Fortress of Mimoyecques

The Fortress of Mimoyecques is the modern name for a Second World War bunker complex built by the forces of Nazi Germany between 1943 and 1944 to house a battery of V-3 cannons aimed at London, situated 165 kilometres (103 mi) away. Originally codenamed Wiese ("Meadow") or Bauvorhaben 711 ("Construction Project 711"),^[2] it is located in the commune of Landrethun-le-Nord in the Pas-de-Calais region of northern France, about 20 kilometres (12 mi) from Boulogne-sur-Mer.

The complex consists of a network of tunnels dug under a chalk hill, linked to five inclined shafts in which fifty V-3 guns would have been installed, all of them targeted on London. The weapons would have been able to fire ten shells a minute – 600 tons of shells an hour – into London, a threat that Winston Churchill later described as potentially "the most devastating attack of all on London." The Allies knew nothing about the V-3 but identified the site as a possible launching base for V-2 ballistic missiles. It was thus targeted for intensive bombardment by the Allied air forces from late 1943 onwards. It was put out of commission on 6 July 1944 by 617 Squadron RAF using 5,400-kilogram (12,000 lb) "Tallboy" earthquake bombs. Never formally abandoned, the complex was overrun on 5 September 1944 by the Canadian 3rd Infantry Division.^[2]

The complex was partly demolished just after the war on Churchill's direct orders, as it was seen to still be a threat to the United Kingdom. It was later reopened, first as a mushroom farm in 1969 and subsequently as a museum in 1984. It was acquired by a nature conservation organisation in 2010 and reopened under the management of the museum of La Coupole, a former V-2 rocket base near Saint-Omer.^[3]

Background

The origin of the multi-chamber gun dates back from the 19th century. In 1857 U.S. arms expert Azel Storrs Lyman (1815–1885) was granted a patent on "Improvement in accelerating fire-arms" ^[4] and built in 1860 a prototype which proved to be unsuccessful.^[5][6] The idea was perfected in collaboration with James Richard Haskell that had been working for years on the same principle^[7][8] Haskell and Lyman reasoned that subsidiary propellant charges, spaced at intervals up the barrel of a gun in side chambers and ignited an instant after a shell had passed them, could increase the muzzle velocity of a projectile. The "Lyman-Haskell multi-charge gun", constructed on the instructions of the US Army's Chief of Ordnance, did not resemble a conventional artillery piece. The barrel was so long that it had to be laid on an inclined ramp, and it had pairs of chambers angled back at 45 degrees let into it. It was test fired at the Frankfort Arsenal at Philadelphia in 1880 and was proven unsuccessful. Due to faulty obturation, the flash from the original propellant charge bypassed the projectile and prematurely ignited the subsidiary charges before the shell passed them, slowing the shell down.^[9][10] The best velocity that could be obtained from it was 335 metres per second (1,100 ft/s), inferior to the performance of a conventional RBL 7 inch Armstrong gun of the same period.^[11] Although new prototypes of multi-charge guns were built and tested,^[12][13] Lyman and Haskell abandoned the idea.^[6][14]

During the same period, a French engineer Louis-Guillaume Perreaux, one of the pioneers of motorcycle, had been working on a similar project since before 1860.^[17] Perreaux was granted a patent in 1864 for a multi-chamber gun.^[18] In 1878 Perreaux presented his invention at the World Exhibition of Paris.^[19] In 1918 the French Army made plans for very long range multi-chamber gun in response to the German Paris Gun.^{[notes 1]} This Krupp gun could bombard Paris from German lines over a distance of no less than 125 kilometres (78 mi). However, the French initiative did not reach the prototype stage because the retreat of the German armies and the armistice put an end to the bombardment. The plans for the multi-chamber gun envisaged to counter the German fire were archived.^[20]

