Ministry is briefly described. All of the systems were given the official designation Air Ministry Experimental Station (AMES) plus a Type number; most of these are listed in this link. Chain Home Shortly before the outbreak of World War II, several RDF (radar) stations in a system known as Chain Home (or CH) were constructed along the South and East coasts of Britain, based on the successful model at Bawdsey. CH was a relatively simple system. The transmitting side comprised two 300-ft (90-m)-tall steel towers strung with a series of antennas between them. A second set of 240-ft (73-m)-tall wooden towers was used for reception, with a series of crossed antennas at various heights up to 215 ft (65 m). Most stations had more than one set of each antenna, tuned to operate at different frequencies. Typical CH operating parameters were: Frequency: 20 to 30 megahertz (MHz) (15 to 10 metres) Peak power: 350 kilowatt (kW) (later 750 kW) Pulse repetition frequency: 25 and 12.5 pps Pulse length: 20 microseconds (μs) CH output was read with an oscilloscope. When a pulse was sent from the broadcast towers, a visible line travelled horizontally across the screen very rapidly. The output from the receiver was amplified and fed into the vertical axis of the scope, so a return from an aircraft would deflect the beam upward. This formed a spike on the display, and the distance from the left side – measured with a small scale on the bottom of the screen – would give target range. By rotating the receiver goniometer connected to the antennas, the operator could estimate the direction to the target (this was the reason for the cross shaped antennas), while the height of the vertical displacement indicated formation size. By comparing the strengths returned from the various antennas up the tower, altitude could be gauged with some accuracy. CH proved highly effective during the Battle of Britain, and was critical in enabling the RAF to defeat the much larger Luftwaffe forces. Whereas the Luftwaffe relied on, often out of date, reconnaissance data and fighter sweeps, the RAF knew with a high degree of accuracy Luftwaffe formation strengths and intended targets. The sector stations were able to send the required number of interceptors, often only in small numbers. CH acted as a force multiplier, allowing the husbanding of resources, both human and material, and only needing to scramble