The Atlantic Wall (German: Atlantikwall) was an extensive system of coastal fortifications built by Nazi Germany between 1942 and 1945 along the western coast of Europe and Scandinavia as a defense against an anticipated Allied invasion of the mainland continent from Great Britain.

Today, the ruins of the wall exist in all of the nations where the wall was built, although many structures have fallen into the ocean or have been demolished over the years. While in the immediate years after the war there was little interest in preserving these structures, there have been recent movements to preserve the remaining structures in order to preserve the memory of what existed during the war.

On March 23, 1942 Führer Directive Number 40 called for the official creation of the Atlantic Wall. After the St. Nazaire Raid, on April 13, 1942 Adolf Hitler ordered naval and submarine bases to be heavily defended. Fortifications remained concentrated around ports until late in 1943 when defences were increased in other areas.

Organisation Todt, which had designed the Siegfried Line (Westwall) along the Franco-German border, was the chief engineering group responsible for the design and construction of the wall's major fortifications. Thousands of forced laborers were impressed to construct these permanent fortifications along the Dutch, Belgian and French coasts facing the English Channel.

Early in 1944, Field Marshal Erwin Rommel was assigned to improve the Wall's defences. Rommel believed the existing coastal fortifications were entirely inadequate and he immediately began strengthening them. Under his direction, a string of reinforced concrete pillboxes was built along the beaches, or sometimes slightly inland, to house machine guns, antitank guns and light artillery. Mines and antitank obstacles were planted on the beaches themselves and underwater obstacles and mines were placed in waters just off shore. The intent was to destroy the Allied landing craft before they could unload.

By the time of the invasion, the Germans had laid almost six million mines in northern France. More gun emplacements and minefields extended inland, along roads leading away from the beaches. In likely landing spots for gliders and parachutists, the Germans emplaced slanted poles with sharpened tops, which the troops called Rommelspargel ("Rommel's asparagus"). Low-lying river and estuarine areas were permanently flooded, as well.

Rommel firmly believed that Germany would inevitably be defeated unless the invasion could be stopped at the beach.

Although the defensive wall was never completed, the Wall's existence has served to explain away concerns of the Soviet Union as to why the Second Front was not opened until June 6, 1944 (less than a year before the end of the war in Europe). The Wall primarily consisted of batteries, bunkers, and minefields, which during 1942–1944, stretched from the French-Spanish border to Norway (Festung Norwegen). Many bunkers still exist, for example near Scheveningen, Den Haag, Katwijk and in Normandy. In Oostende, Belgium the public may visit a well-preserved part of the defences. That section consists of emplacements of the "Saltzwedel neu battery" and the "Stützpunkt Bensberg", consisting of several men’s quarters and the necessary facilities. These constructions were used by a unit of German military engineers (Pionierstab) who were in charge of bunker construction.

The Channel Islands were heavily fortified, particularly the island of Alderney which is closest to Britain. Hitler had decreed that 1/12th of the steel and concrete used in the Atlantic Wall go to the Channel Islands, because of the propaganda value of controlling British territory. The Channel Islands were some of the most densely fortified areas in Europe with a host of Hohlgangsanlage tunnels, Casemates and Coastal artillery positions. Mountbatten commented: "Each island is a veritable fortress, the assault against which cannot be contemplated unless the defences are neutralised, or reduced to a very considerable extent by prior action." Despite the mooting of Operation Constellation et al., the Allies bypassed the islands and did not try to liberate them when they invaded Normandy. The islands' German garrisons did not surrender until 9 May 1945 – one day after the German armed forces on the mainland. The German garrison on Alderney did not surrender until 16 May. Because the German garrison surrendered peacefully the Channel Islands are host to some of the best preserved Atlantic Wall sites.

Walcheren Island was considered to be the "strongest concentration of defences the Nazis had ever constructed"... (see more at: http://en.wikipedia.org/) 

Nazi Mega Weapons

About The series.- In a quest for world domination, the Nazis built some of the biggest and deadliest pieces of military hardware and malevolent technology in history. The six-part series Nazi Mega Weapons recounts Germany’s engagement in World War II from a unique perspective, uncovering the engineering secrets of iconic megastructures, telling the stories of the engineers who designed them and revealing how these structures sparked a technological revolution that changed warfare forever.

With historic footage, recreations of milestone moments and interviews with history, engineering, and military strategy experts, Nazi Mega Weapons recounts the strategic triumphs and wartime blunders of the Third Reich.

“The scope of these projects and the superhuman efforts that brought them to fruition remains astonishing, even 70 years later,” said Executive Producer Simon Young, “We want viewers to understand the extraordinary lengths to which the Nazis went in order to realize their ill-fated dream of world domination. This was a fascinating era of history, made even more chilling by the fact that some many of these structures are still around today.” 

About Atlantic Wall.- To protect occupied Europe from an Allied invasion, Hitler demanded the construction of a defensive wall stretching thousands of kilometers from France in the south to Norway in the north. This is the story of how this vast engineering project sucked in huge quantities of raw materials and men from all over the Third Reich, and faced its ultimate test on D-Day.