guns, with FL (Flak or anti-aircraft) and V (Versorgung or support) for other emplacements, using thicknesses varying from 1.2m to 2.2m. The Luftwaffe simply added a letter L to all their designs, copying 1938 designs before creating their own series. The standardisation greatly simplified the manufacture of equipment, the supply of materials and the budgetary and financial control of the construction as well as the speed of planning for construction projects. Development of Regelbau designs from 1936 to 1940 Following the occupation of German territories west of the Rhine, fortress engineers began the construction of the Siegfried Line in 1936. In doing so they were able to benefit from their earlier experience of bunker construction. In compliance with the Versailles Treaty, they had already built the Wetterau-Main-Tauber position and Neckar-Enz position before 1936. When, in 1936, construction started on the Siegfried Line itself, they were able at the outset to utilize designs from the two earlier fortifications. From these existing plans, fortress pioneers rapidly developed improved bunkers that were built from 1937. 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. These new designs were achieved largely by simplifying and reducing the number of Regelbau types. This new building phase was called the Limes Programme. 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. Plans for the Limes Programme did not envisage the inclusion of the cities of Aachen and Saarbrücken and they therefore ended up in front of the planned line of fortifications. That changed in 1939 with the Aachen-Saar Programme. From 1939, yet more new Regelbau bunkers were designed for the construction programme that saw increases in the construction thicknesses. From then on, only bunkers that met the in "B new" and "A" standards were to be built. With the outbreak of the Second World War on 1 September 1939, priorities for the construction of the Siegfried Line changed. The renewed shortage of raw materials led to the development of a new series of Regelbau designs, the so-called wartime standard designs or Kriegsregelbauten. After the