After an abrupt and violent encounter with a French warship inflicts severe damage upon his ship, a captain of the British Royal Navy begins a chase over two oceans to capture or destroy the enemy, though he must weigh his commitment to duty and ferocious pursuit of glory against the safety of his devoted crew, including the ship's thoughtful surgeon, his best friend.

Defiant's crew is part of a fleet-wide movement to present a petition of grievances to the Admiralty. Violence must be no part of it. The continual sadism of Defiant's first officer makes this difficult, and when the captain is disabled, the chance for violence increases.

"Under Ten Flags" is a WWII movie loosely based on the true story of the German navy commerce raider Atlantis, a converted Auxilliary Cruiser, and her Captain Bernhard Rogge. Atlantis, camouflaged as a merchant ship, cruised the South Seas ( Atlantic, Indian & Pacific) and sank or captured 22 merchant ships from May 1940 through November 22, 1941 when she was sunk by the British Cruiser HMS Devonshire. Rogge was one of the few German officers of flag rank who were not arrested by the Allies after the war ended. This was due to the very proper and ethical way he exercised his command of Atlantis. After the war he advanced to Rear Admiral in the West German Navy and became a high-ranking NATO commander.