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Guns from battleships being scrapped in Philadelphia Navy Yard during December 1923. USS South Carolina being dismantled in the background.

The Washington Naval Treaty, also known as the Five-Power Treaty, was a treaty among the major nations that had won World War I, which by the terms of the treaty agreed to prevent an arms race by limiting naval construction. It was negotiated at the Washington Naval Conference, which was held in Washington, D.C. from November 1921 to February 1922, and signed by the governments of the United Kingdom, the United States, Japan, France, and Italy. It limited the construction of battleships, battlecruisers and aircraft carriers by the signatories. The numbers of other categories of warships, including cruisers, destroyers and submarines, were not limited by the treaty but were limited to 10,000 tons displacement.

Subsequent to the treaty were a number of other naval arms limitation conferences that sought to increase limitations of warship building. The terms of the Washington treaty were modified by the London Naval Treaty of 1930 and the Second London Naval Treaty of 1936. By the mid-1930s, Japan and Italy renounced the treaties, making naval arms limitation an increasingly untenable position for the other signatories.


Immediately after World War I, the United Kingdom had the world's largest and most powerful navy, followed by the United States and more distantly by Japan. The three nations had been allied for the First World War, but a naval arms race seemed likely for the next few years.[1] This arms race began in the US. President Woodrow Wilson's administration announced successive plans for the expansion of the US Navy during 1916 and 1919 that, if completed, would result in a massive fleet of 50 modern battleships;[2] currently it was engaged in building six battleships and six battlecruisers. In response, the Japanese parliament finally authorised construction of warships to enable the Japanese Navy to reach its target of an "eight-eight" fleet programme, with eight modern battleships and eight battlecruisers. To this end, the Japanese started work on four battleships and four battlecruisers, all much larger and more powerful than those of the classes preceding.[3]

While the British Royal Navy retained numerical superiority prior to the treaty, most of its ships were old and deteriorated after much use during the war; very few matched the new US or Japanese designs. The 1921 British Naval Estimates planned four battleships and four battlecruisers, with another four battleships to follow the subsequent year.[1]

This "arms race" was widely unwelcome. The US Congress in fact disapproved Wilson's 1919 plan, and for the 1920 presidential election, US politics resumed the prewar isolationism, with little endorsement for continued naval expansion.[4] Britain could ill afford any resumption of battleship construction, given the exorbitant price of naval construction.[5]

During late 1921, the US government became aware that Britain was planning a conference to discuss the strategic situation in the Pacific and Far East. To forestall the conference and to satisfy domestic pressure for a global disarmament conference, the Harding administration called the Washington Naval Conference during November 1921.[6]


At the first plenary session held November 21, 1921, the US Secretary of State, Charles Evans Hughes, presented the US proposals. Hughes provided a dramatic beginning for the conference by stating with resolve: "The way to disarm, is to disarm."[7] The ambitious slogan received enthusiastic public endorsement and likely shortened the conference while helping ensure the US proposals were largely adopted. He subsequently proposed the following:

  • A ten-year pause or "holiday" in the construction of capital ships (battleships and battlecruisers), including the immediate suspension of all capital ship building.
  • The scrapping of existing, or planned, capital ships so as to give a 5:5:3:1.75:1.75 ratio of tonnage between the US, Britain, Japan, France and Italy.
  • Ongoing limits of both capital ship tonnage, and the tonnage of secondary vessels, with the 5:5:3 ratio.

Capital ships

The proposals regarding capital ships were largely accepted by the British delegation, though they were controversial with the public. The Hughes plan meant the abandonment of Britain's long dominance of the sea. In particular, it would no longer be possible for Britain to have adequate fleets in the North Sea, the Mediterranean and the Far East simultaneously. These facts provoked outrage from parts of the Royal Navy. Nevertheless, there was huge pressure on Britain to agree. The risk of war with the US was increasingly regarded as merely theoretical, as there were very few policy differences between the two countries. Neither was increasing naval spending popular in either Britain or its dominions. Furthermore, Britain was implementing major decreases of its budget due to the economic crisis created by the end of the War.[8]

The Japanese delegation was divided. Japanese naval doctrine required the maintenance of a fleet 70% the size of that of the US, which was felt to be the minimum necessary to defeat the US in any subsequent war; (the Japanese envisaged two separate engagements, first with the US Pacific Fleet, then with the Atlantic Fleet and calculated that a 7:5 ratio in the first battle would produce a big enough margin of victory to be able to win the subsequent engagement) thus a 5:3 ratio, or 60%, was unacceptable. Nevertheless, the director of the delegation, Katō Tomosaburō, favoured accepting a 60% ratio to the prospect of an arms race with the US, as the relative industrial output of the two nations would cause Japan to lose such an arms race and might cause an economic crisis as a consequence.

