The London Naval treaty of 1930 regulated submarine warfare and extended the limitations on aircraft carriers designated in the Washington Treaty of 1922.

The numbers of capital ships (battleships and battlecruisers) allowed for the U.K., USA and Japan was set at 15-15-9.

The Japanese military felt angry and humiliated by the 5:5:3 naval ratio and Japan withdrew from the treaty in 1937.

Thereafter, Japan built aircraft carriers and battleships that were twice the tonnage of the largest British and American battleships.