German design and placement of fortifications in WW2 was influenced by the emphasis on offensive operations.
Therefore, fortifications were seen as an extension of offensive capability and not just a defensible position. The German preference was for smaller, scattered fortifications in-depth rather than large extensive complexes. Bunkers such as observation posts, machine gun nests, anti-tank emplacements are common but usually small and rarely housed multiple installations.
Bunkers and fortifications are viewed as opportunities to allow a minimum of personnel to defend a section or area, thus freeing others for offensive operations.German emphasis on offensive power gives priority to fields of fire or observation. If the bunker is used for supply or merely housing personnel, the protective and camouflage aspects of the terrain are considered. To minimize vulnerability to attack from above (either high angle weapons such as mortars or howitzers, or bomb attacks from aircraft) the bunkers are kept to a minimum size, usually just one gun or squad.
In general the preferred materials are concrete and steel. However, depending on availability, wood, brick, masonry or earth are used. When concrete and steel is used, the standard thickness of walls and roof are 6 feet 6 inches (2 meters),but may vary depending on bunker purpose and availability of materials.
Author: Binhan Lin
Article and Image Source: http://www.cmhweb.org