Oboe (navigation)
Oboe ( O bserver B ombing O ver E nemy) was a British radio navigation system for bombers during World War II . The system was put into operation from December 1942.
Technical details
Two transmitter systems , which were sufficiently far apart from each other in England , sent signals to a mosquito bomber equipped with a corresponding transponder , which acted as a scout . The transponder sent the signals back to the stations. The distance to the transmitter systems could be calculated from the time it took for the signals to do so.
Each broadcasting station defined a specific broadcasting circle, which was chosen so that the intersection of the broadcasting circles of both stations was aligned with the intended target. The Mosquito flew along the circumference formed by one of the stations, the so-called "cat", and threw its load, which consisted of bombs or flares depending on the mission, exactly at the intersection with the second signal, the so-called " Mouse “(mouse). A whole network of oboe stations was set up in the south of England, and each of them could be used as a “cat” or “mouse” as required.
The first “Mark I” oboe emerged from the chain home system, which worked with a wavelength of 1.5 m in the 200 MHz range. The stations sent a series of pulses at a frequency of 133 pulses per minute. The pulse length could be set to be long or short, so that a series of dots or lines was formed as with Morse code . If the aircraft was too far within the defined radius, the "Cat" only sent point signals, if it was too far outside, only line signals were sent.
If the "Mouse" station sent five lines and one point, this was the signal for the bombing. The mouse station contained a bomb calculator called "Micestro", which could calculate the exact time of the launch. This also made it unnecessary to carry a bomb sight in the mosquito bombers themselves.
The basic idea for oboe came from Alec Reeves of Standard Telephones and Cables Ltd. and was developed jointly with Frank Jones by TRE .
Usage history
The oboe was introduced around the same time as the H2S in December 1942. Because of the observed curved trajectory of the bombers, the system was called boomerang in Germany . The predictable trajectory was a weak point of the system, but it was compensated for by the high speed and altitude of the mosquitos. The German Air Force had great difficulty intercepting the mosquitos.
A disadvantage of the system was the limitation of the range due to the curvature of the earth, since the signal transmission only worked directly between the transmitter and receiver. With this, targets in the Ruhr area could be targeted, but more distant targets in Germany could not be reached.
The accuracy of the oboe system was very precise at 110 meters at a distance of 400 km, comparable to optical target devices. In the final phase of the war, aid deliveries were also dropped via the Netherlands, which was still occupied by Germany . The supply points were previously prepared by the Dutch resistance movement and the food containers landed within a 30 meter radius of the target point.
It took Germany more than a year to discover the secret of this system. It was discovered at the end of August 1943 by engineer H. Widdra (who had already discovered the British "Pips Squeak" method in 1940) with the radio measuring station "Maibaum" in Kettwig near Essen , while British bombers were flying an attack against the steelworks " Bochumer Verein " . Then an attempt was made to neutralize the oboe signals with interference signals in the corresponding 1.5 m or 200 MHz range. The British then switched their system to oboe "Mark III" with a wavelength of 10 cm and a frequency of 3 GHz, while at the same time they continued to transmit on the old frequency and wavelength, just to mislead the Germans.
Oboe-like systems
Remarkably, Germany used to a limited extent a conceptually comparable system on the Eastern Front , in which two Freya radar systems took over the role of "cat and mouse" and the bombers were guided by voice transmission. Although a lot of effort was put into the development of navigation systems in Germany, this concept was not used any further.
In addition to its limited range, the oboe had another limitation: it could not be used by more than one aircraft at the same time. The British therefore reconsidered the oboe and developed a new system called the GEE-H (also known as GH). It was based on the same principle as the oboe, but with the difference that the output signal was now sent from the aircraft and the ground stations worked as transponders. Several aircraft could use the two stations in parallel, as randomly generated signals were inserted between the pulses sent by the aircraft. The receiver on the aircraft was able to filter out the transmission pattern that is characteristic of the aircraft from the returned signal. Each receive-response cycle took 100 microseconds in the transponder, which meant that a maximum of 10,000 connections per second was possible and "collisions" were unlikely. In practice the limit was about 80 aircraft at the same time. The designation "GEE-H" is misleading, as the principle was very similar to that of oboe and less of GEE . Apparently this name was chosen because the system, like GEE, worked in the range from 15 to 3.5 m and 20 to 85 MHz. It was about as accurate as oboe.
swell
- Alfred Price: Instruments of Darkness: The History of Electronic Warfare. Peninsula, Los Altos 1977, pp. 123-124, 189-191, 208.
- RV Jones: The Wizard War: British Scientific Intelligence 1939-1945. Coward, McCann and Geoghegan, New York 1978, pp. 274-277.
- Brian Johnson: The Secret War. BBC, London, Methuen, New York 1978, pp. 89-91.