The Fortress of Mimoyecques () is the modern name for a Second World War underground military complex built by the forces of Nazi Germany between 1943 and 1944. It was intended to house a battery of fixed V-3 cannons permanently aimed at London, away. Originally codenamed Wiese ("Meadow") or Bauvorhaben 711 ("Construction Project 711"), it is located in the commune of Landrethun-le-Nord in the Pas-de-Calais department of northern France, near the hamlet of Mimoyecques about from Boulogne-sur-Mer. It was constructed by a mostly German workforce recruited from major engineering and mining concerns, augmented by prisoner-of-war slave labour.
The complex consists of a network of tunnels dug under a chalk hill, linked to five inclined shafts in which 25 V-3 guns would have been installed, all aimed at London. The guns would have been able to fire ten dart-like explosive projectiles a minute – 600 rounds every hour – into the British capital, which Winston Churchill later commented would have constituted "the most devastating attack of all". The Allies knew nothing about the V-3 but identified the site as a possible launching base for V-2 ballistic missiles, based on reconnaissance photographs and fragmentary intelligence from French sources.
Mimoyecques was targeted for intensive bombardment by the Allied air forces from late 1943 onwards. Construction work was seriously disrupted, forcing the Germans to abandon work on part of the complex. The rest was partly destroyed on 6 July 1944 by No. 617 Squadron RAF, who used ground-penetrating "Tallboy" earthquake bombs to collapse tunnels and shafts. This also entombed hundreds of slave workers underground. Though attempts were made to continue construction, the Germans soon halted work at Mimoyecques entirely as the Allies advanced up the coast following the Normandy landings. It fell to the Canadian 3rd Infantry Division on 5 September 1944 without resistance, a few days after the Germans withdrew from the area.
The complex was partly demolished just after the war on Churchill's direct orders (and to the great annoyance of the French, who were not consulted), as it was still seen as a threat to the United Kingdom. It was later reopened by private owners, first in 1969 to serve as a mushroom farm and subsequently as a museum in 1984. A nature conservation organisation acquired the Fortress of Mimoyecques in 2010, and La Coupole, a museum near Saint-Omer housing a former V-2 rocket base, took over its management. It continues to be open to the public as a vast underground museum complex.
Background
In May 1943 Albert Speer, the Reich's Minister of Armaments and War Production, informed Adolf Hitler of work that was being carried out to produce a large-calibre gun capable of firing hundreds of shells an hour over long distances. The newly designed gun, codenamed the Hochdruckpumpe ("High Pressure Pump", HDP for short) and later designated as the V-3, was one of the V-weapons – Vergeltungswaffen ("retaliation or vengeance weapons") – developed by Nazi Germany in the later stages of the war to attack Allied targets.
Long-range guns were not a new development, but the high-pressure detonations used to fire shells from previous such weapons, including the Paris gun, rapidly wore out their barrels.
In 1942, August Coenders, inspired by previous designs of multi-chamber guns, suggested that the gradual acceleration of the shell by a series of small charges spread over the length of the barrel might be the solution to the problem of designing very long-range guns. Coenders proposed the use of electrically activated charges to eliminate the problem of the premature ignition of the subsidiary charges experienced by previous multi-chamber guns.
The HDP would have a smooth barrel over long, along which a finned shell (known as the Sprenggranate 4481) would be accelerated by numerous small low-pressure detonations from charges in branches off the barrel, each fired electrically in sequence.. Each barrel would be in diameter.
The gun was still in its prototype stages, but Hitler was an enthusiastic supporter of the idea and ordered that maximum support be given to its development and deployment. In August 1943 he approved the construction of a battery of HDP guns in France to supplement the planned V-1 and V-2 missile campaigns against London and the south-east of England.. Speer noted afterwards:
To reach England, the weapon needed barrels long, so it could not be moved; it would have to be deployed from a fixed site.. A study carried out in early 1943 had shown that the optimal location for its deployment would be within a hill with a rock core into which inclined drifts could be tunneled to support the barrels..
