The London Naval Treaty

On 22 April 1930, in London, representatives of Great Britain and its dominions, the United States, Japan, France and Italy signed the Treaty for the Limitation and Reduction of Naval Armament, known as the London Naval Treaty. It was a sequel to the Washington Naval Treaty of 1922. It extended the ban on building new battleships until the end of 1936, required several of them to be scrapped, for the first time capped the total tonnage of cruisers, destroyers and submarines, and laid down that submarines must observe the same rules of the law of war towards merchant ships as surface warships. The common statement that five powers agreed to limit their shipbuilding needs qualifying, however. All five signed the general parts, but only the three largest navies – the American, British and Japanese – accepted the tonnage limits. France and Italy, at odds over which of them should have the stronger fleet in the Mediterranean, signed the treaty without its most important part. In Japan the treaty provoked a crisis that weakened the government’s control over the armed forces for years to come and became one of the turning points on the road to war.

The cruiser race

The Washington treaty had limited battleships and aircraft carriers but left cruisers, destroyers and submarines without numerical limits. It stipulated only that a cruiser could displace no more than 10,000 tons and carry guns no larger than 8 inches (203 mm). That ceiling quickly became a target. In the 1920s Japan, Britain, France, Italy and the United States built so-called treaty cruisers, as large and as heavily armed as the treaty allowed. Japan’s Myōkō-class cruisers were regarded as the most powerful in the world, and its Fubuki-class destroyers outclassed every other ship of their type.

In 1927 President Calvin Coolidge called a conference in Geneva to limit these classes of warship as well. It ended in failure. The British, who had to protect the trade routes of an entire empire, wanted many smaller cruisers; the Americans, short of bases in the Pacific, wanted a few large ones. The admirals on both sides could not agree, and Anglo-American relations soured for several years. The breakthrough came only with a change of governments. In 1929 Herbert Hoover became president, and in London Ramsay MacDonald formed the second Labour government. Both men wanted an agreement, not least because their countries had just signed the Kellogg–Briand Pact renouncing war. In October 1929 MacDonald became the first serving British prime minister to visit the United States, and he held talks with Hoover at the president’s country retreat on the Rapidan River in Virginia. They agreed on the principle of parity between their two fleets in every class of warship, and in early October the British government invited the other naval powers to London. A few weeks later the Wall Street Crash gave every government yet another reason to save money on armaments.

The conference

The conference was opened on 21 January 1930 by King George V, whose speech was broadcast on the radio. This time, having learnt the lesson of Geneva, the delegations were led by politicians rather than admirals. MacDonald himself headed the British delegation, Secretary of State Henry Stimson the American, Prime Minister André Tardieu and Foreign Minister Aristide Briand the French, and Dino Grandi, foreign minister in Benito Mussolini’s government, the Italian. The Japanese delegation was led by the former prime minister Reijirō Wakatsuki, accompanied by the Navy Minister, Admiral Takeshi Takarabe, and the ambassador in London, Tsuneo Matsudaira.

The Japanese government of Prime Minister Osachi Hamaguchi of the Minseitō party was pursuing a policy of retrenchment. In January 1930 it had returned the yen to the gold standard and needed the confidence of foreign bankers. The Foreign Minister, Kijūrō Shidehara, was the leading advocate of cooperation with America and Britain. Nevertheless, the delegation brought to London three demands agreed with the navy: 70 per cent of American tonnage in all auxiliary vessels, 70 per cent in heavy cruisers, and 78,000 tons of submarines – roughly what Japan already possessed. The Navy General Staff regarded these figures as the minimum that would allow the Japanese fleet to defend itself against the American one in home waters.

France demanded a large tonnage, citing its extensive colonial empire and the need for security against Germany, and refused Italy parity. Mussolini wanted an Italian fleet equal to the French one. The dispute was insoluble, and the five-power talks soon turned into three-power talks. In mid-March Senator David Reed of the American delegation and Ambassador Matsudaira worked out a compromise. Japan was to receive 69.75 per cent of United States tonnage in auxiliary vessels overall, parity in submarines but at a lower level than it had demanded, and only about 60 per cent in heavy cruisers. The Americans agreed, however, to delay building their last three heavy cruisers so that, for as long as the treaty remained in force, Japan would in practice keep a ratio close to 70 per cent.

What the treaty laid down

The treaty signed on 22 April 1930 had five parts. Part I extended the holiday in battleship construction until 31 December 1936, except for two ships that France and Italy had earlier been allowed to build. Britain was to withdraw five battleships and battlecruisers, the United States three and Japan one – the battlecruiser Hiei, which was partly disarmed and converted into a training ship. After these reductions the ratio of capital ships among the three powers stood at 15:15:9. The treaty also closed the loophole concerning aircraft carriers of under 10,000 tons, which had not previously counted towards the limits.

Part III, accepted only by the United States, the British Empire and Japan, set limits that were to remain in force until the end of 1936. For the first time the treaty distinguished between cruisers with guns above 155 mm (heavy) and those with guns of up to 155 mm (light). For heavy cruisers the United States was allotted 180,000 tons, or 18 ships, Britain 146,800 tons (15 ships) and Japan 108,400 tons (12 ships). For light cruisers Britain received 192,200 tons, the United States 143,500 and Japan 100,450. For destroyers, none of which could exceed 1,850 tons, the Americans and the British were given 150,000 tons each and Japan 105,500. For submarines all three states received 52,700 tons each, and no single submarine could exceed 2,000 tons, apart from three larger boats for each country. Article 21, the so-called escalator clause, allowed any of the three powers to exceed the limits if it felt threatened by the naval build-up of a third state. France and Italy were chiefly in mind.

