Many of the older fortifications on the islands were incorporated into the new defenses, after being reinforced with concrete. OT built over 8 km of concrete anti-tank walls wherever there were no preexisting granite walls along the beaches. It also installed the famous Mirus Battery of 305-mm guns on the island of Guernsey. However, it did not get around to placing a 380-mm battery on the key island of Jersey so other batteries had to assume the task of sealing the channel between there and the Cotentin Peninsula. As priority until 1943 was given to the submarine pens in France the OKH assigned no construction battalions to OBW General Witzleben, who had to borrow workers from the navy to build his land defenses. Before the end of 1941 Witzleben directed his army, corps, and division commands to carry out reconnaissance for suitable coastal positions and begin construction. By this time many of the old French coastal positions were put back into service.
Major construction on the Atlantic Wall began in 1942, after Wilhelm Keitel, Chief of the Wehrmacht High Command, called for the construction of a “West Wall” extending from the Arctic to the Atlantic. In that year the building regulations for concrete defensive positions had become standardized and many of the designs found successful on the West Wall were incorporated into the new coastal defenses. Field Marshal Gerd von Rundstedt returned to active duty, replacing Witzleben as OBW in March 1942.
As in the case of the East and West Walls, Hitler was not able to resist the temptation of adding his own personal touch to the Atlantic Wall. Thus in August 1942 he outlined the framework of the Atlantic Wall in Directive Number 40. He also exhorted his compatriots to show “fanatic” energy in the defensive effort and ordered the creation of strong points for thirty to seventy men armed with machine guns and anti-tank weapons. The new positions were to be able to withstand heavy bombardment and have inter-locking fires. The Führer further contemplated the completion of 15,000 concrete positions to be defended by 300,000 men. However, Fritz Todt, head of the OT, expressed doubts about his ability to complete more than 6,000 positions before the end of the spring of 1943. Hitler ordered Todt to concentrate his efforts on the submarine pens first, then the ports, the Channel Islands, and finally the open beaches.
The German High Command theorized that no invasion could succeed if seaports were not taken to lend logistical support. Their reasoning was based on historical precedent and was further supported by the Allied invasions of North Africa in late 1942 and Sicily and Italy in 1943. They never imagined that the Allies would build their own mobile harbors, the Mulberries.
In October 1943, Hitler ordered secondary defenses to be set up within 15 km of the beaches. However, these plans were not given priority, even though their purpose was to back up the front line positions and prevent a breakout. Meanwhile, work continued on fifteen fortress areas in Norway, which further depleted the available resources for the French coast.
The port strategy and existence of beaches convenient for invasion, caused the Germans to funnel their energies into the fifteenth Army’s sectors between the Seine and the Schelde, which offered the most direct route to the Ruhr. Only late in the construction effort did the Normandy coast, defended by the seventh Army, receive much attention.
In July 1942, OBW selected the fifteen Defense Sectors that were designated as fortresses by Hitler, along with the Channel Islands. They included:
Netherlands: Den Helder, Ijmuiden, Hoek van Holland and Vlissingen on Walcheren Island.
France: Dunkirk, Calais, Boulogne, Le Havre, Cherbourg, St. Malo, Brest, Lorient, St. Nazaire, La Rochelle-La Pallice, and Royan at the mouth of the Gironde.
More concrete was poured on the Atlantic Wall positions in 1940 than in 1941. However, the amount of concrete used between January and July 1942 was more than triple the amount used in the two previous years combined, topping over 700,000 cubic meters. The consumption rose to over 200,000 cubic meters per month in June 1942 and did not drop below that until June 1944. The peak month was April 1943 with over 760,000 cubic meters used, gradually dropping down to just over 200,000 cubic meters at the end of the year and rising back up in April 1944. The bulk of the German coastal defenses were built between the spring of 1943 and D-Day.
