In December of 1916, Lieutenant-General Julius Byng, commander of the Canadian Corps, and Major-General Arthur Currie began planning the Vimy offensive operation. Currie grappled with the problem of how to neutralize enemy artillery fire during the assault. In previous Allied operations, enemy artillery had inflicted over half of the casualties suffered by attacking troops. Both Allied and German artillery was primarily employed against infantry entrenchments and troops in offensive and counteroffensive barrages.
The most serious obstacle to the tactical use of artillery against enemy batteries was locating artillery positions, which were situated far to the rear of the trenches. Byng appointed Colonel Andrew McNaughton to the new post of Counter Battery Staff Officer and assigned him the task of locating and targeting enemy artillery positions.
Colonel McNaughton approached Captain Harold Hemming, a Canadian artillery officer who had been serving with the British 3rd Army. Hemming had been working on a method of locating enemy artillery by observing muzzle flashes and using triangulation to calculate their positions. Hemming had informed his senior British commander about his "flash spotting" technique, but his suggestion had been politely ignored.
McNaughton also invited three British scientists to join his staff. The three civilians-Lawrence Bragg, Charles Darwin (grandson of Charles Darwin), and Lucien Bull-had developed a technique called "sound ranging" to locate enemy artillery positions. The process involved a network of listening posts equipped with microphones and oscillographs that recorded the strength and direction of sound waves. The time intervals between listening posts were recorded and then triangulation was used to calculate the exact location of the gun. The British General Staff had ignored the work of these three men, who, consequently, were eager to join McNaughton's staff.
By the end of March, Colonel McNaughton's team had plotted the location of virtually every German artillery battery behind Vimy Ridge.