Joseph Cotten
— Admiral
Lloyd Haynes
— Lt. Dave Burston
Dewey Martin
— Skip Langley
Leonard Nimoy
— Comdr. Phil Kettenring
William Windom
— Capt. Frank Reardon
Keenan Wynn
— Orville Kelly
Malachi Throne
— Dr. Dykers
Sam Elliott
— Ens. William 'Bill' Sandover
Ivor Barry
— Donald Ellington
Ron Masak
— CPO Corky Schmidt
Gordon Hoban
— Second Karp (False Karp)
Lee Stanley
— Lt. Manners
David Thorpe
— Lt. Benson
Henry Olek
— Cab Driver
Dale Tarter
— Clarence W. "CW" Karp (First Karp)
James Beach
— Radar Operator
John Winston
— English Scientist
Larry McCormick
— Radio Operator
Paul Sears
— Paine
Ellen Tucker
— Mrs. Karp
Bill Keller
— Shore Patrolman
Bobby Herbeck
— Sonarman
Bo Johnson
— Seaman