The previous war epic by Darryl F. Zanuck, The Longest Day (1962) was an extreme success. As stated by his son, producer Richard D. Zanuck, this was because it was about victory. He noted in contrast that Tora! Tora! Tora! is about defeat. Although the film made a great deal of money, it did nowhere near as well as The Longest Day. In Japan, however, the film was a smash. For the Japanese audience, it not only depicted a battle victory (after twenty-five years of films depicting defeat) but it also put the attack on more understandable footing; identifying not only the villains but also the motivation of those who believed that their actions were honorable.
The wounded sailor shown firing back at the strafing Japanese planes late in the film near the conclusion of the attack is based on Chief Ordnanceman John Finn, who was stationed at Kaneohe Naval Air Station on December 7, 1941. He set up a .50 caliber machine gun mount, and despite being wounded several times, fired back at strafing Zero fighters during the second attack wave, hitting several of them, and even shooting down one, piloted by combat unit leader Lieutenant Fusata Iida. Finn was later awarded the Medal of Honor for valor beyond the call of duty.
When Japanese characters refer to the date of the attack, they actually say "December 8." It's technically correct, as Japan is a day ahead of the U.S. It was translated as "December 7" in the subtitles to avoid confusing U.S. audiences.
Admiral Isoroku Yamamoto almost certainly did not utter his famous quotation about having "roused a sleeping giant and filled him with a terrible resolve." It seems to be a post-war invention based on Yamamoto's actual beliefs on the likely outcome of war with the U.S., and his affinity for the U.S. in general. It appears to be a more dramatic re-write of a letter he sent a month after the attack, in which he wrote, "A military man can scarcely pride himself on having 'smitten a sleeping enemy'. It is more a matter of shame, simply, for the one smitten. I would rather you made your appraisal after seeing what the enemy does, since it is certain that, angered and outraged, he will soon launch a determined counterattack." By contrast, his warning earlier in the film about attacking the U.S. that begins with, "If I am told to fight, I shall run wild for the first six months", is largely accurate.
Of all the time and money spent by Akira Kurosawa, less than one minute of the film he shot is in the final release version.