The Automatic Gun-Laying Turret (AGLT), also known as the Frazer-Nash FN121, was a radar-directed, rear gun turret fitted to some British bombers from 1944. AGLT incorporated both a low-power tail warning radar and fire-control system, which could detect approaching enemy fighters, aim and automatically trigger machine guns – in total darkness or cloud cover if necessary. The radar warning and fire-control system itself was commonly known by the code names Village Inn and "Z Equipment", as well as the serial number TR3548. It was intended that all Royal Air Force bombers, and other Allied aircraft attached to Bomber Command would have an IFF infra-red nose lamp, which would allow rear gunners to avoid friendly fire. In practice, however, Allied aircraft without lamps often crossed paths with AGLT aircraft and, even when they were fitted and operational, the lamps were not always visible to gunners, for various reasons. As a result, Village Inn was generally used purely as an early warning system. According to the official history of the RCAF during World War II, fully automated "blind-firing" was used by gunners in only four out of every 1,000 sorties. Development The system was devised by a team led by Philip Dee and designed under the aegis of chief designer Alan Hodgkin, after receiving a request from the Air Ministry for such a system in early 1943. Village Inn was evaluated and tested by the Telecommunications Research Establishment (TRE) at RAF Defford using the Lancaster Mark I serial number ND712 Lancaster Mark III JB705 and Mk II LL736 and LL737 and subsequently put into production. The system consisted of a transmitter/receiver unit mounted in the navigator's compartment, operating through a conical scanning parabolic aerial attached to rear turrets. It worked on a wavelength of 9.1 cm (3 GHz) with a pulse repetition frequency of 660 Hertz. The magnetron used was the CV186 of approx 35kW. The electronics sent a signal back to the turret, where it was displayed on a cathode ray tube (CRT) display screen positioned adjacent to the gun sight, the image of which was projected on to the Mark IIC gyro gunsight via a semi-transparent mirror. Initially, ranging information was provided only at the transmitter situated in the navigator's compartment and was read off to the gunner over the intercom, the gunner using foot pedals to set the target range on the sight. In production equipment the process was