Deadly Games' follow-on to their 1994 game U-Boat, takes the player to the shores of North America for what the U-Boat skippers called "The Happy Times".
From the manual:
DRUMBEAT is a campaign game recreating a series of U-boat patrols in the North Atlantic Ocean, The United States of America has just entered the war and Admiral Dönitz of the German Navy has his eye clearly focused on the rich opportunities awaiting him along its largely unprotected Eastern shores. This game can take you as far North as the Arctic Ocean and as far South as the Caribbean Sea. But you must stay alive to get there.