The Sounds of Aeroplanes: Notes on the Experiments Carried Out in 1918 at Butley Experimental Air Station on the Sounds of Aeroplanes

BY the end of 1917 it had become clear that the ultimate possibility of defence against night air raids might depend upon the possibility of hearing the attacking aircraft from the ground; if these could be heard whilst approaching there was reason to suppose that they could almost certainly be brought down by defending aircraft directed by searchlight beams controlled by directional listening apparatus, whilst if they could not be heard from the ground there appeared to be no adequate means of defence against them. It thus seemed probable that, if the war continued long enough, the whole question of attack and defence of important areas by air at night would turn on whether or no some means could be found for effectually silencing an aeroplane at its cruising speed; it therefore became of the first importance to determine as quickly as possible, on the one hand, whether some method could be found by which our own aeroplanes could be silenced, and, on the other hand, whether there was any reasonable chance of the enemy silencing their raiding aircraft sufficiently to frustrate the extensive schemes of defence that we were then preparing.