Second London Naval Treaty
Another factor was the "escalator clause" of the Second London Naval Treaty, which reverted the gun caliber limit from to . Japan had refused to sign the treaty and in particular refused to accept the 14-inch gun caliber limit or the 5:5:3 ratio of warship tonnage limits for Britain, United States, and Japan respectively. This resulted in the three treaty powers, the United States, Britain, and France, invoking the escalator clause after April 1937. Circulation of intelligence evidence in November 1937 of Japanese capital ships violating naval treaties caused the treaty powers to expand the escalator clause in June 1938, which amended the standard displacement limit of battleships from to .