William Hopper
Colonel Robert Calder
Joan Taylor
Marisa Leonardo
Frank Puglia
Dr. Leonardo
John Zaremba
Dr. Judson
Thomas Browne Henry
Maj. Gen. A.D. McIntosh
Tito Vuolo
Commissario Unte
Jan Arvan
Signore Contino - Government Official
Arthur Space
Dr. Sharman
Bart Braverman
Pepe
Don Orlando
Fisherman Mondello (uncredited)
George Khoury
Fisherman Verrico (uncredited)
Darlene Fields
Reporter Reynolds (uncredited)
George Pelling
Reporter Maples (uncredited)
James Dime
Felix Roi, a French reporter (uncredited)
Sid Cassel
Farmer (uncredited)
Ray Harryhausen
Man Feeding Elephant (uncredited)
Noel Drayton
1st Reuters News Correspondent (uncredited)
Rollin Moriyama
Dr. Koruku - Japanese Scientist