Greyhound is based on a novel written by C.S.Forester and the title of the book is The Good Shepherd.
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Here is the goodreads synopsis of The Good Shepherd:
C.S. Forester's name on a novel gives promise of excellent entertainment, but always something more--the development of character, the flow of history, and the stress of events. THE GOOD SHEPHERD is in this genre.A convoy is ploughing through icy, submarine-infested North Atlantic seas during the most critical days of WW II. In charge is Commander George Krause, an untested veteran of the U.S. navy. He faces 48 hours of desperate peril.