George O'Brien
Cmdr. Robert 'Bob' Kingsley
Walter C. Kelly
Chief Mike 'Guns' Costello
Steve Pendleton
Ens. Richard 'Dick' Cabot (as Gaylord Pendleton)
Henry Victor
Baron Ernst von Steuben (U-boat commander)
Philip Ahlm
German Chief Petty Officer (uncredited)
Al Bennett
Naval Reservist (uncredited)
Earl Wayland Bowman
Naval Reservist/Swimmer and Diver (uncredited)
Bill Brande
Naval Reservist (uncredited)
William Collier Sr.
Mugs O'Flaherty (uncredited)
Leonard Davison
Naval Reservist (uncredited)
Joseph Depew
Naval Reservist (uncredited)
Francis Ford
Eric - Captain of Trawler (uncredited)
Robert Ford
Naval Reservist (uncredited)
Hans Fuerberg
Fritz Kampf (Second Officer of U-172) (uncredited)
Al Generaux
Naval Reservist (uncredited)
Bob Gillette
Naval Reservist (uncredited)
George Golden
Naval Reservist (uncredited)
Ben Hall
Elmer Harrigan (uncredited)
George Harris
Naval Reservist/Swimmer and Diver (uncredited)
Bob Kyle
Naval Reservist (uncredited)
Jack Martin
Naval Reservist (uncredited)
Harry Mount
Bugler on Gun Crew (uncredited)
Jack Murphy
Naval Reservist (uncredited)
Bob Nelson
Naval Reservist (uncredited)
Edward Peil Jr.
Naval Reservist (uncredited)
Nat Pendleton
'Butch' Wagner (uncredited)
Terrance Ray
'Skits' Reilly (uncredited)
Harry Schultz
German Officer (uncredited)
Ferdinand Schumann-Heink
Adolph Brucker (uncredited)
Robert Shepherd
Naval Reservist (uncredited)
Harry Strang
Gunner and drill sergeant (uncredited)
Anton Tell
German Chief Petty Officer (uncredited)
George Templeton
Naval Reservist (uncredited)
T.J.F. von Blankerburg
Naval Reservist/Swimmer and Diver (uncredited)
Frank Walton
Naval Reservist/Swimmer and Diver (uncredited)
Hans Winterhalder
German Chief Petty Officer (uncredited)
