As the Amethyst's main engines were no longer operational, HMS Magpie stood in for the shots of the ship moving.
HMS Amethyst sustained more damage during filming than during the actual battle.
HMS Amethyst was brought out of storage to participate in the film.
HMS Teazer stood in for both HMS Consort and HMS Concord.
In 1957, this film was distributed in the USA under the title "Battle Hell" on a double bill with Blood on the Moon starring Robert Mitchum and Barbara Bel Geddes.
The black-and-white feline seen aboard the Amethyst represents "Able Seacat" Simon, the ship's cat who became a celebrity after receiving the PDSA's Dickin Medal (at the behest of Lt. Cmdr. Kerans) for morale raising, despatching a rat infestation and surviving cannon shell injuries. The entire Amethyst crew attended his funeral in 1949 following his death of a viral infection caused by his war wounds.
The film debut of Bernard Cribbins.
The real HMS Amethyst was used at the start of filming. A special effects explosion was made too big and blew a hole in the hull, flooding the engine room. Amethyst was sent to the breakers and HMS Magpie was used for the rest of the film.
The real life Jack French (b. Teignmouth, Devon), the only telegraphist on board HMS Amethyst, died on May 4th 2011 at Cheltenham, Gloucestershire aged 84. During the highpoint of the siege, he stayed at his post for 6 days without sleep, kept awake through the aid of Benzedrine. Following the successful liberation of the ship he was awarded an immediate Distinguished Service Medal and ordered to take a complete rest. Having joined the Royal Navy aged 17 in 1942, French retired after 22 years service as a Chief Petty Officer. On his retirement from the navy, he took up a post at the Government Communications Headquarters (GCHQ) in Cheltenham.
The River Orwell, which runs between Felixstowe and Harwich, in Suffolk, England doubled as the Yangtze River during the making of this film.
The technical adviser was Commander John Simon Kerans, the British Naval Attaché "who commanded H.M.S. Amethyst during much of the period of the story, and whose exceptional help is gratefully acknowledged" as the credits put it; he is portrayed by Richard Todd. He had been awarded the DSO Distinguished Service Order ("for distinguished services during active operations against the enemy") for his part in the Amethyst incident, and soon after helping on the film served a term in the House of Commons after being elected Conservative Member of Parliament for The Hartlepools district from 1959 to 1964.