The Atlantic Wall (German: Atlantikwall) was an extensive system of Coastal fortifications built by Nazi Germany between 1942 and 1944 along the western coast of Europe as a defense against an anticipated Allied invasion of the mainland continent from Great Britain.

Construction 
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 began strengthening them.  He knew that the beaches between were barely defended, and the Allies could land there and capture the ports from the land.  Under his direction, a string of reinforced concrete pillboxes were built along the beaches, or sometimes slightly inland, to house machine guns, anti-tank 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.

The Germans 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 military gliders and paratroopers, the Germans installed slanted poles with sharpened tops, which the troops called Rommelspargel ("Rommel's asparagus").  Low-lying land near rivers was 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 was used to address concerns of the Soviet Union for why the Second Front was not opened until June 6, 1944 (less than a year before the end of the war).  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 England (Jersey being the closest to France).  Hitler had decreed that one twelfth of the steel and concrete used in the Atlantic Wall go to the Channel Islands, because they were British territory.  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.

Walcheren Island was considered to be the "strongest concentration of defences the Nazis had ever constructed."

Atlantic Wall Commands
The Atlantic Wall was not a single organisation except in the administration of its building. Militarily it was divided into eight commands:
 Norway Army Command
 Forces Commander in Danmark
 Deutschen Bucht Command
 Wehrmacht Netherlands Command
 Armee Oberkommando 15 (15th Army zone)
 Armee Oberkommando 7 (7th Army zone)
 Armee Oberkommando 1 (1st Army zone)
 Armee Oberkommando 19 (19th Army zone)

Atlantic Wall Fortresses
Many major ports and positions were made part of the Atlantic wall and received heavy fortifications, Hitler ordered them all to fight to the end  and some of them remained in German hands until the unconditional surrender of Axis Forces on May 8, 1945. Several of the port fortresses were resupplied by submarine after being surrounded by Allied forces. The defenders of these positions included Slavic soldiers and SS troops.

References 

German Publication (PhD) in military history
Dr. Thorsten Heber: Der Atlantikwall 1940–1945. Band I Die Befestigung der Küsten West- und Nordeuropas im Spannungsfeld nationalsozialistischer Kriegführung und Ideologie. 564 Seiten, 157 Bildtafeln mit 535 Abb. BoD 2008, .
Dr. Thorsten Heber: Der Atlantikwall 1940–1945. Band II Die Invasion – Die Atlantikfestungen 1944/45 – Der Atlantikwall in Deutschland, Dänemark, Norwegen – Kompendium Regelbauten. 504 Seiten, 196 Bildtafeln mit 670 Abb. BoD 2008, .

Further reading 
Kauffmann, J.E. and Jurga, Robert M. Fortress Europe: European Fortifications of World War II, Da Capo Press, 2002.

Other websites 

 AtlantikWall.co.uk
 AtlantikWall.dk
 The defences of the Atlantikwall at Omaha Beach 
 Atlantikwall.fr
 Atlantikwall.net 
 The Atlantikwall in Denmark
 Bunkertypes, maps, museums and others
 The Atlantic Wall Linear Museum 
 Britannica Online
 Museumscenter Hanstholm
 Kristiansand Cannon Museum 
 Vara Battery (Kristiansand, Norway)
 Fortress Alderney 
 Information site about the Atlantikwall in the Netherlands, Haagse Bunker Ploeg
 Atlantikwall Museum Noordwijk, Site about the Atlantikwall Museum Noordwijk in the Netherlands
 Information about the open air museum in Ostend, Belgium. 
 Festung Europa : Bunkers in the Atlantikwall
 Places of interest for the war tourist along Hitlers Atlantic Wall in Denmark and Norway (English)
 Fortifications in Denmark and Europe through a thousand years (Danish)
 The Atlantic Wall in North Brittany (Bretagne Nord), France. Shore & Beach, 2004, 72:4 10–12

Alderney
Fortifications of World War II