The definitive source on the history of artillery sound ranging through WWII is Hercz, "Development of the Field Artillery Observation Battalions". He says: "T

The definitive source on the history of artillery sound ranging through WWII is Hercz, "Development of the Field Artillery Observation Battalions". He says: "The first officially recognized experiments in sound ranging started in September 1914, when a professor of astronomy from the Paris Observatory was given leave from service at the front to work on this new idea. In Paris he consulted with Lucien Bull of the Marey Physiological Institute... On November 17, 1914, various systems were tested at a base laid out at the Marey Institute. Two guns firing from 4 kilometers away were located within about 50 Meters." He also credits Ernest Esclangon of the Bordeaux Observatory with discovering that the microphones needed to filter out the high frequency sound of the shell in flight and listen only to the low frequency sound of the gun wave. And he adds, "The Germans expedited the work by conveniently moving the front lines to the suburbs of Paris, where the scientists could readily travel between the laboratories and the ultimate proving ground of combat areas."