Imperial Japanese Navy Aircraft Carriers 1921–45

The sides of Japanese carrier hangars were designed to vent the force of a bomb exploding on the hangar deck outwards instead of upwards, which could render the flight deck useless. In practice, the opposite frequently occurred, as the result of a bomb hit on the hangar deck was a ruptured flight deck. This design flaw was apparent throughout the war. Only the introduction of two late-war carriers with armored flight decks addressed this key vulnerability. This faulty hangar design was worsened by the fact that hangars were not flash or vapor tight. To ventilate the hangar, Japanese carriers used intake and exhaust fans. Fires on the hangar deck were an obvious danger that the Japanese planned to combat with a foam spray system using rows of pipes and nozzles on the hangar walls. In addition to the faulty hangar design, aviation fuel handling arrangements on Japanese carriers were dangerously inadequate. Fuel tanks were part of the structure of the ship, which meant that shocks to the hull were also absorbed by the tanks, creating possible leaks. Combined with the inability to vent these fumes from the hangar, the potential for disaster was obvious.