The Atlantic Wall utilized concrete shelters of all types, usually underground with a minimum of 3 ft of earth. Walls could be as thick as 6 ft 6 ins of reinforced concrete. Two shelters were constructed for the Kruschen Hedgehog but resemble the German wooden shelter with ferro-concrete reinforcement (Schurholz-Unterschlupf mit Stahlbetonverstarkung), in which the concrete roof extends around the basic shelter thus giving added protection against bombs and shells. This type of shelter was intended for semi-static/static Field Fortifications, perhaps more likely to found on inland stongpoints rather than the stronger shelters used for the beach defences.
Above: Left - plan of typical German sunken shelter. Middle and right - plans of the two sunken shelters prepared for Exercise Kruschen
The two examples on the Kruschen site are basically a 2 ft wide trench by about four ft deep which is capped with a 10” thick concrete roof. The trench sides are revetted with 2” scaffolding poles and corrugated iron sheets; the poles also support the concrete roof over the trench. The poles are held in place with a windlass. One has an ‘L’ shaped entrance at one end, which leads to a communication trench (crawl trench dimensions) while the other entrance is into a small pit. The second is constructed at one end of an existing large pit (old quarry?) and has a staggered entrance at one end which leads to a communication trench (crawl trench dimensions) while the other end opens into the large pit.
Above: Method of construction used for the Kruschen Hedgehog Deep Shelters
A much stronger shelter, with 3 ft 3” thick walls and roof, to a standardized design found along the English Channel Coast, was constructed as a target for the anti-tank gun range.
Above: Top four images - the shelter, along with floor plan / cross section, constructed to practice anti-tank gun shoots against visible concrete defences
Bottom three images - plan of standard concrete shelter found along the Channel Coast. The Kruschen example is clearly based on this