U-boats, like Allied submarines, were different from today's nuclear subs which can remain underwater for months. WWII subs were more like regular boats with diving capability. They had to return to the surface periodically.

When submerged, WWII subs would creak and groan. Men had to live in cramped spaces. Showers were usually permitted only once a week. Sometimes the stale air in the sub was freezing cold. Sometimes it was blazing hot with nearly 100% humidity. The possibility of losing one's life on a submarine was an ever-present reality.

German U-boats were usually identified by numbers. U-110, on patrol in the North Atlantic on May 9, 1941, was having a good trip. Having sunk two Allied ships in the convoy passing to the south of Iceland's Cape Farewell, Lemp left his periscope up longer than usual. He probably was gloating a bit over his successful kills. It would be the last time he looked through the periscope of U-110.