Submarine pen
（重定向自Sub pen）
![Surrendered German U-boats moored outside the Dora 1 bunker in Trondheim, Norway, May 1945](/Images/godic/202502/13/Uboatsafterthewar0235.jpg")
![Forced concentration camp labour at U-boat pens in Bremen, 1944](/Images/godic/202502/13/Bundesarchiv_Bild_185-23-21,_Bremen-Farge,_U-Boot-Bunker_Valentin,_Bau0235.jpg")
![Submarine pen at Bordeaux](/Images/godic/202502/13/Basesousmarine0235.JPG")
![U-boat pens at Brest](/Images/godic/202502/13/Concrete_U-boat_pens_at_Brest0235.jpg")
A submarine pen (U-Boot-Bunker in German) is a bunker that is designed to protect submarines from air attack. The term is generally applied to submarine bases constructed during World War II, particularly in Germany and the occupied countries, which were also known as U-boat pens (after the phrase "U-boat" to refer to German submarines).