Airborne Cigar facts for kids
Airborne Cigar, or ABC for short, was a special system used during World War II. It was an electronic countermeasure (ECM) system, which means it was designed to mess up enemy radio signals. The British developed it to jam the radio communications of the German Luftwaffe (air force) night fighters. These radios worked on a specific frequency band called very high frequency (VHF).
When ABC was used correctly, it made it almost impossible for German night fighters to talk to their ground controllers. The Germans even had a nickname for ABC: "dudelsack," which means bagpipes in German, because of the strange warbling sound it made.
The ABC system had a special receiver that could listen to many radio signals and three powerful transmitters. Special operators, who spoke German, would listen for the frequencies being used by the German ground controllers. Once they found a frequency, they would turn one of their transmitters to that same frequency and start broadcasting loud noise. This noise would block the German conversations.
The No. 101 Squadron RAF mainly used ABC. This squadron was part of the specialist No. 100 Group RAF. Since ABC was only effective over about 50 miles (80 km), the ABC-equipped planes were spread out among the main group of bombers. Because these ABC planes flew on almost every mission, No. 101 Squadron suffered some of the highest losses of the war.
The Germans tried to stop ABC by using new radio frequencies. But the British quickly found these new frequencies and jammed them too. Other attempts, like using fake ground controllers or having women send signals, didn't work well. No truly effective way to stop ABC was ever found. Later in the war, ABC was replaced by a system called Jostle IV, which jammed the entire radio band at once.
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History of Jamming
Even before ABC, the British were working on ways to jam German radios.
Early Efforts: Tinsel
The idea of jamming German ground-to-air radios started in 1942, when the main British bombing campaign was getting bigger. At that time, the Germans used two main radio frequency bands for their air-to-ground talks: one was the high frequency (HF) band, and the other was the very high frequency (VHF) band.
For the HF frequencies, British scientists developed a system called "Tinsel." This system was put into many British Lancaster bombers. It had an HF receiver that the radio operator could scan to find German signals. When a signal was found, the operator would set their transmitter to the same frequency and send out noise from a microphone placed next to the aircraft's engine.
Tinsel was first used in December 1942. However, it was soon clear that the operators were too busy with their other tasks to keep searching for frequencies. Also, the Germans found a way around Tinsel: instead of talking to single planes, they started using one very powerful transmitter to broadcast a constant update on where the British bomber stream was.
This led to the "Special Tinsel" idea in June 1943. Instead of the aircraft operators searching for frequencies, special listening stations in England (called the Y service) would find them. These frequencies were then sent to the aircraft using coded messages. Two-thirds of the bomber group would then tune their jammers to that signal, creating a strong jamming effect.
In October 1943, another system called Corona was set up. When a German HF frequency was being used, German-speaking people in England would start giving fake orders, like telling German planes to land or saying that certain airbases were foggy. This caused even more confusion for the German night fighters.
Ground-Based Jamming: Cigar
The Special Tinsel system became more and more effective. By spring 1943, the Y service noticed that German night fighters were having more success when they used the newer VHF radio bands. So, on April 7, 1943, the British Bomber Command asked for a solution for these VHF frequencies. This new solution was called "Cigar."
Because the VHF transmitters needed to be very powerful, the first Cigar systems were built on the ground. The first one was set up at Sizewell and started working on the night of July 30/31, 1943. It was hard for the Y service to tell how well this system worked because its jamming made it impossible for them to hear the German night fighter radio traffic.
A bigger problem for Cigar was its limited range. VHF signals don't travel around the Earth as well as lower frequencies. This meant Cigar's effect was limited to about 140 miles (225 km), making it useful only for short-range German raids over France and the North Sea.
Taking it to the Skies: Airborne Cigar
On May 6, 1943, a British Air Commodore named Sidney Osborne Bufton ordered a version of Cigar that could be put into an aircraft. This became known as "Airborne Cigar," or ABC. The ground-based version was then called "Ground Cigar." Bufton also suggested that the planes carrying Airborne Cigar should be called "ABC aircraft" because the name was short and simple.
The system was first planned for No. 100 Squadron RAF bombers. However, these planes were getting new H2S radars and didn't have enough electrical power left for the ABC system. So, No. 101 Squadron RAF was chosen instead, and they used the system for most of the war.
Building ABC for aircraft was difficult. High-power VHF transmitters were quite large back then. To be effective, a plane needed to carry several of them to jam different frequencies. The final ABC system had three transmitters. These broadcasted from two 7-foot (2.1 m) antenna masts above the wing. A special receiver with a shorter antenna was mounted near the tail of the aircraft. The electronic parts of the transmitters were packed into a large cylinder that weighed 275 kg (606 lb). It took 3,000 hours of work to install one system. Because of the extra weight, the plane's bomb load had to be reduced by about 1,000 lb (450 kg).
The ABC system was tested in September 1943 and first used on the night of October 7/8.
ABC required the operator to listen for any broadcasts in the VHF bands. Since these communications were very quick, the operator couldn't just slowly search for them. Instead, a motorized tuner swept the receiver through the entire band 25 times every second. Any signals received would show up as a vertical "blip" on a screen called an oscilloscope. The position of the blip on the screen showed the frequency of the signal.
