Regelbau

The reasons for this were continual developments in weapon technology as well as the availability of armoured components and raw materials (steel) in general.

[1]: 17 Whilst constructions were undertaken and planned by the OT for the Heer (army), the Kriegsmarine (navy) and Luftwaffe (airforce) would also man some of the fortifications, and they had their own designs and designations of fortifications, the Navy used M (Mittlere or Medium) for normal sea defence batteries with S (Schwere or Heavy) for the larger calibre guns, with FL (Flak or anti-aircraft) and V (Versorgung or support) for other emplacements, using thicknesses varying from 1.2m to 2.2m.

[2] Following the occupation of German territories west of the Rhine, fortress engineers began the construction of the Siegfried Line in 1936.

This building phase was named the Engineer Construction Programme and was characterized by bunkers built to B1 standard thicknesses (see above).

Since the thickness of these structures was soon considered to be too weak and because there was a large number Regelbau designs (and hence confusion), new types were developed and implemented from 1938.

The fortress engineers were no longer in charge of construction; instead Organization Todt (OT) took over, promising Hitler it would deliver the number of structures he wanted.

A mass of equipment was needed, cement, sand, gravel and steel to construct the concrete fortifications, weapons and armour plate for defence and hundreds of thousands of workers.

[2]: 51 The labour came from an expansion of the Organisation Todt, who contracted with building construction companies from Germany and occupied countries to undertake the work.