Description
The searchlight was mounted in an armoured turret fitted to a tank. Initially the Matilda tank was used, replacing its normal turret with a cylindrical one containing both a searchlight and a machine gun. This was later replaced by the US M3 Grant which was superior in several ways. It was a larger, roomier and better armoured tank, yet also faster and so better able to keep up with tanks such as the Sherman. It was armed with a hull–mounted gun, which was unaffected by the searchlight turret.
The searchlight turret included a station for an operator. The light emerged from a vertical slit that was just 2 inches (5.1 cm) by 24 inches (61 cm), its comparative smallness reduced the chance of damage to the optical system by the entry of bullets. The beam diverged at 19° horizontally and 1.9° vertically, forming a pool of light around 34 by 340 yards (31 m × 310 m) at a range of 1,000 yards (910 m). The turret could rotate 360° and the light beam elevated or depressed by 10° from the horizontal.
Blue and amber filters allowed the light to be coloured as well as white. A shutter could flash the beam on and off up to twice a second. It was found the blue light caused the CDL tank to appear to be at a greater distance, and blue and amber light beams from two CDL tanks could combine to illuminate a target with white. A flashing beam would further dazzle and disorient enemy troops by not giving their eyes a chance to adapt to either light or darkness.
The project was shrouded in secrecy. It was tested during Exercise Primrose in 1943 at Tighnabruaich, Scotland with the result that it was determined to be "too uncertain to be depended upon as the main feature of an invasion".
Read more about this topic: Canal Defence Light
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