His opinion was opposed strongly by Katō Kanji, the president of the Naval Staff College, who acted as his chief naval aide at the delegation, and who represented the influential "big navy" school of thought. This school of thought held that in the event of war the USA would be able to build indefinitely more warships, given its huge industrial power, and Japan thus needed to prepare as thoroughly as possible for the inevitable conflict with America. Katō Tomosaburō was finally able to persuade the Japanese high command to accept the Hughes proposals, but the outcome of the Treaty was a cause of controversy in the Japanese navy for years to come.[9]

The French delegation initially responded angrily to the idea of reducing their capital ships tonnage to 175,000 tons and demanded 350,000, slightly above Japan. In the end, concessions regarding cruisers and submarines helped persuade the French to agree to the limit on capital ships.[10]

There was much discussion about the inclusion or exclusion of individual warships. In particular, the Japanese delegation was keen to retain their newest battleship, Mutsu, which had been funded with great public enthusiasm, including donations from schoolchildren.[11] This resulted in provisions to allow the US and Britain to construct equivalent ships.

Cruisers and destroyers

Secretary Hughes proposed to limit secondary ships (cruisers and destroyers) in the same proportions as capital ships. However, this was unacceptable to both the British and the French. The British counterproposal, in which the British would be entitled to 450,000 tons of cruisers in consideration of their global imperial commitments but the US and Japan only 300,000 and 250,000 respectively, proved equally contentious. Thus, the idea of limiting cruiser tonnage or numbers was rejected entirely.[10]

Instead, the British suggested a qualitative limit of future cruiser construction. The limit proposed, of a 10,000 ton maximum displacement and 8-inch calibre guns, was intended to allow the British to retain the Hawkins class then being constructed. This coincided with US requirements for cruisers for Pacific operations, and also with Japanese plans for the Furutaka class. So this suggestion was adopted with little debate.[10]


A major British demand during the negotiations was the complete abolition of the submarine, the weapon that had nearly defeated Britain during World War I. However, this proved impossible, particularly as a result of French opposition; the French demanded an allowance of 90,000 tons of submarines,[12] and the conference ended without agreement on restricting submarines.

Pacific bases

Article XIX of the Treaty also prohibited Britain, Japan and the US from constructing any fortifications or naval bases in the Pacific. This was a significant victory for Japan, as fortified British or American bases would pose a serious problem for the Japanese in the event of any future war. This clause of the Treaty essentially guaranteed Japan would be the dominant power in the Western Pacific[13] and was crucial in gaining Japanese acceptance of the limits on capital ship construction.


Tonnage limitations
Country Capital ships Aircraft carriers
British Empire 525,000 long ton
(533,000 tonnes)
135,000 tons
(137,000 tonnes)
United States 525,000 tons
(533,000 tonnes)
135,000 tons
(137,000 tonnes)
Empire of Japan 315,000 tons
(320,000 tonnes)
81,000 tons
(82,000 tonnes)
France 175,000 tons
(178,000 tonnes)
60,000 tons
(61,000 tonnes)
Italy 175,000 tons
(178,000 tonnes)
60,000 tons
(61,000 tonnes)

The Treaty strictly limited both the tonnage and construction of capital ships and aircraft carriers, and also included limits of the size of individual ships.

The tonnage limits defined by Articles IV and VII (tabulated) gave a strength ratio of approximately 5:5:3:1.75:1.75 between Britain, the USA, Japan, Italy and France.

The qualitative limits of each type of ship were as follows;

  • Capital ships (battleships and battlecruisers) were limited to 35,000 tons standard displacement and guns of no larger than 16-inch calibre. (Articles V and VI)
  • Aircraft carriers were limited to 27,000 tons and could carry no more than 10 heavy guns, of a maximum calibre of 8 inches. However, each signatory was allowed to use two existing capital ship hulls for aircraft carriers, with a displacement limit of 33,000 tons each. (Articles IX and X) For the purposes of the treaty an aircraft carrier was defined as a warship displacing more than 10,000 tonnes and exclusively constructed for launching and landing aircraft. Carriers lighter than 10,000 tonnes therefore did not count towards the tonnage limits. (Article XX, part 4)
  • All other warships were limited to a maximum displacement of 10,000 tons and a maximum gun calibre of 8 inches. (Articles XI and XII).

The Treaty also detailed by Chapter II which individual ships were to be retained by each Navy, including the allowance for the USA to complete two further ships of the West Virginia class and for Britain to complete two new ships in accordance with the Treaty limits. Chapter II, part 2, detailed what was to be done to render a ship ineffective for military use; in addition to sinking or scrapping, a limited number of ships could be converted as target ships or training vessels, so long as their armament, armour and other combat-essential parts were removed completely; some could also be converted into aircraft carriers. Part 3, Section II of the Treaty specified which ships were to be scrapped to comply with the Treaty, and when the remaining ships could be replaced. In all the USA had to scrap 30 existing or planned capital ships; Britain, 23; and Japan, 17.


