As World War II rages on, the battle continues above and under the seas. When a damaged U-Boat is forced to surface and set to scuttle, Royal Marines boarding parties have to race against time and obstacles to secure the vessel and seize the precious Enigma cipher machine and radio code-books, before the stricken vessel sinks beneath the waves!

This expansion pays tribute to, and features, Royal Marines of the Commando Brigade with raiding missions and incursion skills, reflecting the high-intensity, close-quarters warfighting aboard a sinking ship.