The site was identified by a fortification expert, Major Bock of the Festungs-Pionier-Stab 27Literal translation "Fortress Pioneer Staff" of the Fifteenth Army LVII Corps based in the Dieppe area.. A limestone hill near the hamlet of Mimoyecques, high and from London, was chosen to house the gun. It had been selected with care; the hill in which the facility was built is primarily chalk with very little topsoil cover, and the chalk layer extends several hundred metres below the surface, providing a deep but easily tunnelled rock layer. The chalk is easy to excavate and strong enough to dig tunnels without using timber supports. Although the site's road links were poor, it was only a few kilometres west of the main railway line between Calais and Boulogne-sur-Mer..
The area was already heavily militarised; as well as the fortifications of the Atlantic Wall on the cliffs of Cap Gris Nez to the northwest, there was a firing base for at least one conventional Krupp K5 railway gun about to the south in the nearby quarries of Hidrequent-Rinxent..
Design and construction Construction began in September 1943 with the building of railway lines to support the work, and excavation of the gun shafts began in October. The initial layout comprised two parallel complexes approximately apart, each with five drifts which were to hold a stacked cluster of five HDP gun tubes, for a total of 25 guns. The smoothbore design of the HDP would enable a much higher rate of fire than was possible with conventional guns. The entire battery would be able to fire up to 10 shots a minute, capable in theory of hitting London with 600 projectiles every hour. Both facilities were to be served by an underground railway tunnel of standard gauge,North entrance of railway tunnel: . South exit: connected to the Calais–Boulogne main line,The branch line to Mimoyecques connected with the main line here: and underground ammunition storage galleries which were tunneled at a depth of about . The western site was abandoned at an early stage after being disrupted by Allied bombing, and only the eastern complex was built..
The drifts were angled at 50 degrees, reaching a depth of . Owing to technical problems with the gun prototype, the scope of the project was reduced; drifts I and II were abandoned at an early date and only III, IV and V were taken forward. They came to the surface at a concrete slab or Platte wide and thick, in which there were narrow openings to allow the projectiles to pass through. The openings in the slab were protected by large steel plates, and the railway tunnel entrances were further protected by armoured steel doors.. Each drift was oriented on a bearing of 299°, to the nearest degree – a direct line on Westminster Bridge. Although the elevation and direction of the guns could not be changed, it would have been possible to alter the range by varying the amount of propellant used in each shot. This would have brought much of London within range.
The railway tunnel ran in a straight line for a distance of about . Along its west side was an unloading platform which gave access to ten cross galleries (numbered 3–13 by the Germans), driven at right angles to the main tunnel at intervals of . Each gallery was fitted with a gauge railway track. On the east side of the tunnel were chambers intended to be used as store rooms, offices and quarters for the garrison. Trains would have entered the facility and unloaded shells and propellant for the guns..
Galleries 6–10, the central group, gave access to the guns, while galleries 3–5 and 11–13 were intended for use as access tunnels and perhaps also storage areas. They were all connected by Gallery No. 2, which ran parallel to the main railway tunnel at a distance of . Galleries 6–10 were additionally connected by a second passageway, designated Gallery No. 1, running parallel to the main tunnel at a distance of . Further workings existed at depths of , and , each serving different purposes associated with the drifts and the guns. The 62 m workings were constructed to facilitate the removal of spoil from the drifts, while those at 47 m were connected with the handling of exhaust gases from the guns and those at 30 m gave access to the breeches of the guns. The lower levels of the workings were accessed via lift shafts, and mining cages were used during construction..
The construction work was carried out by over 5,000 workers, mostly German engineers drafted in from several companies including Mannesmann, Gute Hoffnungshütte, Krupp and the Vereinigte Stahlwerke, supplemented by 430 miners recruited from the Ruhr and Soviet prisoners of war who were used as slave labourers.. The intensive Allied bombing campaign caused delays, but construction work continued nonetheless at a high pace underground. The original plans had envisaged having the first battery of five guns ready by March 1944 and the full complement of 25 guns by 1 October 1944, but these target dates were not met.
Air raids