Twenty years later, when France collapsed in June 1940 at the beginning of World War II, the German troops got their hands on the plans of this long-range gun.^[5] In 1942, this patent attracted the attention of August Coenders,^{[notes 2]} developer of the Röchling shell and chief engineer of the plants "Röchling Stahlwerk AG" in Wetzlar, Germany. Coenders thought that the gradual acceleration of the shell by a series of small charges spread over the length of the barrel may be the solution to the problem of designing very long range guns. The very strong explosive charge needed to project the shells at high speed were causing very rapid degradation of the gun tube. ^{[notes 3]} Coenders proposed the use of electrically activated charges to eliminate the problem of the premature ignition of the subsidiary charges experienced by the Lyman-Haskell gun. Coenders built a prototype of a 20 mm multi-chamber gun using the machinery readily available at the Wetzlar plant that was producing tubes of this caliber for the Flak 38 anti-aircraft guns of 20 mm.^[5] The first tests were encouraging but to get the support of the Ministry of arms Hermann Röchling had to present to Albert Speer Coenders' project of a cannon capable of firing on London from the coast of the Pas-de-Calais. Two batteries could crush London under a barrage of hundreds of shells per hour, shells of 140 kilograms (310 lb) with an explosive charge of 25 kilograms (55 lb).

In May 1943, Albert Speer, the Reich Minister of Armaments and War Production, informed Adolf Hitler of work that was being carried out to produce a supergun 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 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 previous ones, such as Schwerer Gustav and the Paris gun, were limited by the short life of the barrels caused by high-pressure detonations. The HDP, by contrast, would have a smooth barrel over 100 metres (330 ft) long along which a 97 kilograms (210 lb) finned shell (known as the Sprenggranate 4481) would be accelerated by numerous small charges fired electrically in sequence in branches off the barrel.^[21]

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.^[22] Speer noted afterwards:

On my suggestion, the Führer has decided that the risk must be stood to award contracts at once for the “high-pressure pump,” without waiting for the results of firing trials. Maximum support is to be accorded to the experimental ranges at Hillersleben and Misdroy, and especially to the completion of the actual battery.^[23]

The weapon's great length, with barrels 127 metres (417 ft) long required to attain a range necessary to reach England, meant that it could not be moved; it would have to be deployed from a fixed site.^[24] 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.^[25]

The site was chosen by a fortification expert, Major Bock of the Festung Pioneer-Stab 27^{[notes 4]} of the Fifteenth Army LVII Corps based in the Dieppe area.^[26] A limestone hill near the hamlet of Mimoyecques, 158 metres (518 ft) high and 165 kilometres (103 mi) from London, was chosen to house the gun. It had been chosen with care; the hill is primarily chalk with very little topsoil cover and the chalk layer extends several hundred metres below the surface of the ground, providing a deep but easily tunnelled rock layer in which the facility could be built. The chalk is easy to excavate and strong enough for tunnels to not require timber supports. Although the site's road links are poor, it is just to the west of the main railway line between Calais and Boulogne-sur-Mer.^[27] The area was already heavily militarised; as well as the fortifications of the Atlantic Wall on the cliffs of Cap Gris Nez to the north-west, there was a firing base for at least one^[28] conventional Krupp K5 railway gun about 5 kilometres (3.1 mi) to the south in the nearby quarries of Hidrequent-Rixent.^{[29][notes 5][notes 6]}

Design and construction

The construction work 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 1,000 metres (3,300 ft) 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 normal guns; the entire battery would be able to fire 10 shots a minute, putting 600 tons of shells on London each day. Both facilities were to be served by an underground railway tunnel of standard gauge,^{[notes 7]} connected to the Calais-Boulogne main line,^{[notes 8]} and underground ammunition storage galleries which were tunneled at a depth of about 33 metres (108 ft). However, only the eastern site was built after construction of the western site was disrupted by Allied bombing.^[2][30]

