cast
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George O'Brien
Cmdr. Robert 'Bob' Kingsley
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Marion Lessing
Anna Marie Von Steuben
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Mona Maris
Fraulein Lolita
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Walter C. Kelly
Chief Mike 'Guns' Costello
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Warren Hymer
'Lug' Kaufman
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Steve Pendleton
Ens. Richard 'Dick' Cabot (as Gaylord Pendleton)
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Walter McGrail
Chief Joe Cobb
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Larry Kent
Lt. 'Mac' McGregor
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Henry Victor
Baron Ernst von Steuben (U-boat commander)
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John Loder
Franz Shiller
- 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)
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William Collier Sr.
Mugs O'Flaherty (uncredited)
- Leonard Davison Naval Reservist (uncredited)
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Joseph Depew
Naval Reservist (uncredited)
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Francis Ford
Eric - Captain of Trawler (uncredited)
- Robert Ford Naval Reservist (uncredited)
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Hans Fuerberg
Fritz Kampf (Second Officer of U-172) (uncredited)
- Curt Furberg Hoffman (uncredited)
- Al Generaux Naval Reservist (uncredited)
- Bob Gillette Naval Reservist (uncredited)
- George Golden Naval Reservist (uncredited)
- Ben Hall Elmer Harrigan (uncredited)
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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)
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Jack Murphy
Naval Reservist (uncredited)
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Maurice Murphy
Merkel (uncredited)
- Bob Nelson Naval Reservist (uncredited)
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Edward Peil Jr.
Naval Reservist (uncredited)
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Nat Pendleton
'Butch' Wagner (uncredited)
- Terrance Ray 'Skits' Reilly (uncredited)
- Marvin Schecter Gunner (uncredited)
- Harry Schultz German Officer (uncredited)
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Ferdinand Schumann-Heink
Adolph Brucker (uncredited)
- Robert Shepherd Naval Reservist (uncredited)
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Harry Strang
Gunner and drill sergeant (uncredited)
- Anton Tell German Chief Petty Officer (uncredited)
- George Templeton Naval Reservist (uncredited)
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Harry Tenbrook
Winkler (uncredited)
- T.J.F. von Blankerburg Naval Reservist/Swimmer and Diver (uncredited)
- Frank Walton Naval Reservist/Swimmer and Diver (uncredited)
- Harry Weil Levinsky (uncredited)
- Hans Winterhalder German Chief Petty Officer (uncredited)