Captain Karl Ehrlich (John Wayne) is the master of the elderly German steam freighter Ergenstrasse, in port at Sydney, Australia on the eve of the Second World War. Ehrlich is depicted as a patriot, a former career naval officer who lost his rank and position after falling out of favour with the current regime and refusing to support the Nazi Party. As his ship prepares for sea (or to be interned if war is declared) he meets with an old friend, British Commander Jeff Napier (David Farrar) and his fiancée Elsa Keller (Lana Turner).
Germany has invaded Poland, and war is imminent. As his ship prepares to slip away, Ehrlich receives a visit from the German Consul-General, who asks him to take with him a spy to prevent the spy's capture. It is only after the Ergenstrasse slips out of harbour in thick fog that Ehrlich discovers the spy is in fact Keller.
Old, slow and short on coal, the Ergenstrasse is seen as easy prey by the Australian Navy and by Napier in particular, who understandably holds a grudge. But Napier is the only man who does not underestimate Ehrlich. The wily captain leads his enemies on a chase across the Pacific Ocean, beginning with a run to the south to throw off pursuit, and pausing for supplies at an unmanned rescue station on Auckland Island. While there, Ehrlich's first officer, the pro-Nazi Kirchner (Lyle Bettger), murders three marooned seamen, but does not tell the captain about it. Napier discovers the bodies while in pursuit and believes his old friend is responsible. He vows to bring the German to justice as a war criminal.
Ehrlich burns the ship's lifeboats for fuel, upsetting the crew, then stops for wood at the fictitious Pom Pom Galli Atoll in mid-Pacific. While there, Ehrlich discovers that Kirchner murdered the fishermen and forces him to sign an account of his actions in the ship's log. The ship arrives at Valparaíso in neutral Chile, and Ehrlich encounters Napier, as his ship HMAS Rockhampton has pursued him from New Zealand.
Luck is with them as the Ergenstrasse, re-provisioned and fuelled, slips away in the darkness; the British forces waiting for them have been called away in support of the cruisers facing the German pocket battleship Graf Spee in Montevideo, Uruguay. Napier requests a transfer to the British Naval patrols in the North Sea, believing that Ehrlich must pass through the patrols in his attempt to reach Kiel.
For political reasons, German radio broadcasts a message from Lord Haw Haw that discloses the position of the Ergenstrasse as it passes Norway, thus giving up the ship and crew to the Royal Navy and to the waiting Napier, as his swifter passage home places the corvette under his command in Ehrlich's path. Napier tracks down Ehrlich's ship and sinks it in the North Sea, with Elsa and Ehrlich aboard, and with Kirchner as an unwilling participant in the short, one-sided battle. The ship's log is handed over to Napier by the survivors and proves Ehrlich innocent of the Auckland incident.John Wayne as Capt. Karl Ehrlich
Lana Turner as Elsa Keller
David Farrar as Lt Cdr. Jeff Napier RN
Lyle Bettger as Chief Officer Kirchner
Tab Hunter as Cadet Wesser
James Arness as Schlieter
Dick Davalos as Cadet Walter Stemme
John Qualen as Chief Engineer Schmitt
Paul Fix as Max Heinz
Lowell Gilmore as Captain Evans
Luis Van Rooten as Matz
Alan Hale as Wentz
Wilton Graff as Consul-General Hepke
Peter Whitney as Bachman
Claude Akin as Winkler
John Doucette as Bos'n
Alan Lee as Brounck
It was originally announced that Australian actor Michael Pate would play the ship's radio operator, but he does not appear in the final film.
The novel was published in 1948. Warner Bros bought the film rights. John Wayne was announced for the lead from June 1951 with Bolton Mallory reported as working on the script. Soon after James Warner Bellah was announced as working on the script.
Production of the film was delayed for a while. In August 1953 John Farrow, who had made Hondo with Wayne, signed as director. Frank Nugent rewrote the script.
Filming finally began in September 1954.
John Wayne later said Farrow "didn't really have a great deal to do with" Hondo because it was a Batjac production and "Everything was set up before he came on it. But he did direct Sea Chase and prove to me that he should not be put in charge of a producer-director position. He failed to tell the good story that was in the book. But now, we're talking about a matter of opinion and that's only my opinion. For some, he may be considered a fine director."
The fictional HMAS Rockhampton is played by HMCS New Glasgow, a River-class frigate built in Canada as a wartime emergency anti-submarine escort. She was placed in reserve in 1945, but in 1954 had recently been updated and recommissioned as a Prestonian-class frigate. This class has a classic wartime outline, similar to the Black Swan and Grimsby class sloops operated by the Royal Navy and Royal Australian Navy in 1939 including HMS Morecambe Bay and Wellington, which served in the Pacific, and is now a museum ship on the River Thames in London.
The script was adapted from a novel of the same name by Andrew Geer (1905–57), which in turn was based on an incident involving the 1929-built German Norddeutscher Lloyd steamer Erlangen (6101 tons). Under the captaincy of Alfred Grams, the freighter slipped out of Lyttelton Harbour (New Zealand) on 28 August 1939, on the very eve of war, ostensibly for Port Kembla, New South Wales, where she was to have filled her coal bunkers for the homeward passage to Europe.
She then headed for the subantarctic Auckland Islands, where she successfully evaded the cruiser HMNZS Leander and re-stocked with food and wood (cutting down large swathes of the Southern Rata forest). The freighter then made a desperate and successful escape, using jerry-rigged sails, to Valparaíso, Chile, in South America. She subsequently made her way into the South Atlantic, where, on 24 July 1941, she was intercepted off Montevideo by HMS Newcastle and scuttled by her crew.
Though using the same basic plot as the film, the book painted Kirchner as the hero and Ehrlich as the villain, essentially swapping their roles; the book portrays Kirchner and Keller as unintended victims of Erlich's obsession, though in both stories, the key characters all appear to go down with the ship at the climax.
A Bathurst-class corvette named HMAS Rockhampton was built by Walkers Limited in Queensland in 1942 for the Royal Australian Navy. She operated in Australian and New Guinea waters during the later years of the Second World War, three years after the events depicted in the film.