The drifts were angled at 50 degrees, reaching a depth of 105 metres (344 ft). Due to technical problems with the gun prototype, the scope of the project was reduced;^[25] 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 30 metres (98 ft) wide and 5.5 metres (18 ft) 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.^[31] Each drift was oriented on a bearing of 299° ± 30 minutes – 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 – thereby enabling coverage of much of London.^[32]

The railway tunnel ran in a straight line for a distance of about 630 metres (2,070 ft). 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 24 metres (79 ft). Each gallery was fitted with a 60 cm (24 in) gauge Decauville light railway track. On the east side of the tunnel were a number of 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, which would have been used to supply the guns.^[33]

The central group of galleries, 6-10, gave access to the guns, while galleries 3-5 and 11-13 were intended for use as access tunnels and perhaps also storage areas. All of the galleries were connected by another gallery, known as Gallery No. 2, which ran parallel to the main railway tunnel at a distance of 100 metres (330 ft). Galleries 6-10 were additionally connected by a second passageway, designated Gallery No. 1, running parallel to the main tunnel at a distance of 24.5 metres (80 ft).^[33]

Further workings existed at depths of 62 metres (203 ft), 47 metres (154 ft) and 30 metres (98 ft), 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.^[31] The lower levels of the workings were accessed via lift shafts, with mining cages used during construction.^[32]

The construction work was carried out by over 5,000 workers, mostly German engineers drafted in from several companies including Mannesmann, Gute-Hoffnungs-Hutte, Krupp and United Steel, supplemented by 430 miners recruited from the Ruhr and Soviet prisoners of war used as slave labourers. The project faced delays caused by Allied bombing, and its cost virtually doubled when the facility's commandant insisted that the workings be extended to include underground living quarters, kitchens, power plants, ventilators and other ancillary installations. Further delays were caused by problems with the projectiles to be used in the gun tubes; it was estimated in May 1944 that the project had fallen six months behind schedule as a result.^[23]

Despite the problems, work continued at a high pace. 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.^[25] A report written on 2 June stated that the installation of the first five HDP barrels would begin on 15 July and would be completed by 15 August, with the second group of five barrels to be installed by September 15 and the third by October 15. In July 1944, a senior engineer working for the Reich Research Council reported that the facility was ready for the installation of the gun barrels but that it would be between four and nine months before the completion of the lining of the chalk tunnels with concrete. Over a thousand tons of steelwork had been delivered and was in the process of being installed, including the framework for the barrels and the breech chambers, the ammunition hoists, winches and winding drums, and the bombproof steel doors for the railway access tunnels. However, progress was hindered when the Allies managed to destroy the regional electricity grid following the D-Day landings.^[23]

Discovery and destruction

In 1943 French agents reported that the Germans were planning to mount an offensive against the United Kingdom that would involve the use of secret weapons resembling giant mortars sunk in the ground that would be served by rail links.^[34] The first signs of abnormal activity at Mimoyecques were spotted by analysts at the Allied Central Interpretation Unit in September 1943, when the Germans were observed building railway loops leading to the tunnels into the eastern and western sites. In October 1943, reconnaissance flights photographed continued activity with shafts being dug into the hilltop.^[27] The purpose of the site was unclear, but it was thought to be some kind of shelter for the launching of rockets or flying bombs. An assessment for the Ministry of Supply suggested that it might house two to four "rocket projectors", while other experts thought it might house a "mortar tube" to fire 50-60 ton rockets at London.^[23] An MI6 agent reported that "a concrete chamber was to be built near one of the tunnels for the installation of a tube, 40 to 50 metres long, which he referred to as a 'rocket launching cannon'". The Allies were totally unaware of the HDP gun; it was believed at the time that the A-4 rocket (later better known as the V-2) had to be launched from tubes or "projectors", so it was naturally believed that the inclined shafts at Mimoyecques were intended to house such devices.^[35]

