In keeping with the original Nazis-as-villains idea, the hero originally saw Adolf Hitler himself standing on the balcony of the villain's lair. He disappeared when the extensive re-shooting was done. Hitler was played once again by Bobby Watson.
This film was originally shot with the bad guys conducting the germ warfare experiments as Nazis (which is why many of the characters have German names). However, producer Howard Hughes had a change of heart and decided that Communists were more of a menace than crazed Nazi scientists (it was also the height of the McCarthy "Red Scare" era) and ordered extensive re-shooting, with the villains now becoming former Nazis but current Communists.