 1920s and early 1930s exceeded the 10,000-ton ceiling, and vessels of the mid-1930s carried standard displacements in excess of 40,000 tons.

• 7. Yamamoto and the Cipher Bureau

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  Two pieces of context, both invisible to most of the delegates at the time, shaped the treaty's final form in ways that only became clear later.

  Isoroku Yamamoto, who would later plan the attack on Pearl Harbor, was among those who argued that Japan should remain within the treaty framework. His reasoning was precise: he had served at the Japanese embassy in Washington and had seen the auto factories in Detroit and the oil fields in Texas. He observed directly that Japan lacked the productive capacity for a naval race with America. After the treaty was signed, he commented that "the ratio works very well for Japan; it is a treaty to restrict the other parties." He believed Japan would need methods other than mass construction to equalize the odds, a perspective that would eventually lead toward the December 1941 operation he masterminded.

  What none of the delegates knew was that the American "Black Chamber," the Cypher Bureau commanded by Herbert Yardley, had been intercepting and deciphering the communications of multiple delegations throughout the conference. Japanese cables in particular were read thoroughly. American negotiators therefore knew the absolute minimum concession the Japanese government would accept before it would walk away from the table. The gap between what Japan publicly demanded and what it would privately accept was known in advance to the other side.

  The treaty's provisions formally remained in force until the end of 1936, after Japan gave notice on the 29th of December 1934 that it intended to terminate the agreement. The controversy the treaty generated within the Imperial Japanese Navy, between the Treaty Faction officers and the Fleet Faction aligned with ultranationalists, was itself partly a product of the suspicion that Japanese negotiators had been out-maneuvered; the value accepted had seemed too low to too many senior officers, and the reason was one that could not be acknowledged publicly for decades.

• 8. Aftermath and Legacy

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  The Washington Naval Treaty marked the end of a period of continuous battleship construction that had defined naval strategy for a generation. Ships that had been laid down or planned were scrapped or converted into aircraft carriers, a change that would reshape the nature of naval combat in the following decades.

  The London Naval Treaty of 1930 modified the Washington terms and extended limits to cruisers, destroyers, and submarines. The Second London Naval Treaty of 1936 attempted to extend the Washington framework until 1942, but without Japan or Italy as signatories, it was largely ineffective. By the mid-1930s, the treaty order was dissolving. Germany renounced the relevant clauses of the Treaty of Versailles through the Anglo-German Naval Agreement of 1935. Japan gave its formal notice of withdrawal at the end of 1934. Italy continued building ships that violated displacement limits while misreporting the figures.

  The treaty also produced consequences that were never written into it. American delegates had made clear they would not agree to the Washington Treaty unless Britain ended the Anglo-Japanese Alliance. The 1921 Imperial Conference had already voted not to renew that alliance, and the Royal Navy's regrouping in 1921 had pulled British ships from the South Pacific. That withdrawal weakened Britain's longstanding ally Chile and increased American influence across the Americas, indirectly encouraging Peruvian and Bolivian diplomatic pressure against Chile. A naval arms agreement negotiated in Washington had, through a chain of strategic repositioning, altered the balance of power in South America. The treaty's designers had not anticipated that particular consequence, but it followed directly from the decisions made in those rooms in the winter of 1921-22.