Also Known As:
- X - The Unknown
- To teras apo ta vathi tis Gis
- X - den ukendte fare
- X - tuntematon
- X contro il centro atomico
- X, o Inimigo Desconhecido
- XX unbekannt
Directed by:
- Leslie Norman
Written by:
- Jimmy Sangster
Cast:
- Dean Jagger ... Dr. Adam Royston
- Edward Chapman ... John Elliott
- Leo McKern ... Insp. McGill
- Anthony Newley ... LCpl. 'Spider' Webb
- Jameson Clark ... Jack Harding
- William Lucas ... Peter Elliott
- Peter Hammond ... Lt. Bannerman
- Marianne Brauns ... Zena, the Nurse
- Ian MacNaughton ... Haggis (as Ian McNaughton)
- Michael Ripper ... Sgt. Harry Grimsdyke
- John Harvey ... Maj. Cartwright
- Edwin Richfield ... Soldier Burned on Back
- Jane Aird ... Vi Harding
- Norman Macowan ... Old Tom
- Neil Hallett ... Unwin (as Neil Hallet)
- Kenneth Cope ... Sapper Lansing
- Michael Brooke ... Willie Harding
- Frazer Hines ... Ian Osborn (as Fraser Hines)
- Max Brimmell ... Hospital Director
- Robert Bruce ... Dr. Kelly
- Angela Crow ... Bit Part
- Brown Derby ... Vicar
- Raymond Dudley ... Bit Part
- Archie Duncan ... Sgt. Yeardye
- Lawrence James ... Gerard
- Edward Judd ... 2nd Soldier
- Stella Kemball ... Willie's Room Nurse
- Jack Lambert ...
- Stevenson Lang ... Reporter
- Philip Levene ... Security Man
- Brian Peck ... 1st Soldier
- Anthony Sagar ... Gateman
- Barry Steele ... Soldier in Trench
- John Stirling ... Police Car Driver
- John Stone ... Jerry
- French Taylor ... PC Williams
- Shaw Taylor ... Police Radio Operator
- Neil Wilson ... Russell
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