Part IV proved the most enduring. Its Article 22 laid down that submarines acting against merchant ships must observe the same rules of international law as surface warships. They could not sink a ship that offered no resistance without first securing the safety of its passengers, crew and ship’s papers, and lifeboats were not regarded as a place of safety unless, given the sea and weather conditions, the people in them had a chance of reaching land or another vessel. The memory of the unrestricted submarine warfare of 1915–1918 was still fresh. Unlike the rest of the treaty, this part had no expiry date.

Ratification and crisis in Tokyo

In Britain and the United States the treaty was criticised by admirals and big-navy advocates, but ratification was never in doubt. The US Senate approved it in July 1930 at a special session. On 27 October 1930 the instruments of ratification of the three principal signatories were deposited in London and the treaty came into force.

In Japan a storm broke. The Navy General Staff, headed by Admiral Kanji Katō – the same man who had protested in Washington in 1922 – judged the compromise unacceptable because it gave neither 70 per cent in heavy cruisers nor the submarine tonnage demanded. The Navy Ministry and the fleet command were inclined to accept it. Hamaguchi, convinced that failure to agree would mean an arms race Japan could not win, cabled the delegation on 1 April instructing it to accept. The chief of staff had earlier tried to put his case directly to Emperor Hirohito, but his audience was postponed. The right-wing press later accused the Grand Chamberlain, Kantarō Suzuki, and the Lord Keeper of the Privy Seal, Nobuaki Makino, of deliberately keeping the admiral away from the monarch.

The opposition Rikken Seiyūkai, led by Tsuyoshi Inukai and Ichirō Hatoyama, attacked the government in parliament in a way that would later rebound on the party itself. It charged that by signing the treaty against the wishes of the General Staff, the government had infringed the prerogative of supreme command, which under the Meiji Constitution belonged to the emperor and which the General Staff could exercise without going through the government. The government replied that the size of the armed forces was a matter for the cabinet, which was answerable to the emperor for state policy. The dispute over the so-called infringement of the prerogative of supreme command (tōsuiken kanpan) undermined the principle that the civilian authorities had the final say on the budget and foreign policy. In May a junior naval officer, Lieutenant Commander Eiji Kusakari, killed himself in protest. In June Kanji Katō tendered his resignation directly to the emperor. The aged Admiral Heihachirō Tōgō, the victor of Tsushima, also came out against the treaty.

Hamaguchi, backed by the emperor and by the last of the genrō, Prince Kinmochi Saionji, did not give way. The resistance of the Privy Council, which had to give its opinion on the treaty, weakened when the government let it be known that it could change the council’s membership. On 1 October 1930 the council approved the treaty unanimously, and on 2 October the emperor ratified it. The government had won, but it paid a price. On 14 November 1930, at Tokyo Station, Tomeo Sagoya, a young member of the nationalist organisation Aikokusha, shot the prime minister in the abdomen. Hamaguchi survived the attack but never recovered his health. He resigned in April 1931 and died on 26 August 1931.

The long shadow of London

The London Naval Treaty was the last successful disarmament agreement between the great powers before the Second World War. Its consequences in Japan, however, proved more important than its tonnage limits. The crisis of 1930 deepened the split in the navy between the Treaty Faction and the Fleet Faction, and taught the military that a government which concluded agreements against the wishes of the general staffs could be accused of infringing the emperor’s prerogatives. The politicians themselves soon learnt this lesson. In September 1931 the Kwantung Army, without the government’s consent, staged the Mukden incident and seized Manchuria. On 15 May 1932 young naval officers, among whom hatred of the “London treaty” ran high, murdered Prime Minister Inukai – the same man who two years earlier had turned the argument about the prerogative of command against Hamaguchi. It marked the end of party government in pre-war Japan. In 1933–1934 the Navy Minister, Mineo Ōsumi, with the support of Tōgō and the chief of staff, Prince Hiroyasu Fushimi, purged many Treaty Faction admirals from the navy.

On 29 December 1934 Japan renounced the Washington treaty. It came to the second London conference, which opened in December 1935, demanding parity with the United States and Britain, and on 15 January 1936, when this was refused, it walked out. The Second London Naval Treaty of 25 March 1936 was signed only by the United States, Britain and France. At the end of 1936 the quantitative limits of both treaties expired and an open naval arms race began. Japan secretly built the Yamato-class battleships, while the United States – where since 1933 President Franklin Delano Roosevelt had been channelling Depression-relief funds into the shipyards – expanded its fleet on an unprecedented scale. In Europe the limits had lost their meaning even earlier: in June 1935 Britain concluded a naval agreement with Hitler that allowed Germany a fleet equal to 35 per cent of the British one, breaking the naval provisions of the Treaty of Versailles.

Only the rules on submarine warfare in Article 22 survived. In November 1936 they were restated in a separate London Protocol, to which Germany, Italy, Japan and the Soviet Union, among others, acceded. During the Second World War no one observed them. German U-boats sank ships without warning from the first months of the war, and on 7 December 1941, the day of the attack on Pearl Harbor, the United States ordered unrestricted submarine warfare against Japan. When the International Military Tribunal at Nuremberg tried Admiral Karl Dönitz in 1946, it found that the German navy had violated the 1936 protocol but imposed no sentence on him for it, because the British and Americans had acted in a similar way. A treaty that in 1930 was meant to protect merchant shipping and secure peace at sea had become, ten years later, yet another written commitment swept away by war.