The "Tiger Shark" teeth and eyes painted on the noses of the planes were there for psychological reasons. It was believed that the Japanese, coming from a seafaring nation, would be frightened of being attacked by sharks. There is no word on whether it had any effect.
Some clips of the dogfights and Japanese ack-ack guns were from confiscated Japanese newsreels.
The opening scene shows a Japanese air raid and in the aftermath a crying child is sitting alone amid debris. This scene virtually duplicates a famous photo taken in 1937 and published in Life magazine following a Japanese air raid on Shanghai. (Located in the National Archives, ARC Identifier: 535557)
John Wayne's character's nickname of Pappy was an actual nickname of a member of the AVG. Greg "Pappy" Boyington flew with the AVG early on but went back to the Marine Corps later in the war. He would gain fame flying with the "Black Sheep" Squadron flying from Guadalcanal.
The Flying Tigers' planes were full-size mock-ups made mostly of plywood and balsa wood, not - as has often been thought - real aircraft. The "engine" noises were sound effects added after production.