Located between the villages of Halinghen and Verlincthun south east of Boulogne-sur-Mer, there is just one building which remains at Stp Freya, a construction for Germany’s early-warning Freya radar system.
One of the most frequent type of radar used during the Second World War with over 1,000 employed in the defence of occupied lands, Freya was a aircraft detection radar with medium to long-range capabilities with some versions capable of intercepting Allied planes at 200km distance.
Freya was a small but powerful antenna system which was easy to rotate towards targets and its position on the high ground here would have given it an area of coverage including the port city of Boulogne and the west Pas de Calais coastline, where there were also additional radar positions.
The radar here – likely to be a FuMG450 type – had a range of 120km and stood on a concrete base inside an octagonal building with a brick outer and block interior surrounding wall of 2.6m high.
The building measures over 9m wide and has a single entrance with small rear area for a generator, technical equipment and personnel access. Close inspection of the concrete base shows a trough to support the radar’s base unit and a series of rusted bolts where it would have been secured to the concrete.
The blocks and bricks have fared relatively well over the past 80 years of exposure to the elements – even if the mortar between the layers hasn’t. Most recently, it appears to have been used to store farm equipment and fencing, some of which can be found inside today.
Around 750 metres further inland you can see the remains of another radar system – this one for directing bombers to their targets rather than detecting Allied aircraft.
In order to improve the accuracy of night-time or low visibility bombing raids, German forces developed a system known as Knickebein – their first-ever radio guidance system – which broadcast medium frequency radio beams from large antennas based at strategic locations.
Knickebein translates to ‘bent leg’ or ‘crooked leg’ and refers to the dog-leg shape of the FuSan 721 antenna used to broadcast the radio beams.
The beams were based on morse code and were a series of dots and dashes which could be detected by a lead aircraft in a bombing raid. If the aircraft detected dots or dashes, they knew they were off target to the left or right and it was only when the radio operator/navigator onboard heard a single tone that they knew they were in direct line of flight to their objective.
A third beam would also be broadcast to enable the aircraft to determine the range to their target and it’s believed the system enabled the bombers to deliver their payloads within a 1.5km radius of accuracy – far better than previous unguided raids.
By June 1940, British intelligence services had detected the broadcasts and were able to jam the signals destroying the accuracy of raids, leading the Germans to develop more precise and robust systems including the X-Gerat and later Y-Gerat guidance systems.
The Luftwaffe-run facility at Mont Violette – known as site K6 - featured a FuSan 721 type antenna mounted on a 10m diameter circular track plus a crew bunker with a ‘computing room’ and a large generator. This site also featured two open emplacements for 2cm anti-aircraft guns.
You can still make out the track outline where the antenna was once located but it is completely overgrown and now supports a mobile phone mast instead. Only the remains of the other buildings can be seen with the chimneys of the command and generator bunker visible in the farm field on the other side of the road and an overgrown mound where the anti-aircraft gun was positioned.
This site was one of six early radio guidance sites built in France to support bombing raids on England. The other five Knickebein sites in France can be found near Sortosville-en-Beaumont, Cherbourg, Caen, Dieppe, and Brittany with other stations in The Netherlands, Germany, Italy, and Norway.