Sound Ranging in the Great War

Published with Permission by:
Lori S. Tagg, Command Historian,
US Army Intelligence Center of Excellence, Fort Huachuca, AZ.

Private (later Sergeant) Jesse R. Hinman, a native of Astoria, Oregon, arrived on the Lorraine front after three months at the American Expeditionary Forces (AEF) school in Langres, France.  Reaching Mandres on Sunday, March 10, 1918, he was able to watch firsthand the AEF’s 1st Division conduct its first bombardment of the war.  The next day, Hinman’s detachment began its work establishing two forward observation posts, six microphone bases, and a central station all connected by dual lines of communications wire.  Stringing the line was arduous work given the shell-pocked terrain of the area.  Keeping these lines in working order once the German’s launched their Spring Offensive would be even more difficult and hazardous. The detachment’s function, however, was critical to the 1st Division arrayed along the AEF’s sector of the St. Mihiel salient.  Their work was kept highly secret, and the men referred to their unit only by its initials—SRS, Sound Ranging Section.

Hinman was a member of the first SRS to reach the front. By the end of the war, four sections were operational on the American front.  Sound ranging, along with its counterpart flash ranging, was a science new to the battlefield.  Given the static nature of trench warfare over the previous two years, British and French forces had developed and deployed equipment that allowed them to locate enemy guns using sound waves and artillery flashes.  Impressed by the results, General John J. Pershing, commander of the AEF, tasked an officer to study the British and French systems of sound and flash ranging. Simultaneously, the Signal Corps tasked three officers to establish sound and flash ranging companies in the AEF.  The Signal Corps officers and their companies were assigned to Engineer regiments upon reaching France.  However, they operated under the direct tactical command of the AEF G-2.

Each SRS was comprised of a lieutenant, a sergeant, and 39 privates, including linesmen who laid and repaired the communications wires, forward observers on the front lines, and the recorders, computers, and plotters at a Central Station who worked the electrical apparatus.  In simplified terms, the process of locating the position of an enemy gun began with the forward observers stationed on the front lines.  When they heard a significant report by an enemy artillery piece, they pressed a button to activate the recorder at Central Station.  When the sound wave from the report hit a series of six microphones arrayed behind the front line, each microphone sent an electric pulse via communications wire to the recorder.  The recorder documented the exact moments at which the report reached each microphone, similar to the jumps caused by an earthquake on a seismograph.  By plotting the recorded differences in time on a map board, the men at Central Station identified the position of the piece.  Seasoned Sound Rangers could pass the location on to the Chief Intelligence Officer within three to five minutes.  AEF artillerymen could then refine their targeting and conduct a counter barrage to eliminate the enemy’s gun.

As enemy artillery inflicted nearly half of all Allied casualties, the information provided by the Sound Rangers proved to be a significant intelligence source.  In addition to immediately passing on the location of enemy guns, the SRS compiled a daily report for the Artillery Information Service that summarized the class of battery (howitzer or gun), caliber, and probable targets.  Forward observers added their assessments to the report and collected shell fragments, duds, and portions of fuzes for analysis.  The observers’ remarks were critical in many respects.  For example, from their front line posts, observers heard the arrival of German resupply trains.  They also determined that, when the enemy’s band played, new troops were arriving at the front in preparation for an upcoming attack.

The SRS daily reports were compared with information from other intelligence sources, like prisoner-of-war statements, captured documents, and aerial photographs.  As a new science, sound ranging provoked skepticism on the part of many officers who demanded corroboration from other sources, especially aerial photos.  However, sound ranging proved most valuable in locating artillery pieces hidden from visual observation.  In one instance, Sgt. Hinman’s SRS No. 1 had identified the location of a very active enemy battery on the eve of the Battle of St. Mihiel.  Because the information could not be corroborated on an aerial photograph, the sound ranging data was considered an error.  Later it was found that an enemy artillery piece had been hidden in dense woods exactly where the Sound Rangers had indicated.

A post-war study of sound ranging accuracy showed the method could identify the location of an enemy gun within 10-25 meters in ideal weather conditions.  Roughly 80 percent of all battery locations were identified by the Sound Rangers.  Like many new technologies employed during the Great War, sound ranging matured in the postwar period, and by 1927, the function had been transferred from the Engineers to Field Artillery.  The methods continued to be used during World War II, but by that time, sound ranging was being overshadowed by the advent of radar.

Forward observation posts near Forges, France, during World War I.
Forward observers were critical to the effectiveness of sound ranging operations.