Looking better! Suprising it has survived, let alone been published as such documents were 'Most Secret'. Sound ranging was the first artillery detection system capable of giving a bearing that alowed counter battery fire on an unseen target. The other system used was flash spotting. Artillery developed into a science during the Great War, before that it was open sights, point and shoot.
http://nigelef.tripod.com/tgtacqcb.htm