682al
It's an Azimuth indicator for a Leigh Light. The arc of movement suggests it would be for a light installed on the starboard wing, e.g. Catalina.
That sounds good to me especially given its range of movement highlighted below in bold would make a perfect match.
Anti-submarine operations - The Leigh Light. | Military History Forum
THE LEIGH LIGHT FOR NIGHT ANTI-SUBMARINE OPERATIONS
The Leigh Light was a carbon arc searchlight carried on an aircraft and used in conjunction with A.S.V. to illuminate surfaced submarines at night. The searchlight operator was situated in the nose of the aircraft from where he could control the searchlight beam in both elevation and azimuth. Indicators were fitted which showed the direction in which the beam would shine. The operator was thus able to train the searchlight in approximately the right direction and distance before the light was exposed. A lens giving a spread of 10° in either a horizontal or vertical plane was provided which made search¬ing for the target easier, but some expert operators prefer to use the light without the lens. The maximum effective range in ordinary -weather was about two miles.
The arc lamp was fully automatic in operation, the rate of feed of the Carbons being automatically controlled. Power for the arc, which ran at 120 to 150 amperes, was obtained from seven 12 volt 40 ampere hour type D accumula¬tors and a-trickle charge fitment -would maintain them fully charged provided the arc was not run for more than three half minute periods per hour. Fully charged accumulators \?would maintain the arc for about six minutes without re¬charging.-
There were two types of Leigh Light in service:-
(1) The Turret type, fitted on Wellington aircraft; in this a 24 inch
searchlight was mounted in a retractable under-turret and the controls were
hydraulic. The maximum beam intensity was 50 million candles without the
. Spreading lens and about 20 million candles with the lens. Total weight of the installation was 1,100 Ibs.
(2) The Nacelle type, fitted on Catalina’s and Liberators; in this a 20
inch searchlight was mounted in a nacelle 32 inches in diameter slung from
the bomb lugs on the wing. The controls were electric and the maximum beam
intensity was 90 million candles, without the spreading lens and about 17
million with the lens. Total weight of the installation was 870 Ibs.
The trickle charging current for the accumulators was obtained from an engine-driven generator on the Wellingtons, windmill driven generator on Catalina’s and a motor generator set on Liberators.
The control system on the Wellington was similar to that used for turrets. The turret itself was rotated by a Vane oil motor for movement in azimuth and the projector was moved by a ram inside the turret for movement in elevation.
The maximum speed of rotation when the control column was turned to the limit was 40 degrees per second, the limits of movement were 60 degrees to Port and 180 degrees to Starboard.
