Fantastic Voyage

Fantastic Voyage is a 1966 science fiction film written by Harry Kleiner, based on a story by Otto Klement and Jerome Bixby. The film is about a submarine crew who shrink to microscopic size and venture into the body of an injured scientist to repair the damage to his brain. The original story took place in the 19th century and was meant to be a Jules Vernestyle adventure with a sense of wonder. Kleiner abandoned all but the concept of miniaturization and added a Cold War element. It was directed by Richard Fleischer, and starred Stephen Boyd, Raquel Welch, Edmond OBrien and Donald Pleasence. It was 20th CenturyFoxs final film to use the CinemaScope process.

The United States and the Soviet Union have both developed technology that can miniaturize matter by shrinking individual atoms, but only for a limited amount of time, depending on how small the item is miniaturized.The scientist Dr. Jan Benes, working behind the Iron Curtain, has figured out how to make the process work indefinitely. With the help of the CIA, he escapes to the West, but an attempted assassination leaves him comatose with a blood clot in his brain. ........

Source: Wikipedia