The battery consisted of four Krupp 380-millimetre (15 in) guns with a range up to 55.7 kilometres (34.6 mi),[1] capable of reaching the British coast, each protected by a bunker of reinforced concrete.

Grand Admiral Erich Raeder met Hitler on 21 May 1940 and raised the topic of invasion, but warned of the risks and expressed a preference for blockade by air, submarines and raiders.

Over half of the Kriegsmarine surface fleet had been either sunk or badly damaged in Operation Weserübung, and his service was hopelessly outnumbered by the ships of the Royal Navy.

[8] The Kriegsmarine's Naval Operations Office deemed this a plausible and desirable goal, especially given the relatively short distance, 34 km (21 mi), between the French and English coasts.

Outside of firing periods, the guns and their accompanying carriages would find refuge in quarries, under the railway tunnels or under one of the three dombunkers (cathedral-bunkers), reinforced concrete shelters of an ogival shape whose construction began in September 1940.

The railway guns could be fired at shipping but were of limited effectiveness due to their slow traverse speed, long loading time and ammunition types.

The fortification of the Atlantic coast, with a special attention to ports, was accelerated in the aftermath the British amphibious attack on the heavily defended Normandie dry dock at St Nazaire during Operation Chariot on 28 March 1942.

[26]The battery fired its first shell on 20 January 1942, although it was only officially opened in February 1942 in the presence of Admirals Karl Dönitz and Erich Raeder.

[27][28] Originally to be called Siegfried Battery, it was renamed in honor of the German engineer Fritz Todt, creator of the Todt Organisation and responsible for the construction of the Atlantic Wall, who died on 8 February 1942 in a plane crash days before the battery's inauguration after meeting with Hitler at his Eastern Front military headquarters ("Wolf's Lair") near Rastenburg in East Prussia.

Winston Churchill, in his book "The Second World War", recorded that the British had already identified the Todt, Friedrich August, Grosser Kurfürst, Prinz Heinrich and Oldenburg batteries, together with fourteen other 17-cm guns, were "by the middle of September [1940] mounted and ready for use in this region alone", around Calais and Cape Gris-Nez.

[34][36] The Organisation Todt could also use a fully equipped sawmill in Outreau, south of Boulogne-sur-mer, to produce the large quantities of formwork needed for the reinforced concrete structures and to transport it to the construction site.

[22][34] The pivot of the armored turreted 38 cm SK C/34 naval gun was at the center of an open vast circular room with an internal diameter of 29 m, under an 11-meter high ceiling.

The railroad track connecting the casemate to the main ammunition bunkers located at Onglevert arrived at the level of the higher bench through two 2 meters-wide openings.

It established early 1940 several sea defense zones to protect the large amount of coastline which Germany had acquired after invading the Low Countries, Denmark, Norway, and France.

The command center, two personnel bunkers, a water reservoir with its close-combat defensive positions at Cran-aux-Oeufs formed the strongpoint Widerstandsnest (Wn) 166a Seydlitz.

[43] These units were capable of detecting targets out to a range of 40 km (25 mi), including small British patrol craft inshore of the English coast.

[45] As with other German large-caliber naval rifles, these guns were designed by Krupp and featured sliding-wedge breechblocks, which required brass cartridge cases for the propellant charges.

Plans were made to install two of these mounts at Cap de la Hague and two at Paimpol in France, modifying guns originally intended for an abortive refit of Gneisenau, but were not executed for unknown reasons.

These French guns were originally transported to Norway following the decision in March 1944 to install them, using the C/39 armored single mounts, in the Vardåsen coastal battery at Nøtterøy (M.K.B.

However, despite firing on frequent slow-moving coastal convoys, often in broad daylight, for almost the whole of that period (there was an interlude in 1943), there is no record of any vessel being hit by them, although one seaman was killed and others were injured by shell splinters from near misses.

[14] Following the victory of Operation Overlord and the break-out from Normandy, the Allies judged it essential to silence the German heavy coastal batteries around Calais which could threaten Boulogne-bound shipping and bombard Dover and inland targets.

[70] As part of Operation Undergo, the 3rd Canadian Infantry Division led the attack on the two heavy batteries at Cape Gris-Nez which threatened the sea approaches to Boulogne.

Preceded by local bombardments to keep the defenders under cover until too late to be effective, infantry assaults would follow, accompanied by flame-throwing Churchill Crocodiles to act as final "persuaders".

The concrete walls were impervious even to AVRE petard mortars but their noise and concussion, along with hand grenades thrown into embrasures, induced the German gunners to surrender by mid-morning.

[73][75][72][76][77][78] In August 1945, two French visitors accidentally triggered a massive explosion in Casemate 3, which pushed out part of the sidewall and caused the ceiling to collapse.

The agricultural parcels were delimited with dry stone walls and hedgerows separated the cultivated areas from the grassland used for the grazing of sheep and cows.

With the help of several people and after three years of work, the private museum about World War II, Musée du Mur de l'Atlantique, opened its doors in 1972.

An exterior metal staircase, later dismantled, replaced the old concrete one destroyed in 1944 that gave access to the roof, which was surrounded by a guardrail and open to the public.

[88][89] Outside the museum, one of two surviving German Krupp 28 cm K5 railway gun is displayed on an iron track, alongside military vehicles and tanks.

At the beginning of the 1980s, the existence of this 28 cm K5(E) Ausführung D (model D) cannon, originally stationed at Fort Nieulay (Stp 89 Fulda) in Calais, became known to the founder of the museum.