The lack of intelligence on Mimoyecques was frustrating for those involved in Operation Crossbow, the Allied effort to counter the V-weapons. On 21 March 1944 the British Chiefs of Staff discussed the shortage of intelligence but were told by Reginald Victor Jones, one of the "Crossbow Committee" members, that little information was leaking out because the workforce was predominantly German. The Committee's head, Duncan Sandys, pressed for greater efforts and proposed that the Special Operations Executive be tasked to kidnap a German technician who could be interrogated for information. Although the suggestion was approved it was never put into effect. In the end the Chiefs of Staff instructed General Eisenhower to begin intensive attacks on the so-called "Heavy Crossbow" sites, including Mimoyecques.^[35]

The Allied air forces carried out several bombing raids on the Mimoyecques site between November 1943–June 1944 but caused little damage. On 6 July 1944, however, the Royal Air Force began bombing the site with the ground-penetrating Tallboy bomb for the first time. One Tallboy hit the concrete slab on top of Drift IV, collapsing the drift. Three others penetrated the tunnels below and caused substantial damage, causing several of the galleries to collapse in places.^[24] Some 300 Germans and workers were buried alive by the collapses.^[36] The Reich Research Council engineer who visited the site in July 1944 concluded that the facility could not survive such attacks: "the installations were not designed to withstand bombs such as these."^[23]

The devastating raid of 6 July led to the Germans holding a high-level meeting on the site's future at which Hitler ordered major changes to the site's development. On 12 July 1944 he signed an order instructing that only five HDP guns were to be installed in a single drift. The two others were to be reused to house a pair of Krupp K5 artillery pieces, reamed out to a smooth bore with a diameter of 310 millimetres (12 in), which were to use a new type of long-range rocket-propelled shell. A pair of Rheinbote missile launchers were to be installed at the tunnel entrances. However, these plans were soon abandoned as Allied ground forces advanced towards Mimoyecques and on 30 July the Organisation Todt engineers were ordered to end construction work.^[37]

The Allies were unaware of this and mounted further attacks on the site as part of the United States Army Air Force's experimental Operation Aphrodite, involving radio-controlled B-24 Liberators packed with explosives. Two such attacks were mounted but were failures; in the second such attack, on 12 August, Lt Joseph P. Kennedy, Jr. – the elder brother of future US President John F. Kennedy – was killed when the drone aircraft exploded prematurely.^[36]

The Mimoyecques site was never formally abandoned but German forces left it at the start of September 1944 as the Allies advanced north-east from Normandy towards the Pas-de-Calais. It was captured on 5 September by the Canadian 3rd Infantry Division.^[25]

Subsequent investigations and demolition

Shortly after the Wizernes site had been captured in September 1944, Duncan Sandys, the head of the British "Crossbow Committee", ordered the constitution of a Technical Inter-Services Mission under Colonel T.R.B. Sanders. It was given the task of investigating the sites at Mimoyecques, Siracourt, Watten, and Wizernes, collectively known to the Allies as the "Heavy Crossbow" sites. Sanders' report was submitted to the War Cabinet on 19 March 1945.^[38] The site was also visited by many other Allied scientists and engineers, including the Tallboy's designer Barnes Wallis, who had a keen interest in seeing how his bombs had performed.^[23]

Even at this stage the true purpose of the site was unclear. There were claims that it had been intended to be used for "electro-magnetic projectors" (railguns) firing huge shells at London, but these were debunked by Lord Cherwell, Winston Churchill's scientific adviser, who calculated that it would take sixty times the output of Battersea Power Station to fire a one-ton shell. Sanders' investigation brought to light the V-3 project for the first time, to the alarm of the British government. He concluded that although the site had been damaged it "could be completed or adapted for offensive action against this country at some future date, and [its] destruction is a matter of importance."^[23] Sandys brought the matter to the attention of Churchill and advised: "Since this installation constitutes a potential threat to London, it would be wise to ensure that it is demolished whilst our forces are still in France."^[38] Churchill later commented that the V-3 installation at Mimoyecques "might well have launched the most devastating attack of all on London."^[23][39]

