Once the flogging of Seaman Hommel (Peter Morton) was complete, vinegar was applied to the wound as an (unfortunately painful) antiseptic. If vinegar were not available salt could have been used instead, hence the saying "rubbing salt in the wound" whenever one trauma follows another.
Gregory Peck said that director Raoul Walsh was not interested in dialogue scenes. During talky sequences, Walsh sat down and read the newspaper.
Stanley Baker had been struggling to find acting work, but after he was cast as Mr. Harrison the boatswain shortly before his 22nd birthday, he was never out of work again. His most prominent role would be the lead character in Zulu (1964).
The ship Lieutenant William Bush (Robert Beatty) and Captain Horatio Hornblower (Gregory Peck) board to meet the Admiral at the end of the movie is the actual H.M.S. Victory, currently dry-docked at Portsmouth, England. As Admiral Horatio Nelson's flagship at Trafalgar, she is still commissioned to the present day as an official vessel of the Royal Navy, and the only surviving original ship of the line still in existence.
The film is based on the first three "Hornblower" novels: "The Happy Return" (a.k.a. "Beat to Quarters"), "Ship of the Line" and "Flying Colours". These were all written between 1937 and 1938.