Backed by the Pentagon: The armed forces let the filmmakers do extensive location work and numerous large scale action sequences on active military bases, even allowing the producers to build a partial replica of the USS Nevada at Battleship Row. Some scenes even had real-life military personnel in bit parts and as extras.
Enforced Method Acting: A radio-controlled aircraft was supposed to roll down the runway past a bunch of extras, and then blow up. It went out of control and swerved toward the extras, who then really did start running for their lives.
Some sources claim one of the five B-17s used in the film actually had a landing gear failure so they rushed a film crew to the airfield to capture the emergency landing while the pilots circled to burn off fuel. Note that the footage of the actual one-wheel landing is lower quality than the rest of the film. Other sources state this is not true, however.
The famous scene of the P-40 veering out of control and plowing into the middle of a line of parked planes was an accident (it was supposed to just blow up). The stuntmen seen Outrunning the Fireball really are running for their lives.
Throw It In!: The B-17 crash-landing was a real accident during filming.
What Could Have Been: The movie was originally slated to be directed by British director David Lean (American side) and beloved Japanese auteur Akira Kurosawa (Japanese side), but Lean pulled out early in production. Kurosawa continued on for a while, until he was told that the Japanese section had been shortened to 90 minutes (the script Kurosawa had written was four hours long). Despite this, Kurosawa did begin production, but was replaced after three weeks. His experiences with Tora! Tora! Tora! and the failure of his next film Dodesukaden led to his Creator Breakdown in 1971.