In World War II, Royal Marine Major Stringer (José Ferrer) and Captain Thompson (Trevor Howard) chose volunteers for an unknown job. They trained the volunteers intensively in top secrecy for more than a year and then embarked with them on the most dangerous mission of the war - the canoe invasion of an enemy-held French port for the purpose of blowing up giant battleships. The ten "canoe commandoes" were carried to their jump-off point by submarine, despite a depth-charge attack. Facing fantastic hazards, they paddled 70 miles through enemy waters to complete their mission. But only two survivors would return!