Automatic Gun-Laying Turret

The AGLT Village Inn FN121 tail turret as fitted on a Lancaster — note the radome covering the parabolic scanning aerial.

The Automatic Gun-Laying Turret (AGLT) was a British radar-aimed FN121 turret fitted to some Lancaster and Halifax bombers in 1944. The AGLT system was devised to allow a target to be tracked and fired-on in total darkness, the target's range being accurately computed as well as allowing for lead and bullet drop. The system was referred to by the codename Village Inn during development.

The system, known as TR3548, was devised by a team led by Dr Philip Dee and designed under the aegis of chief designer Dr 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 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 the standard Frazer-Nash turret. It worked on a wavelength of 9.1 cm (3 GHz) with a pulse repetition frequency of 660 hertz. The magnetron used was the CV.186 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 made automatic, the range information being fed electronically directly into the gunsight, with the navigator's "running commentary" only being retained for the benefit of the rest of the crew. The gunner simply maneuvered his guns to place the "blip" in the centre of the gunsight's reticle, and opened fire when the range was appropriate. Windage, bullet drop and other factors were already calculated by the gunsight.

A diagram of the Village Inn scanning system

The first squadron to use Village Inn operationally was No. 101 Squadron RAF, based at Ludford Magna, in the autumn of 1944, followed soon afterwards by No. 49 in the attack on Darmstadt on September 11/12,^[1] 156 and 635 Squadrons.

Liberated prisoners during Operation Exodus with an Avro Lancaster of No. 635 Squadron RAF at Lübeck, Germany, 11 May 1945. The Lancaster at right is fitted with the AGLT "Village Inn" tail turret

Village Inn was eventually produced in four Marks:

AGLT Mark I — initial design — Airborne Radio Installation (ARI) 5559.

AGLT Mark II — modified, improved, Mark I — soon discontinued — ARI 5561.

AGLT Mark III — scanning aerial mounted remotely from turret. Scan independent of turret's movements — ARI 5562.

AGLT Mark IV — ARI 5632

The system was also fitted to the Rose turret on at least one Avro Lincoln B.Mk II, although how many so-fitted is not known at present . Some Lincolns fitted with the Boulton Paul Type D tail turret also incorporated the equipment.^[2]

A similar type of system was produced in the US by the Emerson Company, St Louis, when an Emerson Model III tail turret was equipped with the Emerson APG8 Blind Tracking Radar and fitted to the Canadian-built Lancaster KB805. The system was found to have no advantages over the British system and the project was subsequently dropped.

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Automatic Gun-Laying Turret

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