Direct after they invaded europe the germans incorporated enemy batteries (Beutebatterien) and positions to defend ports and strategic positions. Later reinforced with german weapons with better performance.
In 1940 building of U- and S-Boot-Bunkers started to protect the fleets.
At the beginning of 1941 the fortification of the Channel Islands was ordered. In the end of 1941 the "Neue Westwall" was ordered after some attempts of England to land in Norway. This are the early steps of the Atlantikwall with focus on 1.) Norway, 2.) Belgium and France, 3.) Denmark and Netherland and last the German seeshores.
In 1942 the name Atlantikwall was first used for the giant task to secure the beaches from Norway until the border of Spain.
There were several Bauprogramme:
05/1943-09/1943 2. Bauprogramm
10/1943-04/1944 2. Winterausbauprogramm