The French naval bases at St Nazaire and Lorient, occupied by the Germans in June 1940, quickly became the homes of massive U-Boat fortresses - nearly indestructible submarine pens, built mostly by slave labour. From these bases, the U- boats struck merchant shipping at few will from the Mediterranean to the North Sea. Thousands of vessels were lost, along with vital war material from the US destined for Britain and the Soviet Union. It became a desperate battle waged on land, air and sea. The Royal Air Force began an all-out bombardment of the two ports.
Despite their extensive efforts - and those of the Americans who joined them in 1942 - the fortress would survive, surrounded by decimated French towns and countryside - and they continue to stand today.
