FAQ for
The Final Countdown (1980) More at IMDbPro »

It's briefly discussed in the film but it deals with the paradox of time travel itself. How could they go back and prevent the attack on Pearl Harbor? Because if they had done that, then the attack never happened. If it had never happened they wouldn't have needed to try and stop it. Also rescuing Senator Chapman, they saved him from the fate of being strafed and killed by the Zeroes, however he wound up accidentally blowing himself up as a result. Therefore he never lived to be Roosevelt's running mate as he never made it passed that day alive. As far as everyone in 1941 was concerned, his yacht sank and he went missing and only those aboard the Nimitz knew what actually happened. Therefore even if one tries to alter history, the paradox of time travel prevents this from happening.

No, Japanese midget submarines also attacked Pearl Harbour and 3 were destroyed within it after attempting to torpedo 2 ships, succeeding in striking one of them. The Japanese Embassy in Washington was delivering a formal declaration of war to the US state department even as the attack was taking place. The Japanese also attacked US targets in The Phillipines, Wake Island and across Asia shortly after Pearl Harbour. US Navy ships were alreay firing on German U-boats in the Atlantic and 2 US destroyers had already been sunk in return