Airborne Cigar
Airborne Cigar, or ABC for short, was a World War II electronic countermeasure (ECM) system developed by the Telecommunications Research Establishment (TRE) to jam Luftwaffe ground-to-air radios operating in the very high frequency (VHF) band.
The German-speaking Special Duties Operators (SDOs) would listen to signals in the band to determine which frequencies were being used by ground controllers.
The idea of jamming the Luftwaffe ground-to-air radios appears to have been introduced in 1942[a] as the main RAF bombing campaign began to ramp up.
[3] For the HF frequencies, the Telecommunications Research Establishment (TRE) developed the "Tinsel" system that was fitted to many Lancasters.
These were then forwarded to the aircraft in coded terms during the half-hour scheduled Group Operational messages sent from Bomber Command.
[4] In addition, in October, the Corona system was set up; when a frequency in the HF band was seen to be in use, German speakers in England would begin giving out orders to land or indicate that certain airbases were fogged in, causing further confusion.
Unfortunately, it was difficult for the Y service to give any indication of the success of this system because its broadcasts made it impossible for them to hear the night fighter traffic.
A more serious concern for Cigar was a lack of range; the VHF signals did not refract around the Earth as well as lower frequencies, meaning that the effect was limited to the line-of-sight.
In the case of Cigar, calculations suggested it would be effective to about 140 miles (230 km), which made it useful only against short-range raids in France and over the North Sea.
100 Squadron RAF bombers, but as these aircraft were in the process of receiving the new H2S radars, they had no leftover electrical power to run the ABC system.
They would listen for certain keywords like "kapelle", giving the target altitude, to identify ground controllers as opposed to other users.
[1] As was the case for Tinsel, operations were sometimes aided by the Y service's station in West Kingsdown, who would attempt to identify the frequencies and send them to the ABC aircraft using code words.
In order to convince the Germans that the invasion was taking place near Pas de Calais, a large force of RAF Flying Fortresses dropped windows in patterns that looked like a massive paratrooper landing effort.
They introduced new radio procedures that allowed the ground controller to quickly order the fighters to tune to a new frequency in case one was being jammed.
[1] Other attempts were made to disrupt ABC use, including having women make broadcasts [c] or, in other cases, producing false signals by playing music on other channels to waste the SDO's time.
This was outside the frequency range of the ABC receiver, so a switch was added to the transmitters that would cause them to send out noise across this entire band.
It needs to be clarified whether this produced enough jamming to hamper transmissions, and to some degree it was only added to demonstrate to the Germans that they knew of the new frequencies and were one step ahead of them at all times.
[8] Another attempt to avoid ABC jamming was made by using the now-useless HF bands to transmit Morse code instead of voice.
This required the fighter's radio operator to decode the messages, making it useful only for larger multi-place aircraft where someone could be dedicated to this role.
Instead of attempting to identify and jam the specific frequencies being used, Jostle produced 2,000 W of power which it broadcast across the entire ground-to-air band.
199 Squadron RAF fitted four ABC transmitters to their force of Avro Lincolns and a single example in their de Havilland Mosquitos.
[13] Beyond these specialist units, it was Jostle that set the pattern for more modern jammers and remained in use until replaced by Green Palm on the V bomber fleet.
