On the defensive since July 1943 and facing a massive bombing campaign on its industries, Germany was counting on new weapons to regain an advantage and win battles. To strike Great Britain and force it to accept a peace deal, enabling German troups to concentrate on the Russian Front, the Reich counted on three Wunderwaffen (miracle weapons) to change the course of the war – V1 flying bomb, V2 ballistinc missile, and a long-range multi-charge cannon known as ‘Hochdruckpurge’ or V3.
The V3 was a cannon with a very long barrel and required the construction of gigantic underground structures, with the Mimoyecques site selected for the first of these due to distance from London - the untested range of the weapon was around 150km – and the location was out of range of attacks from Navy guns or Commando raids. Due to the depth of tunnelling needed, the geology had to be uniform to a depth of at least 100m too.
The multi-charge gun – also known as the ‘London Gun’ due to its main target - was created in 1942 by engineer August Coenders, an expert in special shells, who hoped to exceed the range of traditional guns by increasing the initial velocity of the proposed 15cm calibre, 230cm long projectile inside the barrel.

He calculated his ‘arrow-shell’ with fins would need a barrel of 127m and would be propelled via a series of charges along the barrel’s length - the projectile would have its trajectory accelerated by a successive detonation of additional cartridges inside chambers fitted in symmetrical pairs (there would be 32 in the final version) at each section of the gun.
The aim was to achieve a firing rate of 2.5 rounds per hour from each barrel – 50 barrels were planned - capable of striking the target with 3,000 rounds a day, meaning 90 tons of explosive would hit the streets of London.

The existence of abnormal activity in the ‘Marquise-Mimoyecques’ area was noticed on photographs taken on September 18, 1943. Here, digging to create access for two parallel railway tunnels could be distinguished. The first two bombing raids were carried out on the suspect site on November 5 and 8, 1943. While the destruction was very limited and did not affect the underground work, the site was still not ready for firing by the time Canadian forces captured the site in September 1944.
A survey of the site contained a recommendation to destroy Mimoyecques as an ‘absolute priority’ so it would never be operable again and in May 1945 British Royal Engineers placed 36 tons of TNT in 38 locations to block access to the tunnel systems while removing the huge steel sheets located on the surface of the hillside above.
These steel sheets were the openings to the gun barrels and can now be seen next to the entrance and car park at the site.
Some of the tunnels at the Mimoyecques V3 facility were opened up again and can now be visited – it’s quite an experience!