The were two battleships of the Imperial Japanese Navy (IJN), and , laid down leading up to World War II and completed as designed. A third hull laid down in 1940 was converted to an aircraft carrier, , during construction. Displacing nearly at full load, the completed battleships were the heaviest ever constructed. The class carried the largest naval artillery ever fitted to a warship, nine 460-mm (18.1 in) naval guns, each capable of firing shells over . Due to the threat of U.S. submarines and aircraft carriers, both Yamato and Musashi spent the majority of their careers in naval bases at Brunei, Truk, and Kure—deploying on several occasions in response to U.S. raids on Japanese bases. All three ships were sunk by the U.S. Navy; Musashi while participating in the Battle of Leyte Gulf in October 1944, the Shinano while under way from Yokosuka to Kure for fitting out in November 1944, and the Yamato while en route from Japan to Okinawa as part of Operation Ten-Go in April 1945. Background The design of the Yamato-class battleships was shaped by expansionist movements within the Japanese government, Japanese industrial power, and the need for a fleet powerful enough to intimidate likely adversaries. Most importantly, the latter, in the form of the Kantai Kessen (“Decisive Battle Doctrine”), a naval strategy adopted by the Imperial Japanese Navy prior to the Second World War, in which the Japanese navy would win a war by fighting and winning a single, decisive naval action. After the end of the First World War, many navies—including those of the United States, the United Kingdom, and Imperial Japan—continued and expanded construction programs that had begun during the conflict. The enormous costs associated with these programs pressured their government leaders to begin a disarmament conference. On 8 July 1921, the United States' Secretary of State Charles Evans Hughes invited delegations from the other major maritime powers—France, Italy, Japan, and the United Kingdom—to come to Washington, D.C. and discuss a possible end to the naval arms race. The subsequent Washington Naval Conference resulted in the Washington Naval Treaty. Along with many other provisions, it limited all future battleships to a standard displacement of and a maximum gun caliber of . It also agreed that the five countries would not construct more capital ships for ten years and would not replace any ship that survived the treaty until it was at