Set in the Mediterranean in 1941, the Italians begin using underwater chariots to mine the undersides of Allied ships. Explosives expert Lionel Crabbe arrives in Gibraltar to organize defenses, but finds only two British divers available to assist him. Even more concerning, it becomes likely that the Italians are secretly using neutral Spain across the bay as their primary base of operations. Cast: - Laurence Harvey as Lieutenant Lionel Crabb, R.N.V.R. - Dawn Addams as Third Officer Jill Masters, W.R.N.S. - Michael Craig as Leading Seaman Knowles - John Clements as the Admiral - Sid James as Chief Petty Officer Thorpe - Alec McCowen as Able Seaman Morgan - Nigel Stock as Able Seaman Fraser - Ian Whittaker as Ordinary Seaman Thomas - Arnoldo Foé as Tomolino - Gianna Maria Canale as Conchita - Massimo Serato as Forzellini - Giacomo Rossi-Stuart as Rosati - Carlo Giustini as Fellini - Raymond Young as Celloni - David Lodge as Sergeant - Ewen Solon as Willowdale Captain - Brian Oulton as Holford - Howard Marion-Crawford as Wing Commander - Cyril Shaps as Miguel - Lee Montague as Miguel's Mate - John Lee as Flag Lieutenant - Terence Longdon as Lieutenant Bailey - Ian MacNaughton as Sentry outside Admiral's Office - David Fotheringham as Italian frogman - Alan Webb as British Consul - John Moffatt as Diving Volunteer - Harold Siddons as Army Interrogation Officer - Michael Brill as Naval Interrogation Officer Runtime: 112 minutes.