Prior to this U-boats had to travel from ports in Germany to their patrol areas, losing valuable time in the long transits necessary.

Already a French naval base, Lorient had the facilities Dönitz needed, as well as numerous cafes and bars, and a red-light district.

[1] A special train loaded with replenishment supplies and ordnance, and the personnel to manage them arrived in Lorient at the end of June,[2] and the first U-boat, U-30 docked a week later.

This was a quayed inlet with a boat lift that could raise vessels out of the water, to be placed, via a turntable into one of twelve bays arranged in a circle.

The boatlift and turntable was designed to lift a pelagic trawler and could accommodate vessels up to 65 metres in length, just adequate to raise and carry a Type VII U-boat.

Work commenced in November 1940, and the installation comprised two wet docks capable of accommodating the larger Type IX U-boat.

At the same time, in the trawler port, two large above-ground bunkers were constructed to protect U-boats that may require repairs or refit.

[8] Royal Canadian Air Force records show 427 Squadron conducted raids from base in Croft, directly attacking the harbor.

Without resupply of fuel, weapons (e.g. torpedoes), and provisions, it became impossible for those U-boats to return to war patrols in the Atlantic Ocean.

Stosskopf was a German-speaking Alsatian Frenchman who had been the deputy director of naval construction at the base, and used this position to promote sabotage and to pass information on submarine movements to the Allies.

The site also the location of the City of Sailing exhibition centre(fr), named for yachtsman Eric Tabarly, and a yachting marina.