Pauke, Pauke!

Freya is a long-range ground radar and beacon.It worked with a frequency of about 125 MHz with a range precision of about 125 m with an angle precision 0.5 degrees.

In 1935 GEMA begins to develop a ground radar with a wave length l=2.40m with separate antennas for transmitting and receiving. By the end of 1936 a prototype radar that locates airplanes at a distance of 80km is shown to Luftwaffe Ob.st Martini (later General of communications). Martini places an order for 12 “Freya” devices and by Fall of 1937 three of them and one “Seetakt” are first employed in military... ... maneuvers at Swinemünde.

By that time GEMA proposes an expansion for Freya that makes it possible to identify friendly planes (IFF). Martini puts in an order for further 3.000 devices.

In September 1939 seven Freya radars are operational for air surveillance. They are movable ground systems with a array mattress antenna that can measure direction and distance to the targets with an azimuth resolution of a good 30°.

In October 1939 the first experimental static Freya radar station is placed on Wangerooge. On 18 December 1939 Freya units locate an enemy formation at a distance of 113 km and demonstrate its early warning capabilities directing Luftwaffe fighters towards it: 15 RAF planes are downed.

On April 1940 among some captured radar devices delivered to the DVL there are some British devices that that are mechanically modulated at a 12m wave length. At first their purpose is unclear because switching at the decisive wave length is regularly dispersed with the help of an accelerator switch. At the DVL, a tiny piece of wire gives rise to the conjecture that it is part of a connection between the end and feedback stages. Then the received and amplified impulses from the CH increase the feedback stage so that it sends back an identification impulse on the CH wave. Because the Air Force Ministry of the Reich (RLM) does not accept this explanation, the German Aeronautic Research Institute (DVL) switches an R3000 device to the “Freya” frequency. The subsequent test removes all doubts and furthermore shows that the device increases the range of the “Freya” to a good 150km. Later units are captured that cover all other wave length ranges of the English coast radar. (1)

When on 27 February 1942 a British assault commando captures the steering part and the antenna head of a Würzburg installation the German radar devices are changed to variable frequencies as a prevenvite measure, so Freya changes to l=2.30-2.50m.

Kammhuberlinie
By the end of 1941 General Kammhuber starts to build the "Himmelbett" system of defense. It consists of a network of fighter aircraft control centers. In this scenario “Freya” devices have an important role providing the backbone of early warning and air surveillance for Himmelbett.

Freya parasite and IFF
To be able to use the Freya device to guide fighter planes and to identify friendly fighter aircraft from enemy, Lieutenant Diehl adds a short wave transmitter to his radar. On 5 May 1940 Lt. Diehl succeeds in guiding German fighter aircraft to English bombers 50 km away above the North Sea so that two bombers are shot down.

Illuminated Night Chase with “Freya” Parasite
Spotlights are first guided by a “Freya” radar to spot enemy airplanes even in overcast skies or bad weather. This is combined so that the night fighter aircraft can locate more easily enemy airplanes. On 16 October 1940 the first successful downing of an enemy airplane by this tactic is achieved.

Freya jamming
On 17 August 1942 is first deployed at an attack of American airplanes on Rouen.

In 1942 the jamming transmitter “Moonshine”, developed by the British operates on the wave length of the Freya. The pulse received by the receiving section and rectified is multiplied by a Multivibratorschaltung – similar to the German procedure “Garmisch-Partenkirchen” – and then sent out again by the transmitting section so that it simulates a group of airplanes. To keep up the deception, the Freya frequency has to be monitored constantly to quickly adjust to each change in frequency.

In 1943 the Americans build the onboard jamming transmitter “Carpet I” that jams the entire frequency range of the “Freya” radar by noise modulation.

During the night of 24/25 July 1943 Window is first used at a massive attack of 800 bombers on Hamburg. Since the “Würzburg” devices are almost completely blinded by 92 million windows, the Flak is powerless. Even the night fighter planes cannot attack because neither the “Würzburg” radar nor the “Freya” radar disabled by jamming transmitters on board the bombers can guide them to the bomber convoys. The “Lichtenstein” radar does not help them either since it is also compromised by the Window smoke screen. This is why the English lose only three airplanes at the devastating attack at Hamburg. At the three further attacks in July 1943 the losses remain below 3 percent.

Mandrel. After a big part of the German radars had been destroyed by bombs, three groups of airplanes equipped with 2.40m jamming transmitters are deployed over the English Channel in order to destroy the remaining “Freya” installations.

Sub-types
There were many types of installations among them the most frequent were the standard Freya (FMG39G-fb) and the Freya LZ (FMG40G-fb), of which LZ stands for Lufttransportabel und zerlegbar.

In all 2.000 Freya units are delivered during the whole war.

Technical data
Intended purpose: flight-announce (early warning) and hunt-experience-turn out
Search area: 360°
Range:
Fleightheight range
50m 20km
100m 30km
1000m 60km
3000m 100km
8000m 120km

Distance measuring accuracy: ±150 m
Bearing accuracy: Page ± 0,5o

Large one: Height: 9 m; Width 6 m
Further development
The evolution of Freya are Wassermann (="Aquarius”) a Ground Radar of l=2.40m and Mammut. It consists of a Freya array Freya equipped with tall, highly focusing antennaes. The installation attains a range of 300km.

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1 Gerhard Hepcke, "The Radar War"