The construction of Underzeebootbunker Valentin was part of a larger Nazi strategy to use U-boats to attack Allied fleets and change the course of the war. From 1939, the German Kriegsmarine was tasked with sabotaging Allied supply routes across the sea. According to a German Naval Staff memorandum from October 1939, British overseas trade was the enemy’s weakest point, and U-boats were meant to sever this route through attacks.

The conflict between the German Kriegsmarine and the Allied fleet, known as the Battle of the Atlantic, lasted from 1939 to 1945 and was the longest military campaign of World War II. Allied merchant ships were primarily destroyed by large-scale submarine attacks. During Operation Paukenschlag, Nazi Germany’s first offensive against American shipping in January 1942, 609 Allied ships were sunk, and around 5,000 merchant seamen lost their lives.

Demand for U-boats surged. While Germany had 57 U-boats in 1939, more than a thousand were added during the war. Ultimately, three-quarters of them were sunk.

To speed up production and protect new U-boats from bombings, the decision was made to build a series of submarine bunkers. In 1943, construction began on Bunker Valentin in the current district of Rekum. The bunker was designed to enable rapid production, with entire U-boats assembled inside.

An estimated 10,000 forced laborers were used for the construction. They came from all over Europe: Eastern and Western European forced laborers, Soviet prisoners of war, Italian internees, concentration camp prisoners, and workers from the Bremen labor education camp. Conditions were extremely harsh, and many died.

In March 1945, just before the end of the war, the bunker was heavily damaged by Allied bombings. The project was never completed, and no U-boat was ever built there. Today, Bunker Valentin remains visible and is the second-largest above-ground bunker in Europe.