Eperleques is a small village in northern France, north of St Omer.
The blockhouse in the nearby woods is a vast concrete structure built by the Nazis during the Second World War for the V-2 rocket.
It is the largest bunker in northern France and was originally intended as a factory and launch facility for the V2. This function was transferred to the nearby site of La Coupole before Eperleques was completed and the bunker was instead used in producing the liquid oxygen necessary for the rockets' fuel.
120,000 cubic metres of concrete were employed in the construction which was undertaken during summer 1943 using largely slave labour working for the Todt Organisation. A complex system of railway lines brought the workers and concrete on site from Calais and St Omer. Eperleques was designed to be able to launch 36 rockets per day and also make sufficient liquid oxygen to fuel them, a daily requirement of 65 tons of it. By combining the fuelling and launching at the same heavily fortified site, the Nazis were able to avoid the risks of transporting the volatile liquid oxygen. The site was given the codename Kraftwerk Nord West (KNW).
Four 4-storey high Heyland compressors were intended to be installed to make the liquid oxygen and the rockets were to be assembled in the northern part of the site and moved on trollies to be launched in the southern part.
On 27th August 1943, the USAAF bombed the site and were able to damage the north of the structure sufficiently to make the Nazis rethink their construction plans. They decided to cast a 5m thick concrete shell and lift it up with hydraulic jacks . The final structure built using this method was 28m high with matching vertical walls which were added incrementally as the roof was raised. This technique permitted construction to continue in spite of repeated allied bombings using munitions of up to 1 ton.
Even so, the Nazi command conmsidered the site too vulnerable and instructed the engineers at Eperleques to concentrate on liquid oxygen production for their new underground launch site at La Coupole, using three Heyland compressors. Eperleques' name was changed to KNW ALT (KNW Old) to reflect this. It seems to have maintained the capability for launch however and some historians believe the engineers at Eperleques still worked on this part of the site as a standby option, with or without official permission.
By 1944, the allies had developed larger bombs and in June of that year a 6 ton RAF Tallboy bomb hit the northern part of the site. The damage was repaired but the D-Day landings and subsequent liberation of northern France ended production at Eperleques and La Coupole before either could launch a rocket. The Nazis switched to mobile launch vehicles in order to fire the V2s.
Eperleques is protected under French law as a historic building and is open to the public.