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Dr. Russell A. Marvin
Joan Taylor
Carol Marvin
Donald Curtis
Maj. Huglin
Morris Ankrum
Brig. Gen. John Hanley
Thomas Browne Henry
Vice Adm. Enright
Grandon Rhodes
Gen. Edmunds
John Zaremba
Prof. Kanter
Paul Frees
Alien (voice)
Frank Wilcox
Alfred Cassidy
Sydney Mason
Frank the garage man
Larry J. Blake
Motorcycle cop
Bert Stevens
Air Intelligence Command Officer
Forbes Murray
Military Officer at Experiment
Arthur Tovey
Officer/Civilian at Military Conference
Alan Wells
Major Kimberly
Nicky Blair
Military Officer at Experiment (uncredited)
Jimmy Cross
Military Messenger (uncredited)
Jack Deery
Military Officer (uncredited)
Charles Evans
Dr. Alberts (uncredited)
Raoul Freeman
Military Official (uncredited)
Paul Frees
Alien (voice) (uncredited)