Serrate radar detector

Serrate was a World War II Allied radar detection and homing device that was used by night fighters to track Luftwaffe night fighters equipped with the earlier UHF-band BC and C-1 versions of the Lichtenstein radar. It allowed RAF night fighters to attack their German counterparts, disrupting their attempts to attack the RAF's bomber force.

The first Serrate systems were developed from the AI Mk. IV radar, which just happened to have antennas almost perfectly suited to receiving the Lichtenstein signals. Serrate simply disconnected the display from the radar's own transmitter and receiver and connected it to one tuned to the Lichtenstein. This produced a display indicating the direction to the German aircraft, but not the range. By carefully watching the movement of the target on the display the operator could estimate the range in general terms, near or far. When it appeared the target was close enough, the display was reconnected to the Mk. IV's own electronics to provide both ranging and directional information during the last moments of the attack.

Serrate operations began by No. 141 Squadron RAF on the night of 7 September 1943. 179 operational sorties yielded 14 claimed fighters shot down, for 3 losses. After that point, the Luftwaffe realized what was happening and quickly introduced new versions of their radars working on different frequencies. Unlike the earlier sets, which just happened to operate on frequencies very close to the British radars, the new sets required entirely new detectors, which took some time to develop. New versions of Serrate were introduced, and moved from the Bristol Beaufighter to the faster de Havilland Mosquito, but later operations were never as successful as the original ones.

Later intruder operations were often directed by the Perfectos device instead of Serrate. This worked by triggering the German IFF transceivers and receiving the reply on the same antennas as Serrate. As the timing of the request pulse was known, Perfectos revealed both the angle and range to the target, removing the need to switch to radar at the end of the approach.