Claim: Japan's Shinano, an aircraft carrier built by the Imperial Japanese Navy (IJN) during World War II, had the thickest hangar deck (7.5 in) among some of the World War II era aircraft carriers.
Evidence: Shinano (信濃) was an aircraft carrier built by the Imperial Japanese Navy (IJN) during World War II, the largest such built up to that time. Designed to resist penetration by 500-kilogram (1,100 lb) bombs dropped by a dive bomber, the flight deck consisted of 75 millimeters (3 in) of armor plate laid over 20 millimeters (0.8 in) of ordinary steel.