In the Atlantic German U-boats operate sucessfully against Allied convoys. One important reason: the Allies are unable to crack the German war codes.
When American reconnaissance agents pick up the SOS-signal of a wrecked U-boat, the Americans want to seize the chance. The doomed ship carries an Enigma Machine, a special coding device that allows German forces to send messages that can't be read without a similar encryption mechanism. Obtaining a working Enigma device would be invaluable for the Allied war effort, so a U.S. sub is sent out to seize the engima coding machine.
A small crew of American sailors is conscripted for this special mission. The crew is led by Lt. Andrew Tyler, who's smarting none-too-graciously at having been denied his own submarine command, and doesn't much like Lt. Hirsch, the German-speaking mastermind behind the daring plan. With the exception of grizzled Navy lifer Chief Klough, Tyler's men are young and wet behind the ears, right down to Wentz, the fresh-faced farm boy tapped for a pivotal role in the operation purely because he's fluent in German. The plan: By masquerading as Nazi's convince the U-boat's crew they're a German rescue squad, overpower them while they're off guard, grab the coding device and scuttle the ship. Naturally, the plan goes horribly awry, and Tyler must get his men (and the precious machine), out of a series of increasingly hopeless-looking situations - since the German forces have already picked up the sub's distress signal and are en route to rescue their comrades.