Kraftwerk Nordwest KNW -
Mannschaftsbunker
The Blockhaus at Eperlecques
This amazing
complex is located in the Foret d’Eperlecques (Eperlecques
Forest) about 5 km. from Watten (A26 road Calais-Saint Omer),
France. This enormous bunker was constructed by the Germans in 1943 to
accommodate; V-2 reception and storage; preparation of rockets for launch
in a sheltered and controlled manner; on site production of liquid oxygen;
and launch control with two firing pads.
On December 22, 1942, Hitler ordered the construction of giant bunkers
for the launching of V-2's, the first one to be started in Pas de Calais
as a matter of urgency. A special mission inspected the St. Omer area and
chose Eperlecques as the site for the first Bunker. In March of 1943, Organization
Todt engineers descended upon the Eperlecques Forest about five kilometers
from the town of Watten (Calais, Saint Omer), France, to begin construction
of the first enormous rocketlaunching bunker. Plans for the bunker had
been drawn up in January and February by experts from both Peenemünde
and Organization Todt. This enormous concrete bunker was to accommodate
V-2 reception and storage, preparation of rockets for launch in a sheltered
and controlled manner, on-site production of liquid oxygen, and launch
control with two firing pads. The project was code-named Kraftwerk Nord
West (KNW).
After first looking at a few places around Zouafques near Nordausques in
particular, they decided on the area around Eperlecques. This location
was chosen for several reasons. For the bunker to be logistically accessible
during construction, -and then afterwards accessible for operational supply,
it had to be built close to the Calais canal and a railway linking Calais
to Basle. There was a double railway line linking Saint-Omer to Calais
and a navigable canal for large barges. The site would be sheltered somewhat,
with the location being at the foot of a forest that rose some 90 meters,
sloping away from England and just inland enough to be out of range of
naval guns. The roads were excellent near Watten and electrical supply
was available because high-voltage power lines were in place already in
the area.
120,000 cubic metres of concrete would be required, and the bunker would
have to be built in only four months. Inside the bunker the Germans intended
to build a factory to produce liquid oxygen, to avoid losing oxygen through
evaporation if it were transported. An extensive ventilation system was
planned, including anti-toxic gas filters where the fuels and explosive
warheads were to be stored. There would also be lodging quarters for 250
soldiers and a mulitude of anti-aircraft batteries around the bunker.
A large transformer in Holques, near Watten Eperlecques, was able to provide
enough current for the compressors to manufacture liquid oxygen. The Germans
would use four Heyland compressors to manufacture liquid oxygen, each one
using the Claudets' system of gas conversion to liquid. They intended to
install five of these compressors in the building. Each one could produce
540 kg per hour. This would allow the launching of about ten rockets a
day. However the bunker was built to launch a maximum of 36 rockets a day
so the production of liquid oxygen on the site itself would not be enough.
More liquid oxygen would have to be transported to the site to meet the
36 per day target.
V-2's were planned to be assembled in the northern portion of the bunker.
This part of the site was accessed by two normal railway tracks linked
to the track Calais-Saint Omer. This was for supply of rockets and materials.
Between these two tracks, big trucks were to drive and park for access
to the bunker (this side of the building has been greatly damaged by the
bombardments but is still visible today). To the south was the hall were
the V-2's were to be assembled and checked, and the location of the five
compressors to produce liquid oxygen. On this route taken by the rockets,
the forward gallerys were where the V-2's were to be lifted up vertically,
then fuelled and warheads attached. Lastly, the detonators were fixed in.
The V-2's would then go through the eighteen meter high pivoting door (which
can still be seen today). From there it would revolve 90 degrees and go
towards the outside of the building through either of two corridors. On
the exterior firing pads the rockets would have been launched toward England.
No doors were planned where the rocket would exit the bunker. A perpendicular
door would be installed at the back of the corridor, away frorn the gases,
to minimise the blast of launching rockets. Chicanes can be seen today
on the side walls of this corridor. This was to was break the shock wave
as the rocket was being launched.
In late March, thousands of laborers and earth moving equipment took over
the site. This construction site required an enormous labor force. It consisted
of 35,000, mostly Frenchmen liable for obligatory work service (S.T.O.);
also Belgian, Dutch and Russian prisoners (after the August 27, 1943 bombardments).
The local population believes the structure is to be an electric power
station. The rate of progress was amazing due to advanced mechanization
that included excavators, concrete plants and pumps, etc. Laborers worked
night and day during 12-hour shifts. The materials were transported by
a narrow gauge railway line to the site. The deadline of completion was
set for the end of October 1943.
