The 'Atlantikwall' was a very substantial German system of coastal defences and fortifications constructed between 1942 and 1944 along the coast of continental Europe and Scandinavia as a defence against an anticipated Allied invasion of German-occupied Europe from the UK (1942/May 1945).

The manning and operation of the 'Atlantikwall' was overseen administratively by the German army, with some support from Luftwaffe ground forces, while the German navy maintained a separate coastal defence network based on a number of sea defence zones.

Adolf Hitler ordered the construction of the fortifications in 1942 through his Führerweisung Nr 40, and more than half a million French workers were drafted to build it. The wall was frequently mentioned in German propaganda, in which its size and strength were usually exaggerated. The fortifications included colossal coastal guns, batteries, mortars and artillery, and thousands of German troops were stationed in its defences. Today, ruins of the wall exist in all the nations where it was built, although many structures have fallen into the ocean or have been demolished over the years.

World War II in Europe began on 1 September 1939, with Germany’s 'Weiss' (i) invasion of Poland. Two days later, the UK and France declared war on Germany. Poland’s geographical location, however, prevented the Allies from intervening directly, and after four weeks the Germans had occupied the western part of Poland, whose eastern part was overrun by the USSR. Less than a month after this victory, Hitler issued a directive stating that Germany must be ready to undertake an offensive through the Low Countries and France. The Oberkommando der Wehrmacht was convinced that preparations would last at least into the following year, however, and after furious argument Hitler reluctantly agreed to wait. In May 1940, three great German army groups overran the Low Countries and France in little more than six weeks.

Before the 'Atlantikwall' decision but after a number of British commando raids, on 2 June Hitler asked for maps of the Channel Islands. These were provided on the following day, and by 13 June Hitler had made a decision. Ordering additional men to the islands and having decided that the defences were inadequate, lacking tanks and coastal artillery, the Organisation 'Todt' construction organisation was ordered to undertake the building of some 200 to 250 strongpoints on each of the larger islands. The plan was finalised by the Organisation 'Todt' and submitted to Hitler. This original defence order was reinforced with a second on 20 October, following a Führer conference on 18 October to discuss the engineers' assessment of requirements. The permanent fortification of the Channel Islands was to make them into an impregnable fortress to be completed within 14 months, and the Festungspionierkommandeur XIV command was created to supervise the project of fortifying the Channel Islands.

It was six months later, on 23 March 1942, that Hitler issued his Führerweisung Nr 40 demanding the creation of an 'Atlantikwall'. Within this, he ordered that naval and U-boat bases were to be heavily defended. The fortification process thus remained concentrated around ports until a time late in 1943, when defences were increased in other areas. This decision required army engineers and the Organisation 'Todt' to plan and organise at high speed. Massive quantities of cement, reinforcing steel and armour plate would be required, and all of this would have to be transported to innumerable coastal defence sites.

German propaganda claimed that the wall extended from the the North Cape of Norway down to the Franco-Spanish border.

The Regelbau (standard build) system used books of plans for each of more than 600 approved types of bunker and casemate, each having a specific purpose. The various plans had been steadily updated as countries were overrun and their defensive works examined, some of them even being tested to destruction to prove their effectiveness. The works incorporated standard features, such as an entrance door at right angles to lines of approach, armoured air intakes, steel doors 1.2 in (30 mm) thick), ventilation and telephone systems, internal walls lined with wood, and an emergency exit system. There were more than 200 standardised armour parts.

The standardisation concept greatly simplified the manufacture of equipment, the supply of materials and the budgetary and financial control of the construction as well as the speed of planning for construction projects.

To offset shortages, captured equipment of the armies of France and other occupied countries was incorporated in the defences, casemates were designed for non-German artillery, anti-tank and machine guns, and the turrets of obsolete tanks were used in Tobrukstand pillboxes.

The Organisation 'Todt', created in 1933, had designed the 'Siegfried-Linie' defences during the pre-war years along the Franco-German border, and now became the chief engineering group responsible for the design and construction of the wall’s major gun emplacements and fortifications.

The Organisation 'Todt' supplied supervisors and labour as well as undertaking the organisation of supplies, machinery and transport to supplement the staff and equipment of other construction companies. Many of the latter were German, but construction companies in occupied counties also bid for contracts. Companies could apply for Organisation 'Todt' work or could be conscripted.  Companies failing to complete their work to schedule, which was always possible as the Organisation 'Todt' controlled the matériel and manpower of each firm, could find themselves closed down, though the levying of fines was more common, or taken over or merged with another firm to make a more efficient larger unit. Successful firms however could make healthy profits.

The Organisation 'Todt' obtained quotes for necessary works and signed contracts with each construction company, setting out the price and terms of the contract, such as bonus payments for efficiency, including the wage rates and bonus payments for Organisation 'Todt' workers based on their nationality and skills. There could be several construction companies working on each site.

