GL III (c) Radar No 4 MK1 ZPI CDN

The No. 4 MK 1 Zone Position Indicator (ZPI) was a radar used to give an early warning of enemy aircraft to the Canadian GL III radar system. It provided approximate range and bearing of incoming targets to the APF (Accurate Position Finder) No. 3 MK 1, exhibited to the left.

The ZPI would track all aircraft within range and then pass the data of the most threatening aircraft to the APF radar. The radar would then follow the target accurately enough to allow the anti-aircraft guns to engage. The ZPI would continue tracking other incoming aircraft while passing data to the APF.

Radar Range: 45.72 miles (73.54 kilometres)

Detachment: 2 radar trailers, a power generator, 2 towing vehicles and 30 Gunners