The H677 heavy enfilade 88mm gun casemate

One of the most fearsome types of defensive emplacements on the D-Day beaches was the H677 gun casemate, armed with the massive 88mm PaK 43/41 towed anti-tank gun. This type of casemate was officially designated as “Schartenstand fur 8.8cm PaK 43/41 ohne Nebenraume” and the first of this type was completed in March 1943. This type of bunker was designed for enfilade fire with a 2m thick wall protecting its embrasure from the sea. The powerful gun in this bunker could control the beach for 2-3km, so at Omaha Beach there was one of these on either end of the beach; other beaches typically had a single example of this type of heavy bunker.
Construction of this bunker was typical of the gun casemates found along the Normandy coast, basically a garage design with a large armoured access door in the rear and a large embrasure in the front to permit a wide field of fire of almost 60 degrees. The protective basis was Category B, meaning 2m thick concrete that offered protection from most army artillery and naval guns up to about 8in. cruiser weapons. These bunkers were essentially impervious to tank guns, except for the front embrasure and the rear armoured door.

​

There was a concrete apron in front of the gun embrasure, partly to prevent dirt and dust being kicked up when the gun fired and thereby obscuring subsequent firing, but also to minimize the risk of enemy artillery kicking up earth immediately in front of the embrasure from near misses. The bunker was designed to be enclosed with earth on both sides, while at the rear of the bunker, an earthen mound or protective concrete wall was erected to shield the rear armoured door. Generally, the roof was covered with earth for camouflage purposes. The upper edge of the bunker had curved sections of rebar protruding that were used to attach camouflage nets. Generally, a camouflage net was extended over the front of the structure to hide the embrasure. In some cases, the exposed concrete was camouflage painted. This was not a standardized procedure and depended largely on the local unit.
The construction of one of these bunkers required the excavation of about 150 cubic meters of soil and consumed 380 cubic meters of concrete, 17 tonnes of steel rebar and 4.5 tonnes of other steel. A total of 146 examples of this type of bunker were constructed on the Atlantic Wall, mainly in early 1944, with 55 of these in the Seventh Army sector in lower Normandy.