Under Ten Flags

In London in 1941, Adm. Russell struggles to locate and destroy the German raider Atlantis , which has been blowing up Allied warships in the Pacific Ocean. At sea, the Atlantis , led by Cmdr. Reger, is employing its customary ploy of sailing under camouflage in order to sneak up on enemy ships, which it can then destroy. To that end, the Atlantis is disguised as a Japanese cruise ship when they pull up alongside the British ship Christina and, after revealing their true flag, open fire. As the Christina 's sailors abandon ship at the order of Capt. Windsor, Reger takes them prisoner aboard the Atlantis and sends a signal in British code reversing their earlier distress call. Windsor fears poor treatment, but Reger scrupulously maintains humane conditions for his prisoners, earning him Windsor's respect. When information about the raid reaches Russell, he is able to determine from the details that the Atlantis is a surface vessel instead of a submarine, but the ship's appearance remains a crucial mystery. Soon after, Reger sights the merchant ship Abdullah and calls for its surrender. The captain raises a white flag, but then, greedy for a British reward, opens fire. Reger is forced to return fire, causing the death of many innocent passengers. The remaining passengers, including orphan children tended by nuns, the flirtatious Zizi and Jewish couple Sam and Sara Braun, are rescued and taken aboard. When Reger informs the Abdullah 's captain that he is being placed under arrest for endangering his passengers, Windsor agrees to stand witness against the man. Weeks later, the Atlantis , now disguised as the Calypso from Bombay, comes upon a British warship that refuses to allow it to pass. When the British captain insists on sending a search party on board, Reger is compelled to attack, instructing his men to guard to the safety of the civilians aboard the Atlantis . Soon after, Reger receives a coded message from a German U-boat seeking help, but when he asks it to name its position using the secret code called the "flower grid chart," the signal ends. Russell, who has sent the falsified signal in order to trap the Atlantis , realizes that he will never destroy the ship without the flower grid code. Knowing he is being hunted, Reger, who has now been at sea for over a year, stops the ship mid-ocean for a month until the Admiralty loses track of it. While Russell and intelligence director Col. Howard plan a covert operation to steal the code, at sea Zizi begins a romance with Lt. Krueger, not realizing that he is a Nazi. When the Abdullah captain reveals to Krueger that Sam and the pregnant Sara are Jewish, however, Krueger's anti-Semitism disgusts Zizi. The lieutenant insists to Reger that the Brauns be killed, but Reger refuses, stating that he treats all his prisoners equally. Meanwhile, at the German headquarters in Paris, British secret agent Knoche, who has undergone plastic surgery to resemble the German officer in charge of the flower grid code, begins the dangerous mission of infiltrating the office and photographing the code. Although he is nearly caught, Knoche escapes with the film, only to encounter outside the German officer he is impersonating, where he kills the man to evade detection. Meanwhile, Sara has given birth to her daughter, and to keep the family and the rest of the prisoners safe, Reger captures a Norwegian ship to transport them to land. Although sending the ship to a German-controlled port will keep the ship and passengers under German control, Reger insists on sending them to a neutral port, where the Brauns will not be threatened. The ailing Windsor voluntarily remains with Reger, and as the others sail away on the Norwegian ship, sing Brahms's "Lullaby" to Reger, acknowledging the debt they owe him. Later, armed with the secret code, Russell is able to pinpoint the position of the Atlantis , but in order to trap the wily commander, Russell knows he must use extreme caution. To this end, he painstakingly plans his trap, finally sending the HMS Devonshire to intercept the ship. By this time, Reger, who has now been at sea for almost two years, has rendezvoused with a German submarine. Spotting the Devonshire , he camouflages his ship as the British Polyphemus and plants his seamen on deck disguised in women's dresses. Hoping to lure the Devonshire close enough to attack it with the submerged submarine, if necessary, Reger allows the heavily armed warship to draw closer. He sends a "cease" signal in British code, forcing Russell in London to scramble to discern whether or not the signal came from the real Polyphemus . When Russell finally receives word from the real Polyphemus , he orders the Devonshire to open fire on the Atlantis . Krueger demands that they return fire, but Reger, knowing that remaining quiescent will leave the British unsure of whether or not they have attacked the correct vessel, refuses and orders his men to abandon ship. As Reger considers going down with his ship, a wounded Windsor collapses in his arms and instructs him to save himself, as a worthy soldier and a good man. Before jumping off, Reger instructs the remaining sailors to set an explosive so that the Atlantis will be completely destroyed, and thus unable to be identified. Back at the Admiralty, Russell realizes that he will never be sure if he has destroyed the correct ship, and grudgingly admires his worthy rival.