Some 20 years after that loss, the United States and much of the world has now been split between Japan and Germany, the major hegemonic states. But the tension between these two powers is mounting, and this stress is playing out in the western U.S.

A German submarine hunts allied ships during the Second World War, but it soon becomes the hunted. The crew tries to survive below the surface, while stretching both the boat and themselves to their limits.

In the midst of World War II, the battle under the sea rages and the Nazis have the upper hand as the Allies are unable to crack their war codes. However, after a wrecked U-boat sends out an SOS signal, the Allies realise this is their chance to seize the 'enigma coding machine'.