There was no local railroad to the bunker area originally. This railroad
was ordered built on March 29, 1943. The length was 12 km and it was connected
to the railroad Watten-Duinkerke-Rijsel. Sophisticated concrete pumps allowed
the concrete to be sent directly from the mixers towards the various points
of construction. The vast site was linked to the places where the materials
were unloaded by a two way railway track. Near the town of Watten workers
unloaded the gravel, sand and cement from the barges onto small trains
which were going up and down the forest of Eperlecques 24-hours a day.
The railway travelled over a wooden bridge, through the forest, to the
place where the concrete mixers were working. The concrete mixers got their
supplies through the force of gravity, which helped speed the process.
On April 13, 1943, the Obertsleutnant Thom, accompanied by Schmid from
Organisation Todt, came to visit the construction and took a series of
panoramic photos of the works. On these photos you can see the site with
the concrete mixers, the Decauville tracks with little steam engines,
which were used to transport the materials for the construction.
It would require 4.7 tons of liquid oxygen to launch one rocket. The German
specialists estimated a loss rate of one percent per hour due to evaporation
in storage and allowed for an additional five tons per rocket. This indicated
a projected delay of more than four days between liquid oxygen manufacture
and rocket launching, which brought the required amount to around 14.4
tons per rocket. Hitler fancifully decreed that the bunker should start
by firing 144 rockets each day. This schedule would therefore have required
about 2,073 tons of liquid oxygen per day. However, at the beginning of
1943, the total German production, including liquid oxygen plants in the
occupied territories, would only allow for approximately 200 tons per day.
On March 3, 1943, a letter was written in which the Germans were planning
23 production compressors, of which five would be at Watten. All 23 compressors
together would have had a capacity of 84,000 tons per year, which added
to Peenemünde, would have given 102,000 tons per year, or a rate of
fire of about 19 missiles per day.
The October, 1942 plan was for a bunker LOX plant (3 were planned: Watten,
Wizernes, Sottevast) to have 6 compressors, each producing 540 kg/hr, or
about 13 tons every day, a total for all 6 compressors of 78 tons every
day. At the rate of 15 tons per missile, this would have been enough for
about five V-2s per bunker, per day. However, if the missles were launched
from close proximity to the bunkers, the 5 tons per missle allowance for
evaporation could have been significantly reduced. This would translate
into an almost 50% increase in the number of V-2s that could be launched
for a given supply of LOX. On March 3, 1943, a letter was written in which
the Germans were planning 23 production compressor units, of which five
would be at Watten. All 23 compressors together would have had a capacity
of 84,000 tons/yr., which added to Peenemünde production of LOX, would
have given 102,000 tons/yr., or a rate of fire of about nineteen V-2s per
day.
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When construction
on the Blockhaus started, the locals were more than
certain that it was an electric power station that was being built. As
for the authorities in London, as the war archives show, the British did
not know for a long time for what real purpose of the construction was.
Even the Resistance does not seem to have known the real aim of this construction.
It was deemed to be a high priority target however, since the Germans were
obviously building it for a "special purpose".
The Defense Committee of the British War Cabinet decided the Allies must
attack German rocket installations quickly. Following the August 17, 1943,
bombing mission against Peenemünde, the RAF turned its attention to
the French coastline. The Germans had proposed firing rockets against cities
in southwestern England as well as the large population center of London.
For the battering of London, the Germans needed catapult installations
for the V-1s and either bunkers for fixed V-2 operations or supply depots
for mobile operations in the Pas de Calais area. For the other targets
such as Aldershot, Winchester, Plymouth, and Southampton, the facilities
would need to be located in Normandy. It is unknown exactly how many launch
sites were planned, but it may have been as many as 40 to 50 V-2 sites
and 60 to 100 V-1 sites, all in a wide semicircle from Dunkirk to Cherbourg.
The joint effort by the Allies to counter the German rocket threat was
known as Operation Crossbow. Given the perceived potential danger
posed by the V-weapons, the whole of RAF Bomber Command and an appreciable
number of heavy bomber units from America’s Eighth Air Force were now tasked
with destroying the German rocket sites. Almost half of all Allied photoreconnaissance
was now devoted to the rocket threat.
On May 16, 1943, the first aerial photographs of the Blockhaus at Eperlecques
had been taken by RAF reconnaissance aircraft. As the RAF planned its night
raid on Peenemünde, photographic over flights at Eperlecques showed
that a number of rail lines and huge underground bunkers were being constructed
near Watten. Intelligence sources reported that as many as 6,000 construction
workers were seen working at the site. The British War Office considered
the building to be "of a special nature" and had already decided to bomb
the site. Subsequent Allied photographs at the end of August revealed construction
workers were in the process of pouring thousands of cubic meters of concrete
on the site.
