Trivia: During the scenes dealing with the dive bomber attacks on the RAF radar stations, the filmmakers used rather un-convincing radio-controlled models to portray the German Ju87 Stukas. Originally, the producers had intended to use Proctor trainers, modified to resemble the Stuka. However the British aviation authorities refused to pass them as airworthy, forcing the producers to resort to using the models.
Trivia: During the attack by Heinkels from Norway across the North Sea English Squadron Leader says "help yourself everybody, there's no fighter escort." In reality the Heinkels had an escort of twin engine Me 110s. In 1968 there were no airworthy Me 110s so the movie ignored them.