 Alarmed by the raids on St Nazaire and Dieppe in 1942, Hitler ordered the construction of fortifications all along the Atlantic coast, from Spain to Norway, to protect against an expected Allied invasion.He envisioned 15,000 emplacements manned by 300,000 troops, but due to shortages, particularly of concrete and manpower, most of the strongpoints were never built.As the expected site of an Allied invasion, Pas de Calais was heavily defended.