The essence of flash-spotting to locate HBs was to get accurate cross-observation of muzzle flashes from at least three different positions, the flashes being either directly observed muzzle flashes or 'sky flashes'. The real trick was to ensure that the widely separated observers were all looking at the same flash. Flash-spotting troops were organised into an observation section of flash-spotting posts (FSP) that reported their observed bearings of muzzle flashes to their troop HQ. This HQ provided the plotting centre. which controlled the FSPs and determined HB locations by plotting the bearings they reported, and had an intelligence task of collating their reports. Flash-spotting became harder with increasing German use of flashless propellants from mid-war (although there was more smoke), longer range guns deploying further back also made it difficult as did the practice of deploying guns behind a ridge to mask their muzzle flash. However, in the final months of the war German use of flashless propellants grew less and flash-spotting success increased correspondingly.
TPBM.....10 May 1972