The Silent Enemy

It is World War Two, and newly appointed bomb disposal lieutanant Lionel 'Buster' Crabb (Laurence Harvey) joins the British naval fleet at Gibraltar just as two battleships are destroyed by enemy frogmen off Alexandria. Crabb sets about forming an Underwater Working Party to battle the mini submarines whcih are threatening Allied shipping, and soon forms the suspicion that the forgmmen are working out of neutral Spain. When he is refused permission to go after them, Crabb decides to disobey orders and launches his own commando raid.