U-boat pens

U-boat pens were large, heavily fortified underground shelters built by Nazi Germany during World War II to house and protect their submarine fleet. Located primarily in coastal regions like Saint-Nazaire and Brest, these structures featured thick concrete walls and roofs, making them resistant to Allied bombings. The pens allowed submarines to be maintained, repaired, and launched safely out of enemy sight, ensuring rapid deployment during wartime. Their construction reflected the strategic importance of U-boats in disrupting Allied shipping and supply lines across the Atlantic.