During 1943, fortification engineers began to experiment with an advanced type of reinforced concrete using wire under stress instead of the usual steel reinforcing bars. This promised to be significantly lighter, leading to plans for a fully traversable concrete turret to get around the limitations of traverse in fixed casemates. An experimental example was completed outside Paris in early 1944, and the first concrete turrets began to be built on the Atlantic Wall. starting with one near Fort Vert to the east of Calais. However, the technology appeared too late in the war to be widely used.
The army did not favor fixed guns like the navy and preferred to use conventional field artillery. This was based on the premise that the batteries could be moved from idle sectors to reinforce the defenses in sectors under attack. The army pointed to previous examples of British amphibious attack, such as Gallipoli, where the amphibious assault became a protracted campaign. At first, the army preferred to use simple kettle mounts patterned on the World War I style, which were simply circular concrete pits with protected spaces for ammunition. The gun itself was completely exposed, but the gun pit was supported by fully protected crew bunkers, ammunition bunkers and a fire-control bunker. This was the predominant type of army coastal battery configuration on the Atlantic Wall from 1942 into early 1943. However, as Allied air activity over the French coast increased in intensity, the vulnerability of these batteries to air attack became the subject of some concern. Intuitively it seemed that the navy’s casemates offered better protection from air attack than the kettle positions. However, based on actual combat experiences, some of the fortification engineers argued that this was not the case. The confined casemate tended to concentrate the blast of any bomb that landed near the gun opening, and it was found that guns in open pits were almost invulnerable to air attack except for the very rare direct hit on the gun itself. In the wake of the Dieppe raid, however, the policy shifted to full protection of the army coastal batteries in casemates. These resembled the navy casemates except that they generally had a large garage door at the rear to permit easy removal of the gun for transfer to other sectors if needed.
The army fortification engineers had established protection standards during the Westwall program based on steel-reinforced concrete (Beton-Stahl). Category E fortifications were based on walls and ceilings 5m thick but this standard was uncommon and used mainly for strategic command posts such as the Führer bunkers. The highest level for tactical fortifications was A, which used a 3.5m basis, and this was confined to large, high-priority structures such as the U-boat bunkers and some key facilities such as the heavy gun batteries on the Pas-de-Calais and special military hospitals. Most Atlantic Wall fortifications were built to the B standard, which was 2m thick, proof against artillery up to 210mm and 500kg bombs. Many minor bunkers, such as the ubiquitous tobruks, were built to the slightly lower B1 standard of 1 to 1.2m since these structures were partially buried. The designers attempted to minimize the amount of steel necessary in construction, so aside from the steel reinforcing bars (rebar), steel plate and especially steel armor plate was kept to a minimum. A standardized family of small armored cupolas, doors, and firing posts had been developed during the Westwall program and these were used on the Atlantic Wall as well. Most personnel bunkers and other enclosed bunkers built in 1942–43 were also provided with protection against gas attack both by systems to seal the structure from outside air, as well as filtration systems. Obviously, this was not possible with large gun casemates, but the associated crew bunkers typically had gas protection.
The Fortification Engineer Corps in Berlin designed a family of standardized bunkers for typical applications. Some of these were based on the earlier Westwall program but the majority were newer designs. The original Westwall fortifications had been designated in the OB or Vf series for Offene Bettung (open platform) or Verstarkfeldmässig (reinforced field position). Although some of these designations were retained during the construction of the Atlantic Wall, a new series of designations emerged. There is some disparity in how these designs are identified so for example, the “611” bunker design is variously called Bauform 611 (construction plan 611); R611 (Regelbau 611: construction standard 611) or H611 (Heer 611: Army 611) to distinguish army bunkers from air force (L: Luftwaffe) and navy (M: Kriegsmarine) bunker designs. There were about 700 of these standard designs of which about 250 were used on the Atlantic Wall. It should be mentioned that these designs were often modified in the field to better match local terrain contours. Besides the standardized designs, there were localized variations of standard plans as well as entirely new designs, sometimes identified with an SK suffix for Sonderkonstruktion (special design).
The standard plans covered a variety of functional types. These are by no means the only categories of defensive fortifications, but cover the main types.
| Gefechtsstand | Command post |
| Leitstand | Fire-control post |
| Beobachtungstand | Observation post |
| Nachrichtenstand | Communication post |
| Kampfstand | Combat post |
| Schartenstand | Artillery casemate |
| Ringstand | Tobruk |
| Unterstand | Bunker |
The table opposite lists the army bunkers deployed under the three army headquarters (AOK) in France in June 1944. The common types are listed by their designations while less common types are lumped together under their function. This list does not include the category of “reinforced field position” such as tobruks, and open gun pits such as the Vf600 types, which were not considered “bombproof”.
| - | AOK 15 | AOK 7 | AOK 1 | Sub-total |
|---|---|---|---|---|
| Personnel | ||||
| H621 (501) single group | 393 | 447 | 266 | 1,106 |
| H622 (502) double group | 433 | 398 | 202 | 1,033 |
| H668 small bunker for nine men | 84 | 59 | 70 | 213 |
| Other personnel bunkers | 47 | 56 | 16 | 119 |
| Munitions | ||||
| H607 ammunition | 102 | 18 | 70 | 190 |
| H134 ammunition | 236 | 66 | 21 | 323 |
| Other ammunition bunkers | 6 | 28 | 28 | 62 |
| Medical | ||||
| Medical and support bunkers | 72 | 57 | 42 | 171 |
| Communication | ||||
| Communication posts | 20 | 10 | 6 | 36 |
| Command | ||||
| Command bunkers | 98 | 58 | 36 | 192 |
| Artillery observation | ||||
| Artillery observation bunkers | 54 | 34 | 46 | 134 |
| Weapons shelters | ||||
| Weapons garages | 52 | 69 | 30 | 151 |
| Gun casemates | ||||
| H669 field gun | 44 | 189 | 141 | 374 |
| H612 field gun/PaK | 133 | 60 | 178 | 371 |
| H667 50mm | 35 | 193 | 118 | 346 |
| H630 (H105) MG | 178 | 89 | 10 | 277 |
| H671 field gun | 38 | 38 | 112 | 188 |
| H634 (H112) turreted MG | 52 | 66 | 2 | 120 |
| H680 75mm PaK 40 | 24 | 40 | 47 | 111 |
| H677 88mm PaK | 24 | 36 | 43 | 103 |
| Other gun types | 239 | 165 | 82 | 486 |
| Total | 2,364 | 2,176 | 1,566 | 6,106 |