EnglishHugh Marlowe as Dr Russell A Marvin
Joan Taylor as Carol Marvin
Donald Curtis as Maj Huglin Liason Officer
Morris Ankrum as Brig Gen John Hanley
John Zaremba as Prof Kanter
Thomas Browne Henry as Vice Adm Enright
Grandon Rhodes as Gen Edmunds
Larry J Blake as Motorcycle Cop
Fred Aldrich as Airplane Passenger/Officer in Sighting Montage/Man
Holly Bane as Bit Role (unconfirmed)
Nicky Blair as Military Officer at Experiment
Charles Evans as Dr Alberts
Paul Frees as Narrator/Alien Voice
Duke Green as Bit Role
Clark Howat as Sgt Nash
Harry Lauter as Cutting Generator technician
Don Marlowe as Bit Role (unconfirmed)
Forbes Murray as Military Officer at Experiment
Alan Reynolds as Maj Kimberly
Bert Stevens as Officer in UFO Sighting Montage
Arthur Tovey as Officer/Civilian at Military Conference
Dale Van Sickel as Crushed Beneath Wall
Frank Wilcox as Alfred Cassidy
Beal Wong as Radio Listener in China
William Woodson as Off-Screen Narrator (unconfirmed)