This movie was the sixth most popular movie at the British box-office in 1955.

In the scene where Lieutenant Tom Corbett (Donald Sinden) and his crew first board the midget submarine, the view of three Castle-class frigates tied alongside each other can be clearly seen in the background, this view of the three frigates was also seen in "The Cruel Sea (1953)," when Ericson and Lockhart first take charge of the factitious H.M.S. Saltash Castle after they survive the sinking of their first ship H.M.S. Compass Rose.

The success of this movie caused Sir John Mills to be voted the most popular movie star in the U.K. that year.

The watch on Commander Fraser's (Sir John Mills') wrist is the famous Jaeger-LeCoultre Reverso, a watch with a case that can be turned around so that the front faces downwards, thus protecting the glass from hard knocks. This robust watch is nowadays considered as an ultra-luxury item.

When this movie was made in 1954, Queen Elizabeth II was on the throne, but throughout the war, it was her father, King George VI, who was the monarch. Whether by design or chance, most of the cast have historically accurate cap badges, which is to say they include a King's crown. The notable exception is Sir John Mills, whose cap badge has a Queen's crown.

Original military equipment from World War II was accessed and used for the making of this movie.

Operation Source, the real life mission on which this film was based, was actually considered a failure in many respects. The Germans easily repaired the damage to Tirpitz. Historians William Garzke and Robert Dulin remarked that the successful repair effort was "one of the most notable feats of naval engineering during the Second World War."

An original member of the mini-sub operations, Commander Donald Cameron, who had been a Lieutenant at the time of the mission, acted as a Consultant and Adviser for the production.

The attack by midget submarines did considerable damage, and actually put the Tirpitz out of action, although the damage was easily repaired. The Tirpitz was later sunk using gigantic six-ton bombs by R.A.F. Squadron 617 in November 1944.

The central event of this movie is the X-craft attack on the battleship Tirpitz. The Captain of X-craft 5 was Henty Henty-Creer. Before World War II, Henty Henty-Creer was a movie cameraman and worked on "49th Parallel (1941)," "The Thief of Bagdad (1940)," and "The Four Feathers (1939)."

This movie was based on the actual Chariot human torpedo attacks on the German battleship Tirpitz during World War II, as well as Operation Source, which was a series of attacks by X-class midget submarines on Nazi warships Tirpitz, Scharnhorst, and Lutzow in northern Norway during World War II.

William Franklyn's voice was dubbed, as his voice was considered too upper class, and it clashed with that of John Gregson, who had the main role.

In this movie, the name of the vessel that carried the manned human torpedo chariots was called "Ingebord", but the actual one was named "Arthur".

The code-name of the actual World War II mission, on which this movie was based, was Operation Source. This operation utilized the Royal Navy's midget X-class submarines.

Opening credits: All characters and events in this film are fictitious. Any similarity to actual events or persons, living or dead, is purely coincidental.

Actor Donald Sinden could not actually swim in real life so it was ironic he should appear in a film primarily set at sea.