When a blip appeared, the operator would then tune a second, regular tuner to that same frequency and start listening to the transmissions. They would listen for specific German words, like "kapelle" (chapel), which indicated the target altitude. This helped them identify ground controllers rather than other radio users. To do this, the operator needed to understand German. Many of the Special Duties Operators (SDOs) were Yiddish speakers, including some who had escaped from Germany before the war. Once a frequency was identified as being used by a ground controller, one of the three transmitters would be set to jam that frequency, and the operator would then look for another signal to jam.
Because ABC's effective range was about 50 miles (80 km), and the bomber streams were often much longer, many ABC aircraft had to be spread out through the stream. This meant that many ABC planes had to fly on every mission. As a result, No. 101 Squadron suffered very high losses. For example, between November 1943 and March 1944, the unit lost seventeen aircraft. Seven planes were lost on the night of March 30/31 during the terrible Nuremberg Raid.
Sometimes, the Y service station in West Kingsdown would try to help by identifying frequencies and sending them to the ABC aircraft using code words. However, this often didn't work well due to range limits, so ABC was almost always operated by the SDOs themselves.
One important use of ABC was during the D-Day invasion. To trick the Germans into thinking the invasion was happening near Pas de Calais, a large group of RAF Flying Fortresses dropped window (strips of metal foil) in patterns that looked like a huge paratrooper landing. To protect these planes, all the ABC-equipped Lancasters were used to completely disrupt any German attempts to intercept them.
German Countermeasures
By the time ABC was introduced, the Germans had already experienced several rounds of jamming and knew about the tactic. They introduced new radio rules that allowed ground controllers to quickly tell their fighters to switch to a new frequency if one was being jammed. This led to a "cat-and-mouse" game: ABC operators would hunt down the new frequency and jam it, forcing another switch. Depending on how skilled the ABC operators were, even this frequency hopping could be so disrupted that it made fighter operations very difficult.
Other attempts were made to disrupt ABC. These included having women make broadcasts or playing music on other channels to create fake signals. Another system used captured ABC sets to send out jamming on frequencies they planned to use, tricking other operators into thinking those frequencies were already jammed. The transmitter would then be turned off just before a real broadcast went out.
The Y service soon found that a new frequency band, from 31 to 32 MHz, was also being used by the Germans. This was outside the normal range of the ABC receiver. So, a switch was added to the ABC transmitters that would make them send out noise across this entire new band. This would be activated based on instructions from the Group Operations messages. It's not clear if this produced enough jamming to stop transmissions, but it did show the Germans that the British knew about their new frequencies and were always one step ahead. In any case, the Germans soon stopped using this frequency.
Another way the Germans tried to avoid ABC jamming was by using the now less-useful HF bands to send Morse code instead of voice. Morse code signals are stronger, making them easier to hear over noise. However, this required the radio operator to decode the messages, which was only practical for larger aircraft with more crew. This was quickly countered by a new British system called "Drumstick," first used on the night of January 21/22, 1944. After a Morse code signal was picked up at the Cheadle Y station, Drumstick would send out random dots and dashes, changing the speed to match any potential keying rate from the original German operator.
Later Use of ABC
Even though ABC was effective throughout the war, it needed German-speaking crew members, who were in high demand for other important jobs. Also, these operators were in great danger, and for many who were Jewish, the personal risks if captured were extremely high.
Because of these reasons, ABC was eventually replaced by a new version of the Jostle VHF jammer. Instead of trying to find and jam specific frequencies, Jostle produced 2,000 watts of power and broadcasted it across the entire ground-to-air band. This system didn't need an operator to "hunt" for signals; it simply had to be turned on when needed. Jostle-equipped aircraft would broadcast at random times to prevent German night fighters from using the jamming signals to find them.
The ABC units that were still working were moved from No. 101 Squadron to the Handley Page Halifax planes of No. 462 Squadron RAAF (Royal Australian Air Force). They started operations in March 1945.
ABC continued to be used after the war. The specialist No. 199 Squadron RAF fitted four ABC transmitters to their Avro Lincoln bombers and one to their de Havilland Mosquitos. They later put one on their English Electric Canberra jets, and even later, on their Vickers Valiant bombers, which had enough electrical power for six transmitters. When No. 199 Squadron was disbanded in 1958, the Valiants went to RAF Finningley and became part of the newly reformed No. 18 Squadron RAF. It's not known exactly when the last of these systems was retired.
Beyond these special units, it was the Jostle system that became the model for more modern jammers. It remained in use until it was replaced by a system called Green Palm on the V bomber fleet.
See Also
- Electronic warfare
- Radar jamming and deception
Images for kids
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Avro Lancaster B Mark I, NG128 'SR-B', of No. 101 Squadron RAF bombs over the target during a daylight raid on Duisburg on 15 October 1944. The large aerials on top of the Lancaster's fuselage are the antennas for the Airborne Cigar system.
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RAF Fortress III HB796 at Prestwick, after being fitted with radio counter-measures equipment by Scottish Aviation. It served with No. 214 Squadron RAF of No. 100 Bomber Group, based at RAF Sculthorpe from November 1944. Equipment includes American AN/APS-15 radar in the large radome under the nose, Airborne Cigar radio-jamming equipment, and an Airborne Grocer aircraft radar jamming installation, the aerials of which can be seen on either side of the tail turret. HB796 was lost on 9 February 1945.
