German heavy coastal artillery of the Atlantikwall preparing to fire

German heavy coastal artillery of the Atlantikwall preparing to fire. The successful German offensive in May and June 1940 placed Calais and its environs under the control of an enemy of the United Kingdom for the first time since the end of the Napoleonic Wars, 125 years earlier. In the initial directive for the invasion of the United Kingdom, codenamed Operation Sealion, which was issued on 2 July 1940 by the Oberkommando der Wehrmacht, the supreme command of the German armed forces, the requirement was stated for powerful coastal artillery to "provide additional cover... against English naval attack". In a further directive on 10 July, the purpose of the guns was stated to be "for covering the front and flanks of a future crossing and landing" and they were placed under the overall control of Erich Raeder, the Commander-in-Chief of the Kriegsmarine. Work to assemble and begin emplacing every Army and Navy heavy artillery piece available, primarily at Pas-de-Calais, commenced on 22 July 1940. The heavy construction work was undertaken by the Organisation Todt. The first such guns to be put in place were Wehrmacht guns on the French coast, which began to be installed around the end of 1940. First came Siegfried Battery at Audinghen, south of Cap Gris Nez, with one 38 cm (15 in) gun (later increased to 4 and renamed Todt Battery), shortly followed by: Three 30.5 cm (12 in) guns at Friedrich August Battery, to the north of Boulogne-sur-Mer; Four 28 cm (11 in) guns at Grosser Kurfürst Battery at Cap Gris Nez; Two 21 cm (8.3 in) guns at Prinz Heinrich Battery just outside Calais; Two 21 cm (8.3 in) guns at Oldenburg Battery in Calais; Three 40.6 cm (16 in) guns (from among the so-called Adolf Guns) at Lindemann Battery between Calais and Cap Blanc Nez (the battery was named after the fallen commander of the battleship Bismarck, Kapitän zur See Ernst Lindemann)

Sources :
https://en.wikipedia.org/wiki/Cross-Channel_guns_in_the_Second_World_War
https://www.pinterest.com/danielesorgato/artiglieria/