On August 27, ten days after the raid on Peenemünde, 187 Flying Fortresses
of the Eighth Army Air Force, escorted by 147 P-47 Thunderbolts, attacked
the bunker in the late evening. After crossing the coast, the B-17s were
attacked by German fighters, which took advantage of the lack of coordination
between the bombers. Despite the deadly accurate antiaircraft fire and
attacks from German fighters, the attack continued for about an hour with
a total of 366 bombs being dropped. The 2,000-pound bombs devastated the
huge site, especially the northern section where large quantities of concrete
had just been poured, leaving a hardened, twisted mass. At the time of
the attack, workers had completed more than a third of the total construction.
Some of the forced laborers died in the attack, while others took the opportunity
to escape. During the raid, the Americans suffered the loss of four B-17s,
with 98 others being damaged, along with one P-47 shot down. Upon landing
in England, the crew of one B-17 counted more than 200 flak holes in their
aircraft. The American aircrews claimed a dozen German fighters shot down.
The daylight attack of August 27, 1943, was the first time the German V-weapon
sites had been targeted by the U.S. Eighth Air Force. For good measure,
from August 30 to September 7, the complex was attacked four more times
in smaller raids using medium and heavy bombers.
Officials from Organization Todt soon deemed the northern section irremediably
lost. At the time, German officials still believed the Pas de Calais area
in northern France would be the eventual launching area for V-2 rockets,
and even if the bunker was not used to prepare and fire rockets, liquid
oxygen would still be needed to supply any potential mobile field operations.
During the months of September and October, Organization Todt investigated
the Blockhaus and decided to
complete
the southern portion of the bunker for liquid oxygen manufacturing.
One of Todt’s top engineers, Werner Flos, had an idea to continue the construction
using a technique that would protect the site from aerial bombardment during
construction. He suggested building the roof first and raising it up from
the ground. In November, the southern portion was cleared and new work
started by pouring a concrete roof five meters thick, in sections. The
roof would be raised gradually by using a series of giant hydraulic jacks
and blocks. The exterior and interior walls would be built underneath.
This roof would protect the construction taking place below it. The strata
of each concrete layer were cast, and each time, the roof was raised to
build the outside wall. In this manner the building was raised to 28 meters.
Even though the new building was to be a liquid oxygen production facility
only, features for the movement and launching of rockets were still incorporated
in its new construction. This meant that the Germans might have held out
the possiblity of launching a limited amount of rockets from the site.
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By January of 1944 the construction was completed on the liquid oxygen
factory. The Germans continued finishing the inside and put in three compressors
to make liquid oxygen. The Allies had lost a technological battle to the
5-meter thick roof. The 2,000-pound bombs were having no effect on the
building, if not destoying the rail and road networks. The British had
designed much heavier bombs such as the “Tallboy,” or earthquake-bombs,
each weighing 12,000 pounds. The RAF launched two attacks on the bunker
at Eperlecques using the monstrous bombs. On June 19, 1944, 17 RAF Lancasters
each dropped a single Tallboy bomb on the site, and during the second attack
on July 25, 1944, 15 more Tallboys were dropped. |
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Of the 32 bombs, only one actually hit the bunker. Falling on the northern
lip of the roof, the gigantic bomb was only able to slightly pierce the
shell of the roof. The impact caused hardly any damage to the structure
but shook the building violently. The impact can still be seen, the crater
made in the concrete roof was soon repared by the Germans, which the framing
could still be seen when the site was liberated by the Canadians. Another
Tallboy bomb hit the ground 27 meters from the south side, churning up
the earth and creating a voluminous crater (this amazing crater can still
be seen today in front of the Blockhaus, now a large pond).
The huge bombs, though never piercing the bunker, would cause violent mini-earthquakes
each time they exploded. This prompted the German engineers to remove the
liquid oxygen compressors for fear that they might explode under such conditions.
On July 18, 1944, Hitler ordered the abandonment of the bunker. In the
end, the Crossbow bombing campaign, along with the swift advance of Allied
armies across northern France finally won the struggle against the Blockhaus
at Eperlecques. |
Video:
Blockhaus Aerial View 1945
WMV 2.2 MB |
The Eperlecques site was captured by Canadian troops on September 6, 1944,
just a few days before the beginning of the mobile V-2 operations. In January
of 1945, the Blockhaus again came under attack by American aircrews testing
new bombs.
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