The film's storyline concerns the Battle of the River Plate, an early World War II naval engagement in 1939 between a Royal Navy force of three cruisers and the German pocket battleship Admiral Graf Spee.

In the early months of the Second World War, Nazi Germany's Kriegsmarine sends out merchant raiders to attack Allied shipping.

The British initially demand the Uruguayan authorities send Graf Spee out to sea within 24 hours, but once they recognise that reinforcements can arrive for an impending second battle they change strategy and lobby for an extension for the Germans.

The producers had the advantage of having elements of the Mediterranean Fleet of the Royal Navy available for their use, and USS Salem to play the part of Admiral Graf Spee, although she had a different number of main turrets.

The producers did make use of a 23-foot (7.0 m) model of Salem (with details only on the side being shot) in a six-foot (1.8 m)-deep tank at Pinewood Studios for scenes depicting hits during the battle, and also for the blowing-up of Admiral Graf Spee, which was assembled from multiple takes from different angles.

[10] In an early scene, it is claimed that Admiral Graf Spee is being disguised by the ship's carpenters – using features such as a false funnel – as an American cruiser, a trick typical of commerce raiders.

[12][13] The US Navy would not allow any Nazi insignia to be displayed on Salem so the wartime German flag being hoisted and flown was filmed on a British ship.

Cumberland was a disarmed trial ship without her 8-inch gun turrets at this time and was refitted with lattice masts, but is recognizable as the last of the three-funneled heavy cruisers to remain in service.

The use of real ships allows the film to pay particular attention to detail even though Admiral Graf Spee was portrayed by the American heavy cruiser USS Salem, which mounted 3" smaller main guns, is considerably greater in tonnage, 100' longer, and quite visually distinct (in bow, shearline, and having two forward triple turrets instead of the single forward turret of the Deutschland-class cruisers) from the German Pocket Battleship.

This emphasis on realism includes the warning bells ringing before each salvo, the scorching on the gun barrels after the battle, and the accurate depiction of naval procedures.

Similarly, although the scene when Harwood meets with his captains on board Ajax is fictional, it was created for the movie in order to explain the tactical situation to the audience.

In reality German gunfire did not "straddle" Exeter until 0623, after three salvoes, and her main armament fire was not "split" between the British ships until 0630, although these events are shown happening immediately.

[citation needed] Commodore Harwood is shown wearing the sleeve rings of a rear admiral from the start, although he was only promoted to this rank after the battle.

[citation needed] The Battle of the River Plate only obliquely hints at one aspect of the story: the death of Captain Hans Langsdorff after he scuttled his ship.

[citation needed] Prior to the destruction of the Graf Spee, the German crew were seen rowing away from the ship whereas in reality they were taken off by an Argentine tugboat.

In addition a Norwegian merchant ship reported the Graf Spee heading for South America before being spotted by lookouts but this is omitted.

The royal premiere was held at the Empire Theatre, Leicester Square (now Cineworld) on 29 October 1956 in the presence of Queen Elizabeth II, Princess Margaret, Marilyn Monroe, and Victor Mature.