An actual ship was sunk for the production, which was filmed in part at sea.
Three United States Navy ships were used in the movie: the submarine cruiser Argonaut, the destroyer Preble, and the Noa.
U boats were in fact a significant danger in WWI and every allied merchant fleet suffered serious loss of both ships and men . The Atlantic Convoy System with escort vessels was invented during the Great War, to help counter the threat.
An unscheduled rescue at sea was performed by the actors during production when a launch exploded off the Coronado Islands in the Pacific Ocean. Nine men, members of the film expedition, were in the launch when it's gas tanks blew up, throwing all into the water. Second cameraman Bobby Burns and sound engineer Elmer Ellsworth were slightly burned. William Boyd, James Gleason, Robert Armstrong and the director Al Rogell plunged into the ocean to rescue their assistants.
The United States Navy ordered submarine crews docked at San Pedro, California, USA to cooperate and participate in the filming of this movie. Three divisions of the Navy worked with the production, which also employed thousands of extras.