The Chiefs of Staff recommended following the delivery of the Sanders report that the site should be demolished by the Royal Engineers. However, the French proved reluctant to acquiesce; Churchill was advised on 25 April that it was "very unlikely that the French will ever agree to the destruction of these installations, and unilateral action becomes more difficult with every day that passes." Churchill agreed and on 30 April told SHAEF: "It would be intolerable if the French insisted on maintaining installations directly menacing our safety after we have shed so much blood in the liberation of their country." On 9 May the Royal Engineers stacked ten tons of British 500 lb (230 kg) bombs and captured German plastic explosive in the tunnels at Mimoyecques and detonated it. This failed to achieve the desired effect and on 14 May, a further 25 tons of explosives were used to bring down the north and south entrances to the railway tunnel into the site. A subsequent investigation by the British Bombing Research Mission concluded that the entrances had been heavily blocked and that it would be a very difficult and lengthy engineering task to reinstate them.^[21][23]

Reopening as a museum

After the war, the Mimoyecques site lay abandoned. Much of the equipment left by the Germans was disposed of as scrap metal. A complete set of 4 armor steel plates^[28] – weighing 60 tons – that were intended to protect the entrances to the drifts were bought by the manager of the Hidrequent-Rixent quarries to be cut up for use in rock-crushing machinery.^[21] Rediscovered by local historians in the 1990s,^[28] they remained at the quarries until 2010, when the surviving plates returned to Mimoyecques and are now on display there.^[40]

Despite the closure of the railway tunnel entrances it was nonetheless still possible for many years to get into the complex by climbing down one of the inclined drifts.^[21] In 1969, Marie-Madeilene Vasseur, a farmer of Landrethun, had the southern entrance excavated so that the tunnels could be reused as a mushroom farm.^[41] Some 30 metres (98 ft) of the southern tunnel had to be removed to clear the blockage; the entrance now visible is not the original one built by the Germans.^[42] The southern entrance was bricked up again by the 1970s.^[21] Moved to discover this forgotten construction, Vasseur, helped by family and friends, cleared the tunnels and installed an electricity supply. The société à responsabilité limitée "La Forteresse de Mimoyecques" was constituted in 1984 to operate the site as a museum under the name of Forteresse de Mimoyecques — Un Mémorial International.^[43] The museum closed at the end of the 2008 season when the owner decided to retire. Subsequently, the nonprofit organization Conservatoire d'espaces naturels du Nord et Pas-de-Calais ^[44](Conservatory of natural sites of the Nord and Pas-de-Calais) purchased it at a cost of €330,000, with funding provided by the Nord-Pas-de-Calais regional council, the European Union and a private benefactor.^[45] The Conservatory's interest was due to the presence on the site of a large bat colony^[46] that included a number of rare species, including the Greater Horseshoe Bat, Geoffroy's Bat and the Pond Bat.^[47][48]

The intercommunality of the Terre des Deux Caps and the authorities in nearly Landrethun set up a partnership to operate the site under the management of the existing museum of La Coupole near Saint-Omer. The director of the latter, historian Yves le Maner, designed the contents of a new museum that was constructed at a cost of €360,000.^[45] The site reopened to the public on 1 July 2010.^[40] As well as presenting a history of the V-weapons and of the site, the museum enables visitors to see a number of the tunnels as well as a mock-up of the HDP gun and memorials to Lt Joseph Kennedy, the other bomber crew members killed during raids on the site and the forced labourers who lost their lives during the construction works.^[42] From July to September 2010, the museum welcomed 6,004 visitors, of which 55% were French, 18% Belgian and 16% British.^[49]

Air raids on the Mimoyecques site

Notes

References

Bibliography

External links

• Fortress of Mimoyecques - museum website
• (French) Une base pour bombarder Londres
• (French) Chroniques Historiques - Les tunnels de Mimoyecques: la Base V3
• (French) Forteresse de Mimoyecques - Quand histoire et nature ne font qu'un