The Keroman U-Boat Bunker K3 is a massive concrete fortification located in Lorient, France, built during World War II as part of the German U-boat base complex. Constructed between 1941 and 1943 by the German Navy (Kriegsmarine), this bunker was designed to protect submarines from Allied air raids and served as a critical component of the Atlantic Wall defenses. The structure features thick reinforced concrete walls and massive blast doors, typical of Regelbau bunker designs of the era.
After the war, the French Navy continued to use the facility until the 1990s, and today it stands as a historical monument open to visitors, offering insight into the strategic importance of Lorient during the U-boat war.