Benito.

This is coolbert:

In several previous blog entries I have mentioned Benito. The German beacon system used during World War Two [WW2]. And I also mentioned that what I had said originally was incorrect. Benito was not a series of Beacons on the ground on English territory operated by German secret agents. Far from it!

Let me clarify.

The Germans at the start of the war made widespread use of "beam systems" to guide their bombers to targets in darkness:

"The Battle of the Beams

The Lorenz blind landing system had been in use for some time in commercial aviation. It consisted of a double beam transmitted from the end of the runway. In foul weather a pilot could ride the beam down to a landing. If he was "on the beam" he would hear a steady tone; if off to either side, dots or dashes. The Germans used a Lorenz system in reverse; instead of guiding a plane to a runway, it was led away from the runway and towards the target. The usual blind landing system had a range of 30 miles, but the Germans had fitted their bombers with ultra-sensitive receivers.

Professor F. A. Lindemann, scientific advisor to Winston Churchill, maintained that such a beam could not follow the curvature of the Earth. Dr. R. V. Jones of Air Scientific Intelligence believed the evidence showed otherwise." [an American amateur radio operator prior to the war had done extensive research into the propagation of VHF radio signals and had determined they could propagate in ways not believed to be possible].

The British came across a system, more sophisticated than what they had encountered before. This was Wotan:

"Wotan

Ultra messages revealed yet a third menace, Y-Geräte, or "Wotan". Dr. Jones asked Professor Norman of BP what was the significance of Wotan. Norman replied, "He was head of the German Gods, and had one eye. One eye! [Wotan in myth was said to have plucked out one eye and offered it to another god who gave in return to Wotan wisdom. Norman must have been a British university Don working for BP [Bletchley Park, the place where Ultra was decrypted]]. A single beam!" And it was a single-beam system in which the ground station transmitted two signals; one for direction and a second for ranging. The airplane picked up the beam signal and re-transmitted it back to the sender. The distance of the aircraft from the ground station was calculated from the time it took the signal to return, and the bombs were dropped automatically at the correct point. Paradoxically, this system was easier to jam than the first two. The British simply picked up the re-transmitted signal from the plane, and returned it to the ground station. This resulted in confusion to the enemy who could not know if it was coming from the plane or the ground."

Further, the Germans also christened this system Benito. Benito [named in honor of Mussolini] was a German Lorenz type system, but consisting of one beam of radio energy. Named Wotan II or Y-Gerat:

"the Germans began deploying Y-Gerät or Wotan II. This system was unique in that it used only one Lorenz type beam along which the bombers would fly. A second transmission around 45MHz was aimed at a transponder in the aircraft, which re-transmitted on an offset frequency [this method is called interrogation]. The home station was able to deduce the range of the aircraft, and hence distance from the target, by calculating the return delay. The home station would order the release of bombs or markers as the aircraft reached the target. The system was potentially very accurate."

To deceive the German Y-Gerat system, the British devised "Domino", the counter.

"'Operation Domino'. Using the receiving station at Swains Lane, Highgate, the return signal from the aircraft's transponder was retransmitted back to the aircraft on its receiving frequency by the Alexandra Palace TV transmitter and hence back to the aircraft's home station. This extra loop producing a false distance reading."

And the counter-measure of the British was a success:

"The 'Domino' counter measures from Alexandra Palace were a complete success and by the spring of 1941 the Germans had abandoned all the beam systems against Britain."

Read about the Y-Gerat system by clicking here. [this site has some excellent drawings illustrating exactly the counter-measures involved in Domino. Also has an excellent photo of a Benito transmitting antenna].

Also go to this site by clicking here to see a historical first hand account of a Domino counter-measures operator in action.

Go to this site by clicking here to see illustrations that show the X-Gerat and the Y-Gerat systems.

Now, what does the Y-Gerat system categorize as? Is it just a beacon or is it a form of radar? The operator on the ground does know that the plane he has interrogated is in the beam path, or a return signal would not have been received. So the direction of the interrogated aircraft is known. And from the return signal to the interrogation, the distance with a pretty good degree of accuracy can be also determined [as long as the return signal is not jammed]. So is this a form of radar then? Not a radar as normally thought of. But close. On some web sites it is referred to as a "radar". Not a radar as usually defined. But can be thought of as such to a degree.

coolbert.