Construction of the U-boat bunker in La Pallice, the primary port of La Rochelle, started in April 1941. The construction of the 10 U-boat pens lasted two years, but already from November 1941 the first U-boats began to arrive. The 3rd German U-boat flotilla had its headquarters in La Pallice and remained here until August 1944, when the flotilla moved to Norway because of the Allied landings in Normandy (d-day) in June of that year.