The Bases in France
The French harbours on the west coast were captured by the German army after the stunning victory over the allied forces in May-June 1940. Almost right away widespread preperations for an all-out U-boat deployment from those bases went into action.
5 U-boat bases were established in the Bay of Biscay in 1940 and 8 U-boat flotillas were either moved to France or formed there in 1941 and 1942. The first were the 1st at Brest, the 2nd at Lorient and the 7th in Saint Nazaire in June 1941, followed by the 3rd at La Rochelle and the 9th at Brest in October 1941. In 1942 the last 3 flotillas appeared in France with the 10th at Lorient in January, the 6th at St. Nazaire in February and finally the 12th flotilla was formed in Bordeaux in October 1942.
The bases in France (see map) gave the Kriegsmarine major advantage in the U-boat war in the Atlantic, no longer would the boats have to circumnavigate the British Isles just to reach the convoys nor pass through the dangerous Channel. This greatly increased their fighting range and striking power when compared to the German bases. From late 1940 and early 1941 most of the famous U-boats operated from the French bases.
The Kriegsmarine completed 1,149 major U-boat overhauls and operated hundreds of U-boats from the French bases in the Biscay during the war.
In 1943 a base was also established at Toulon in the French Mediterranean. It was the home of the 29th Flotilla for over a year.