The very large labour force comprised skilled volunteers, engineers, designers and supervisors, who were paid and treated well, in it first tier. Second came volunteer workers, often skilled technicians, such as carpenters, plumbers, electricians and metal workers who were also paid, took holidays and were well treated. Third came the unskilled forced labour, paid very little and treated quite harshly. Fourth came what was in effect slave labour, paid little, badly fed and treated very harshly. The Organisation 'Todt' ran training courses to improve the skill levels of the labour force.

Massive numbers of workers were needed. The Vichy French régime imposed a compulsory labour system, drafting some 600,000 French workers to construct the permanent fortifications along the Dutch, Belgian and French coasts on the southern side of the English Channel. The efficiency of the Organisation 'Todt' decreased late in 1943 and during 1944 as a result of manpower pressures, fuel shortages and the bombing of work sites such as V-weapons sites, where some volunteer workers refused to work in such dangerous conditions.

In January 1944, the Organisation 'Todt' group responsible for the Cherbourg area at the head of the Cotentin peninsula dealt with 34 companies with 15,000 workers, and 79 sub-contractors. Daily, weekly and monthly reports showing progress, work variations, material used, stocks of material, labour hours used per skill type, the weather, equipment inventory and quality, level of supervision, employee absences, staffing levels, deaths and problems experienced all had to be filed with the Organisation 'Todt'. 

Throughout most of 1942/43, the 'Atlantikwall' remained a relaxed front for the Axis troops manning it, with only two large-scale British attacks. 'Chariot', launched near St Nazaire in March 1942, destroyed German pumping machinery for, and severely damaged, the Normandy dry dock and installations. The second attack was the 'Jubilee' raid on Dieppe during August 1942 to test the German defences and provide combat experience for the Canadian troops used in the undertaking. The Germans were defeated at St Nazaire, but had little difficulty in repulsing the attack at Dieppe, where they inflicted heavy casualties. Although the Dieppe raid was a disaster for the Allies, it alarmed Hitler, who was sure an Allied invasion in the west would soon follow. After Dieppe, Hitler gave Generalfeldmarschall Gerd von Rundstedt, the Oberbefehlshaber 'West', 15 more divisions to bolster the German defence.

Early in 1944, with an Allied invasion of occupied Europe becoming ever more likely, Generalfeldmarschall Erwin Rommel was assigned to improve the wall’s defences. Believing the existing coastal fortifications to be entirely inadequate, Rommel launched an immediate programme to strengthen them. Rommel’s main concern was Allied air power, whose growth and capabilities he had experienced for himself when fighting the British and Americans in North Africa, and this had left a profound impression on him. He feared that any German counterattack would be broken up by Allied aircraft long before it could make a difference against a force that managed to make a landing. Under Rommel’s direction, hundreds of reinforced concrete pillboxes were built on the beaches, or sometimes slightly inland of them, to house machine guns, anti-tank guns, and light, medium and heavy artillery. Land mines and anti-tank obstacles were planted on the beaches, and underwater obstacles and naval mines were placed in waters just off likely landing beaches. Little known was that touch sensitive mines were placed atop the beach obstacles, and the overall intent was the destruction of Allied landing craft before they could unload onto the beaches.

By the time of the Allied invasion in June 1944, the Germans had laid almost six million mines in northern France. More gun emplacements and minefields extended along roads leading inland from the beaches. In areas in which gliders and paratroopers might land, the Germans planted slanted poles with sharpened tops, which the troops called Rommelspargel (Rommel’s asparagus). Low-lying river and estuarine areas were intentionally flooded. Rommel believed that Germany would inevitably be defeated unless the invasion could be stopped on the beach, declaring 'It is absolutely necessary that we push the British and Americans back from the beaches. Afterwards it will be too late; the first 24 hours of the invasion will be decisive.'

The Channel Islands were heavily fortified, none more so than the island of Alderney, which is closest to the UK. Hitler had decreed that one-twelfth of the steel and concrete used in the 'Atlantikwall' should go to the Channel Islands as he placed great emphasis on the propaganda value of controlling British territory. The islands were some of the most densely fortified areas in Europe, with a host of Hohlgangsanlage tunnels, casemates and coastal artillery positions.

However, as they lacked strategic significance, the Allies bypassed the Channel Islands when they invaded Normandy. As a result, the German garrisons stationed on the islands did not surrender until 9 May 1945, one day after VE-Day. The garrison on Alderney did not surrender until 16 May.

Many major ports and positions were incorporated into the 'Atlantikwall', and thus received heavy fortifications. Hitler ordered all positions to fight to the end, and some of them remained in German hands until Germany’s unconditional surrender. Several of the port fortresses were resupplied by U-boats after being surrounded by Allied ground forces.