Directed by William Fairchild Screenplay by William Fairchild 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 Foà 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