The No 3 Mark 1 Accurate Position Finder (APF) was the fire control component of the Canadian Gun Laying III(c) radar system.
It received the approximate range and bearing of incoming targets from the ZPI (Zone Position Indicator) No 4 MK1. The APF then provided accurate measurements of each target aircraft’s range, bearing and angle to direct the fire of a troop of four 3.7 inch heavy anti-aircraft guns.
The GL III(c) radar system was British-designed and adapted by the National Research Council of Canada. The No. 3 MK1 was the first mobile radar employing centimetric wavelength transmission (microwaves) and went into production in 1941. Canada produced 667 units, with about 250 seeing service in the U.K., while the others were sent to the continent or remained in Canada. The British, Canadian and Australian Armies used the system into the 1950s.
Range: 18,000 yards (16,400 metres)
Detachment: GL III system) 2 radar trailers, power generator, 2 towing vehicles and 30 Gunners