The effect of the Treaty was to arrest the continuing upward trend of battleship size, and to halt new construction entirely for more than a decade.

The Washington Treaty marked the end of a long period of increases of battleship construction. Many ships currently being constructed were scrapped or converted into aircraft carriers. The Treaty limits were respected, and then extended by the London Naval Treaty of 1930. It was not until the mid-1930s that navies began to build battleships once again, and the power and size of new battleships began to increase once again. The London Naval Treaty of 1936 sought to extend the Washington Treaty limits until 1942, but in the absence of Japan or Italy was largely ineffective. The effects on cruiser building were less fortunate. While the Treaty specified 10,000 tons and 8-inch guns as the maximum size of a cruiser, in effect this was also the minimum size cruiser that any navy was willing to build. The Treaty began a building competition of 8-inch, 10,000 ton "treaty cruisers"[14] which gave further cause for concern. Subsequent Naval Treaties sought to address this, by limiting cruiser, destroyer and submarine tonnage.

Japanese denunciation

Japanese denunciation of the Washington Naval Treaty, 29 December 1934.

The naval treaty had a profound effect on the Japanese. With superior American and British industrial power, a long war would very likely end in a Japanese defeat. Thus, gaining parity on the strategic level was not economically possible.

Many Japanese considered the 5:5:3 ratio of ships as another way of being snubbed by the West (though it can be argued that the Japanese, having a one-ocean navy, had a greater concentration of force than the two-ocean United States Navy or the three-ocean Royal Navy). It also contributed to controversy in high ranks of the Imperial Japanese Navy between the Treaty Faction officers and those opposed to it, who were also allied with the ultranationalists of the Japanese army and other parts of the Japanese government. For Treaty Faction opponents, the Treaty was one of the factors which contributed to the deterioration of the relationship between the United States and Japanese governments. The perception of unfairness resulted in Japan's renunciation of the Naval Limitation Treaties during 1936. Isoroku Yamamoto, who later masterminded the Pearl Harbor attack, argued that Japan should remain party to the treaty and was therefore regarded by many as a member of the "Treaty Faction". His opinion was more complex, however, in that he believed the United States could out-produce Japan by a greater factor than the 5:3 ratio because of the huge US production advantage, concerning which he was an expert, having served with the Japanese Embassy in Washington. He believed that other methods would be needed to even the odds, which may have contributed to his advocacy of the plan to attack Pearl Harbor. However, he did not have sufficient influence at Navy headquarters or in the government.

On 29 December 1934, the Japanese government gave formal notice that it intended to terminate the treaty. Its provisions remained in force until the end of 1936, and it was not renewed, Japan effectively ignoring the treaty during 1936.

Cryptanalytic influences on the treaty

What was unknown to the participants of the Conference was that the American "Black Chamber" (the Cypher Bureau, a US intelligence service), commanded by Herbert Yardley, was spying on the delegations' communications with their home capitals. In particular, Japanese communications were penetrated thoroughly, and American negotiators were able to get the minimum possible deal the Japanese had indicated they would accept, less than which they would renounce the Conference. As this ratio value was unpopular with much of the Imperial Japanese Navy and with the increasingly active and important ultranationalist groups, the value the Japanese Government accepted was the cause of much suspicion and accusation among Japanese politicians and Naval officers.[citation needed]


  1. 1.0 1.1 Marriot 2005, p. 9.
  2. Potter 1981, p. 232.
  3. Evans & Peattie 1997, p. 174.
  4. Potter 1981, p. 233.
  5. Kennedy 1983, p. 274.
  6. Marriot 2005, p. 10.
  7. Jones 1981, p. 119.
  8. Kennedy 1983, p. 275–6.
  9. Evans & Peattie 1997, p. 193–96.
  10. 10.0 10.1 10.2 Marriot 2005, p. 11.
  11. Evans & Peattie 1997, p. 197.
  12. Marriot 2005, p. 10–11.
  13. Evans & Peattie 1997, p. 199.
  14. Marriot 2005, p. 3.


  • Evans, David; Peattie, Mark (1997). "Kaigun: Strategy, Tactics and Technology in the Imperial Japanese Navy, 1887-1941". Naval Institute Press. ISBN 0-87021-192-7. .
  • Kennedy, Paul (1983). "The Rise and Fall of British Naval Mastery". Macmillan. ISBN 0-333-35094-4. .
  • Marriot, Leo (2005). "Treaty Cruisers: The First International Warship Building Competition". Pen & Sword. ISBN 1-84415-188-3. .
  • Potter, E, ed (1981). "Sea Power: A Naval History". Naval Institute Press. ISBN 0-87021-607-4. .
  • Jones, Howard (2001). "Crucible of power: a history of US foreign relations since 1897". Rowman & Littlefield. ISBN 0-8420-2918-4. .

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