In the immediate postwar period, the innovations of the late war U-boats were quickly adopted by the major navies. Both the United Kingdom and The United States studied the German Type XXI and used the information to modify WW2 fleet boats, the US with the GUPPY program and the UK with the Overseas Patrol Submarines Project. The Soviets launched new submarines patterned on Type XXIs, the Whiskey and Zulu classes. Britain also tested hydrogen peroxide fuels in "Meteorite", "Excalibur", and "Explorer", with less success.