Starting in 1943, the German fortification effort began to face serious setbacks. Between 1943 and 1944, many of the workers engaged in building fortifications were sent to Germany and other occupied territories to repair the damage inflicted by the Allied air campaign. In addition, preparations were made in 1943 to defend the Mediterranean coast, which further drained the Reich’s resources. However, despite these problems, Field Marshal Erwin Rommel pushed forward construction plans for 1944 and achieved maximum results after taking over Army Group B.
Before Rommel’s take-over, most of the work had been concentrated on the Festungsbereich or fortress areas. When Rommel took over in 1943, the controversy over strategy was reopened. According to the previous policy, the German forces were committed to form a large tactical and strategic reserve whose mission was to counter-attack and drive any invasion force back into the sea. However, based on his past experiences in Africa, Rommel concluded that Allied air power would make such a strategy impossible. He decided, therefore, that every effort should be made to defend the shoreline and to transform the intermediate areas between Defense Sectors into positions more substantial than mere outpost lines.
OBW Rundstedt tried to find a middle ground between Rommel’s ideas and those of his opponents like General Geyr von Schewppenburg of Panzer Group West. Thus Rommel was allowed to proceed with the construction of the Atlantic Wall even though he was prevented from pushing all available units as close as possible to the beaches. Rommel ordered his forces to lay down millions of mines, more than tripling the number placed before 1944, and set up thousands of obstacles at possible landing sites. He also closed the vulnerable gaps between fortress areas.
Every significant coastal port was fortified. The ports of Ijmuiden, Hoek van Holland, Dunkirk, Calais, Le Havre, Cherbourg, St. Malo, Brest, Lorient, St. Nazaire, and La Rochelle-La Pallice and the Channel Islands were declared fortresses by March 1944. Small fishing harbors were defended but not heavily fortified.
Even though French citizens were barred from the construction sites, information leaked out, including a German map showing the major positions. In addition, Allied reconnaissance flights detected many of the defensive structures. However, bombing had little effect on the great submarine pens until the huge block-buster bombs came into use.
In 1943 a new offensive element made its debut on the Atlantic Wall: the V-1 missiles. Their launch sites, consisting mainly of concrete installations, were strung out from the Channel Islands to the Calais area. In 1944 V-2 missile sites were added to the V-1 rocket bases. Some of these locations, like the complex at Wizernes which was built into a hill, were quite impressive. The only site for the secret V-3 long-range gun was in Minoyecques, not far from Wizernes in the Calais area, and was not finished in time for D-Day.
By May 1944, the OT had completed another 5,000 concrete structures on the French coast, including in southern France. These positions were in addition to 8,500 existing structures on the Atlantic and Channel coasts. The fifteenth Army occupied the most heavily defended sectors located between the Seine estuary and the Dutch border. It had more than twice the number of heavy and medium artillery pieces of the seventh Army, which held the much longer coastline of Normandy and Brittany.
On the home front, the defenses of the German Bight or Helgoland Bay, were not built until late 1944. Some gun batteries had been shifted from Germany to France between 1940 and 1941.
In the Eastern Mediterranean, the Germans set up some coastal defenses on the Greek mainland. In addition, OKW sent officers of the Fortress Engineers and Coastal Defense Staff South to advise the Bulgarians on coast defense, and the Italians on the fortification of the Aegean Islands. After Italy surrendered in September 1943, the Germans occupied many of their coastal fortifications.
In June 1944, the Atlantic Wall was still incomplete. Troops and civilian workers were still toiling over many of the obstacles. In addition, only 6.5 million of the projected 40 million mines had been laid. By the spring of 1944, OKW and OBW had completed only 10,500 of the 15,000 fortified installations Hitler had ordered (not including Norway). According to Colin Partridge, almost 6,000 smaller positions were also completed. This number included over 3,700 Tobrucks and 780 tank-gun platforms and bunkers.
Thus in 1944, the critical areas of the Atlantic Wall presented a formidable challenge indeed. Any assault directed at the defenses of the major or minor ports would have been tantamount to suicide, which is why the Allies did not seriously consider such a move. It is true that emergency plans such Plan Rankin A through C called for airborne troops and other units to capture Le Havre, but they were only to be set in motion in the event of a German collapse, when resistance would be minimal.