sentences:  In the film, a single horn blast was given every fifteen minutes, and Sunderstrom is ordered to return immediately after hearing the third blast.In the novel, the submarine crew gives one horn blast for a quarter of an hour, two for half an hour, three for three quarters, and four for a whole hour.He's ordered to stop what he's doing at five horn blasts (1 1/4 hours) and return at six horn blasts (1 1/2 hours).