The submarine Sea Tiger is sent out to sink a Nazi battleship which is due to leave Bremerhaven for the Kiel Canal, en route to the Baltic. The sub’s instructions are to intercept her off the German coast before she enters the canal. Too late for this, the lieutenant in charge decides to brave the dangers of the Baltic and attack the battleship when she emerges at the other end of the canal. Owing to depth charges from accompanying destroyers, the attack results in a leakage in the sub’s oil tanks and the Britisher decides to blow her up and escape to Denmark.
One of the seamen remembers there is a port on a nearby Danish island where there may be a tanker in dock. Donning the uniform of a dead German airman, he lands on the island, finds a tanker and signals to his ship to come in shore. They refuel and return home, and only then discover they have sunk the German vessel they were after.
John Mills enacts the lieutenant with not only requisite dignity, but with a human touch. But it is Eric Portman, as the seaman, who has the outstanding role and scores best. Rest of the cast gives excellent performances, while direction and production are above par.