In May of 1943, Albert Speer, the Reich Minister for Armaments and War Production, informed Hitler that work had begun on new super guns, capable of firing hundreds of rounds an hour over an extremely long distance. An underground complex was dug in the Pas de Calais in northern France, across the narrowest stretch of the English Channel separating Nazi occupied Europe from England, to house the Vergetlungswaffe 3 (“Vengeance Weapon 3”). The super guns, whose name was shortened to the V-3 Cannon, were to be aimed at London, which the Nazis hoped to destroy.
The underground V-3 complex was to include over 165 kilometers of tunnels, dug by German workers and slave laborers. The network of tunnels was to be linked to 5 inclined shafts, in which 25 huge gun tubes were to be laid, all aimed at central London. As designed, the V-3s were to fire 10 explosive projectiles a minute, 600 rounds per hour, 24 hours a day, raining devastation down upon and wrecking London. As Winston Churchill later commented, if the Nazis had managed to pull it off, it would have been history’s most destructive conventional attack ever launched against a city.
The Allies were completely in the dark about the V-3 program. Reconnaissance flights did spot the activity surrounding the Pas de Calais complex, but analysts assumed the photos depicted a potential launching base for the V-2 rockets. V-2s were worrisome in of themselves, however, so the site was subjected to frequent Allied bombing from late 1943 onwards.
The raids seriously disrupted construction, and forced the Germans to abandon parts of the complex. The remainder of the site was seriously damaged in July of 1944, in a raid that used heavy ground penetrating bombs, which burrowed deep beneath the surface before detonating. The underground explosions wrecked and collapsed the tunnel system, and buried hundreds of workers and technicians. Construction was halted as the Allies advanced up the coast from Normandy to the Pas de Calais, and the abandoned V-3 complex fell to advancing Canadian troops in September of 1944. It was only then that the Allies discovered just how big a threat the complex had actually posed, and just how lucky London had been to dodge that menace.