Japan and Britain. It was decided in negotiations that a ratio of power would be established of 5:5:3, corresponding to America, Britain and Japan in that order. This meant that the Japanese fleet would only be allowed a fraction of the power that was given to the American and British fleets, a fact which lead directly to the Japanese construction of super battleships. Although this treaty was extremely explicit in its governance of battleship and cruiser tonnage, it was lax in the area of carriers, a fact which all of the participants failed to take advantage of. The growing tensions of the 1930s and the rise of aggressive nationalist governments in Japan, Italy and Germany restarted the building programs, with even larger ships than before; Yamato, the largest battleship ever, displaced 72,000 tons, and mounted 18.1-inch guns. Emergence of the aircraft carrier Shortly after the end of the war, the first aircraft carriers designed from the keel up were completed: the Japanese Hōshō and the British Hermes. Both ships were too small to be satisfactory. Under the terms of the Washington Treaty, Britain, America and Japan were allowed to convert two ships that were due to scrap under the treaty into aircraft carriers. By luck as much as planning, the Americans and Japanese both developed large carriers that were capable of handling up to 90 aircraft, based on the hulls of battlecruisers due to be scrapped under the Washington Treaty. Both navies gradually began to develop new tactics for employing aircraft carriers in battle, although these tactics did not come into full fruition until the middle of the Pacific Campaign of WWII. Development of new weapons The Magnetic mine was a German development that allowed naval mines to become more deadly than ever; by detecting the magnetic charge of a large ship a mine could detonate without ever having to make contact with the craft, and it would be completely harmless to smaller ships, whose lack of a strong magnetic field allowed them to pass safely, saving the mine for more valuable targets. The oxygen Long lance torpedo, which used pure oxygen instead of air for the oxidizer, was developed by the Japanese just prior to their full involvement in WWII. Despite having more than twice the effective range of the best Allied torpedoes and lacking the tell-tale torpedo wake, the oxygen torpedo was not used to its fullest capacity