Gene Evans as Steve Karnes

André Morell as Prof. James Bickford

Leigh Madison as Jean Trevethan

John Turner as John

Alastair Hunter as Dr. C. A. Morris, the village doctor

Lloyd Lamble as Senior Admiral, at the Admiralty

Jack MacGowran as Dr. Sampson, the paleontologist

Maurice Kaufmann as Mini Submarine Officer

Henri Vidon as Tom Trevethan

Patrick Jordan as Photo Lab Aide

Howard Lang as Naval Commader, at the "Valkyrie" wreck (uncredited)

Leonard Sachs as Dialogue Scientist at Conference (bit)

Ernest Blyth as Scientist at Conference (uncredited)

Neal Arden as TV Newscaster (uncredited)

Paul Beradi as Man Listening to Car Radio (uncredited)

Max Faulkner as PLA Radio Operator (uncredited)

Neil Hallett as Dr. Sampson's Helicopter Pilot (uncredited)

André Maranne as French Radio Officer (uncredited)

Derren Nesbitt as The Radar Operator, at the radar room (uncredited)

Guy Standeven as Naval Officer in Situation Room (uncredited)