This was never a fort, but after the German invasion the local
population were excluded from all sensitive sites such as this and it became
known as " The German Fort".
On the same day that this region of France fell to the invading Germans they
were seen surveying this site. (June 18th 1940)
They needed a site on high ground on which to build a new and early form of
radio guidance, permitting planes to fly by night.
Radio navigation systems had been in use for a few years, used by both military
and civilian aircraft.
This usually took the form of a transmitter at the destination or on the route,
and the plane flew along the signal.
This could be used for bombers returning home after a mission, but could not
obviously be used on the outward leg.
It was also very inaccurate for a flight of over 200 kms, so the reverse of this
system was needed.
The Germans were the first to use such a system (Knickebein) and the two
navigation beam transmitters were installed here and at Mont Pincon.
The transmitter here was operational in late 1940 (although not in the bunker),
and was first used for the bombing of Coventry on November 14th 1940. (The
The transmitters sent out two parallel signals, one dots and the other dashes.
When the plane was on course, between the two signals a steady tone was heard.
This later system was called the X-Gerat and was later refined to use four
This system had a very limited life span and the beams were very easy to jam by
the RAF and even when the Germans changed frequencies several times during a
raid, it was able to be blocked.
This station was vital for the night bombing of England.
For an explanation as to how the system worked, have a
look at Beaumont Hague K9 in this section.
Luftwaffe station K10 Knickenbein FuSAn 721 - Water reservoir