In the waning days of WWI, a U.S. "Mystery Ship," sets sail for the coast of Spain towing a submarine. Their mission is to find and sink a U-boat that has been especially effective in attacking Allied shipping. Posing as a harmless schooner, the mystery ship is in fact fitted with a formidable gun capable of sinking a U-boat. Stopping in the Canary Islands to refuel, the crew interacts with locals involved with Germans, and with Germans themselves, including the sister of the U-Boat commander, who is lurking offshore waiting for the coming battle.
as Cmdr. Robert 'Bob' Kingsley
as Anna Marie Von Steuben
as Fraulein Lolita
as Chief Mike 'Guns' Costello
as 'Lug' Kaufman
as Ens. Richard 'Dick' Cabot (as Gaylord Pendleton)
as Chief Joe Cobb
as Lt. 'Mac' McGregor
as Baron Ernst von Steuben (U-boat commander)
as Franz Shiller
as German Chief Petty Officer (uncredited)
as Naval Reservist (uncredited)
as Naval Reservist/Swimmer and Diver (uncredited)
as Naval Reservist (uncredited)
as Mugs O'Flaherty (uncredited)
as Naval Reservist (uncredited)
as Naval Reservist (uncredited)
as Eric - Captain of Trawler (uncredited)
as Naval Reservist (uncredited)
as Fritz Kampf (Second Officer of U-172) (uncredited)
as Hoffman (uncredited)
as Naval Reservist (uncredited)
as Naval Reservist (uncredited)
as Naval Reservist (uncredited)
as Elmer Harrigan (uncredited)
as Naval Reservist/Swimmer and Diver (uncredited)
as Naval Reservist (uncredited)
as Naval Reservist (uncredited)
as Bugler on Gun Crew (uncredited)
as Naval Reservist (uncredited)
as Merkel (uncredited)
as Naval Reservist (uncredited)
as Naval Reservist (uncredited)
as 'Butch' Wagner (uncredited)
as 'Skits' Reilly (uncredited)
as Gunner (uncredited)
as German Officer (uncredited)
as Adolph Brucker (uncredited)
as Naval Reservist (uncredited)
as Gunner and drill sergeant (uncredited)
as German Chief Petty Officer (uncredited)
as Naval Reservist (uncredited)
as Winkler (uncredited)
as Naval Reservist/Swimmer and Diver (uncredited)
as Naval Reservist/Swimmer and Diver (uncredited)
as Levinsky (uncredited)
as German Chief Petty Officer (uncredited)
