Sound rangers are military specialists who locate enemy artillery using sound

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

. They use equipment such as super-sensitive microphones to pick up the sounds of firing. By using a combination of surveying

Surveying

See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

 techniques and trigonometry

Trigonometry

Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...

 they then calculate the locations of enemy batteries

Artillery battery

In military organizations, an artillery battery is a unit of guns, mortars, rockets or missiles so grouped in order to facilitate better battlefield communication and command and control, as well as to provide dispersion for its constituent gunnery crews and their systems...

. These results are then transmitted by radio to their own artillery, who used it for targeting.

Sound rangers were used extensively in the Second World War. Many of the officers were former surveyors, estate agents and geographers because of their surveying experience in civilian life. They would be located near the front line but not always among the firing line for their safety.