The IFF Mark II antenna on this Spitfire can just be made out, stretching across the rear fuselage from the roundel to the tip of the horizontal stabiliser.
IFF Mark II was the first operational identification friend or foe system. It was developed by the Royal Air Force just before the start of World War II. After a short run of prototype Mark Is, used experimentally in 1939, the Mark II began widespread deployment at the end of the Battle of Britain in late 1940. It remained in use until 1943, when it began to be replaced by the standardised IFF Mark III, which was used by all Allied aircraft until long after the war ended.
The Mark I was a simple system that amplified the signals of the British Chain Home radar systems, causing the aircraft's "blip" to extend on the radar display, identifying the aircraft as friendly. MarkI had the problem that the gain had to be adjusted in flight to keep it working; in the field, it was correct only half the time. Another problem was that it was sensitive to only one frequency and had to be manually tuned to different radar stations. In 1939, Chain Home was the only radar of interest and operated on a limited set of frequencies but new radars were already entering service and the number of frequencies was beginning to multiply.
Mark II addressed both these problems. An automatic gain control eliminated the need to adjust the gain, making the device much more likely to be working properly when interrogated. To work with many types of radar, a complex system of motorised gears and cams constantly shifted the frequency through three wide bands, scanning each every few seconds. These changes automated the operation of the device and made it truly useful for the first time; previously, operators could not be sure if a blip was an enemy aircraft or a friendly one with a maladjusted IFF. Originally ordered in 1939, installation was delayed during the Battle of Britain and the system became widely used from the end of 1940.
Although the Mark II's selection of frequencies covered the early war period, by 1942 so many radars were in use that a series of sub-versions had been introduced to cover particular combinations of radars. The introduction of new radars based on the cavity magnetron required different frequencies to which the system was not easily adapted. This led to the introduction of the Mark III, which operated on a single frequency that could be used with any radar; it also eliminated the need for the complex gear and cam system. Mark III began entering service in 1943 and quickly replaced the Mark II.
new frequencies. Instead of putting Mark I into production, a new IFFMarkII was introduced in early 1940. MarkII had a series of separate tuners inside...
IFFMark X was the NATO standard military identification friend or foe transponder system from the early 1950s until it was slowly replaced by the IFF...
IFFMark III, also known as ARI.5025 in the UK or SCR.595 in the US, was the Allied Forces standard identification friend or foe (IFF) system from 1943...
Leader Sidney Lugg installed an IFFMarkII transponder at the base, tuned to operate on the ASV frequencies. The IFF system broadcast a short pulse of...
to be used in specialized roles into the 1940s, for instance in the IFFMarkII. There was one role where the regenerative system was not suitable, even...
signal, causing interference with other radars. This was addressed in the IFFMarkII with the addition of an automatic gain control system, which amplified...
During World War II, the German Luftwaffe relied on an increasingly diverse array of electronic communications, IFF and RDF equipment as avionics in its...
attacks on the Burma Road. The British Royal Air Force begins to install IFFMarkII, the first operational identification friend or foe system. October 1...
"Firstborn", "Debut", sometimes FuGe) was an identification friend or foe (IFF) transponder installed in Luftwaffe aircraft starting in 1941 in order to...
upgraded IFF+ from older identification friend or foe system. To better accommodate the pilots, cockpit floor is also reshaped. The upgraded Tejas Mark 1A will...
two built by 1945 Egon - German bomb-targeting system using the Erstling IFF system and two Freya radar ground stations for bomb-aiming. Elephant Cigar...
signal emissions, as well as a device named Perfectos that tracked German IFF. As a countermeasure, the German night fighters employed Naxos ZR radar signal...
followed shortly by an additional order for 54 more Mark Is. In the latter half of 1967, 46 MarkII boats, with a modified deck house set further back...
Air-to-Surface Vessel, Mark III, or ASV Mk. III for short, was a surface search radar system used by RAF Coastal Command during World War II. It was a slightly...
thousands of aircraft involved in the invasion would saturate and break down the IFF system, the marking scheme was approved on May 17, 1944, by Air Chief Marshal...
equipped with the IFF Mk. II system, which allowed radar operators to determine whether a blip on their screen was a friendly aircraft. IFF was a responder...
or BABS. This was also the band that the earlier IFF Mk. II worked on, and was similar to the new IFF Mk. III bands. For the Mk. VIII radar, it was decided...
aircraft, which was transmitting IFF squawks in Mode III, a signal that identified it as a civilian aircraft, and not Mode II as used by Iranian military aircraft...
estimated to be 60 percent more powerful in output with improved EW, ECM, and IFF capabilities. It is tied into the main phased-array radar on a time-share...
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