English: Royal Air Force Radar, 1939-1945

Chain Home: CH receiver room at an East Coast station, showing one of the two RF7 Receivers (left) and the Mark 3 Console (right) in use. This is typical of late-war CH stations, which had been semi-automated through the use of an analog computer referred to as the "fruit machine".

On the left, the radar operator's hand is resting on the goniometer control, which allowed her to change the sensitive direction of the receiver in order to determine the bearing of the target. An additional control set an electronic pointer on the display, the "strobe", to lie over a selected target. When both the direction and range were selected, a button was pushed to send this information electrically to the fruit machine.

The fruit machine then applied a number of calculations to these measures to correct for known oddities of the receiver system and geography of the local site, then translated these corrected range and direction measures into map grid references using basic trigonometry. Operators on the right would use this information to develop "tracks" for various targets, updating them on the board hanging from the right wall (only the back can be seen here). Telephones were used to send this information to the various control stations in the reporting chain.