Walter Pidgeon as Admiral Harriman Nelson

Robert Sterling as Captain Lee Crane

Barbara Eden as Lieutenant Cathy Conners

Peter Lorre as Comm. Lucius Emery

Joan Fontaine as Dr. Susan Hiller

Michael Ansara as Dr. Miguel Alvares

Frankie Avalon as Lieutenant Chip Romano

Regis Toomey as Dr. Jamieson

John Litel as Vice Admiral B.J. Crawford

Howard McNear as Congressman Llewellyn Parker

Henry Daniell as Dr. Zucco

Robert Easton as Sparks

Charles Tannen as CPO Mack Gleason

Mark Slade as Seaman Jimmy 'Red' Smith

Del Monroe as Seaman Kowski

Jonathan Gilmore as Seaman George Young

Anthony Monaco as Cookie

Skip Ward as Crew Member

Michael Ford as Crew Member

William Herrin as Crew Member (Uncredited)

Robert Buckingham as Crew Member (Uncredited)

Richard Adams as Crew Member (Uncredited)

Jimmy Murphy as Crew Member (Uncredited)

George Diestel as Lieutenant Hodges (Uncredited)

Larry Gray as Dr. Newmar (Uncredited)

David McLean as Ned Thompson (Uncredited)

Edward Rickard as Officer (Uncredited)

Charles Dierkop as Seaview Pilot (Uncredited)

Kendrick Huxham as UN Committee Chairman (Uncredited)

Art Baker as UN Commentator (Uncredited)

Rodger Terry as Guard (Uncredited)

Brad Brown as Guard (Uncredited)

Raoul Freeman as Delegate (Uncredited)

Al Bain as Delegate (Uncredited)

Harry Baum as Delegate (Uncredited)

Benjie Bancroft as Delegate (Uncredited)

Michael Cirillo as Delegate (Uncredited)

Harry Denny as Delegate (Uncredited)

John Giovanni as Delegate (Uncredited)

Bhupesh Guha as Delegate (Uncredited)

Esther Ying Lee as Delegate (Uncredited)

Robert Locke Lorraine as Delegate (Uncredited)

George Nardelli as Delegate (Uncredited)

Paul Power as Delegate (Uncredited)

Paul Ravel as Delegate (Uncredited)

Scott Seaton as Delegate (Uncredited)

Leslie Sketchley as Delegate (Uncredited)

Ray Spiker as Delegate (Uncredited)

Hal Taggart as Delegate (Uncredited)

Robert Strong as Delegate (Uncredited)

Ron Nyman as Crew Member (uncredited)