WWI: Spotting for the Army’s Big Guns I

Using a wireless radio, aerial observers could sometimes adjust the fire of artillery batteries. In this posed photo, the battery commander relays correction information with a megaphone.

The combination of aircraft, modern artillery techniques, and static warfare made the First World War battlefield different than any before. Balloon observers extended the range over which artillery batteries could fire effectively using only ground-based spotters. Airplane crews extended the range farther still, allowing battery commanders to put a pair of eyes directly over targets invisible to both ground and balloon observers.

Army leaders of all nations appreciated the value of effective artillery fire. Converging artillery fire properly observed and ranged offered one army great advantages over another. Commanders could further enhance this benefit if their artillery shells could reach the other force’s rear areas where the enemy had its troops assembled and its munitions and supplies stored. Elevating the observation platform made possible the delivery of long-range artillery fire and led to development of the deep battle, an expanded form of warfare that encompassed more than just the front-line battlefield. The days of generals placing their artillery batteries near the infantry to exchange line-of-sight fire with visible targets had ended.

The heavy artillery duels that developed on the Western Front in the autumn of 1914 forced combatants to settle into opposing trenches and made apparent the importance of the airplane as an instrument of the deep battle. A report on aerial activity dated September 6, 1914, the opening day of the first battle of the Marne, indicates that the German First Army used reconnaissance aircraft in cooperation with its artillery. A British intelligence summary of events on September 25, 1914, complimented the early work of the Royal Flying Corps (RFC), noting “the aeroplanes attached to Corps are directing the fire of our artillery with great success.” Appreciation of the aid artillery commanders received from their aircraft began to spread beyond the command level. German front-line troops who suffered Allied shelling shared the high opinion of the RFC’s work. A letter confiscated from a member of the 242nd Reserve Regiment (XXII Reserve Corps) captured in October 1914 characterized as “wonderful” the British ability to shoot. “I don’t know whether the information is obtained through their aeroplanes, which are always hovering over us,” he speculated, “or whether they have telephones behind our lines.”

Despite such assessments of the British artillery’s accuracy, the earliest attempts to use airplanes to regulate artillery fire suffered from an inefficient communications system. Initial communications practices required pilots and observers to fly away from their observation points to return to the artillery battery or to a command post to drop weighted message bags containing written reports. Time delays proved problematic. Weighted message bags gave way to visual signals—namely light flashes, smoke signals, and wireless messages sent from the airplane—to which batteries responded by displaying cloth panels laid out in pre-arranged patterns. Battery commanders in receipt of signals sent from an airplane vertically over the target computed the target’s position using a clinometer, sextant, or a pair of theodolites. As airplane crews improved their efficiency, artillery officers’ demands for their services increased. Over the winter of 1914–1915, pilots and observers in the RFC’s No. 9 and No. 16 Squadrons experimented with wireless transmitters as part of a continuous effort to improve communications between the artillery and aviation.

While the British Army was learning the basic techniques of artillery regulation in France, their naval colleagues attempting to force the Dardanelles learned from the bitter experience of having effective aerial observation used against them. In March 1915, Hptm. Erich Serno, who later held overall command of the Ottoman Empire’s aviation units, flew the first reconnaissance against the combined British-French naval force that had been assigned to the ill-fated campaign. Serno’s reports aided in the successful artillery defense that kept the Allied ships from getting through the straights and contributed to the British failure at Gallipoli.

Air power historians remember the first major Western Front engagement of 1915, March’s battle at Neuve Chapelle, primarily as the first engagement to make widespread use of aerial photography. Aircrews performed these missions largely for the benefit of the Royal Engineers who used the photos as the basis for up-to-date maps. British forces also used the photos and the maps produced from them in planning the artillery barrage that preceded the battle, a barrage characterized as “the strongest concentration of guns per yard ever assembled, giving an intensity of fire that would not be equaled again until 1917 at Ypres.” Once the active phase of the battle opened, aircraft worked directly with the officers commanding both First Army Artillery Groups, quickly strengthening the relationship between aviation and artillery.

The British high command anticipated that artillery and aviation officers would establish this close working relationship. War Office Memorandum A-1802, issued in February 1915, called for officers at artillery headquarters to issue instructions every evening to airplane observers with whom they were assigned to work the following day in order to outline potential targets identified by that day’s aerial reconnaissance missions. Artillery battery commanders pinpointed potential objectives on a map of the area and then ranged those targets with bracketing fire until their shells fell directly on the mark. For their part, airborne observers signaled corrections to assigned batteries while watching the effect of the fire. When spotting moving targets, such as columns of troops, airplane crews flew over the target and fired smoke signals. Battery crews, in turn, computed their target’s range based on the airplane’s position and altitude.

In the wake of the Neuve Chapelle attack, the Royal Flying Corps updated instructions to its squadrons in the field, issuing more detailed procedures for cooperation with artillery. Experience had taught the RFC that line and range corrections were best made simultaneously. The most significant change in protocol lay in the increased emphasis on the use of wireless, a technological upgrade intended to enhance communications between airplane crews and artillery batteries. Wireless-equipped aircraft could communicate far more quickly and effectively than with previous signaling methods, making it possible for the RFC to change earlier protocols that limited aircraft to working with a single battery. Now, manuals instructed units that, “a highly trained observer in a wireless machine can probably range two batteries on the same target.” Artillery observation crews improvised throughout the early months of 1915 and added valuable experience that informed instructions coming from RFC headquarters. No doubt prompted by that experience, an unknown editor redacted the word “probably” from No. 4 Squadron’s copy of the aforementioned April 1915 manual, removing any uncertainty from the idea an observer could range more than one battery. The British soon upgraded the quality of their artillery maps, marking them with lettered squares inside of which they identified targets by number. Referring to these new maps, battery commanders could direct fire onto target “A-17” or “B-3” further simplifying the communication process between their crews and those manning airplanes.

The most unusual innovation announced by the RFC came in the form of a clock code. Introduced in April 1915, the clock code introduced a new system of communication intended for use between airplane crews and artillery batteries. Using the target as dead center, the pilot or observer directing an artillery shoot affixed a small celluloid circle to his map. The celluloid circle now overlaying the map contained a series of concentric lines marked off in intervals from 50 to 500 yards from the target: circle “A” lay at the 50-yard mark; circle “B” was at 100 yards; circle “C” was at 200 yards, and so on, until one reached circle “F” at the 500-yard mark. Around its perimeter lay numerals corresponding with those on the face of a clock, the numeral twelve representing due north and six due south. Using the clock code, aircraft crews could speak to the artillery battery in shorthand, informing the battery officer that his shot had fallen at “C3,” indicating that the shell had landed two hundred yards due east of the target.

More than two years later, in December 1917, the Royal Navy’s Monitor Spotting Committee considered adoption of the clock code for use at sea by the other half of British aviation, the Royal Naval Air Service. Naval officers endorsed the change because the clock code involved short, easy signals and could be employed for water missions at short notice without the necessity of prior photographs. They too found the clock code offered greater precision than the grid system then in use and, conceding the Royal Flying Corps had more experience in artillery spotting than their own officers, decided to recommend adoption of the Army’s method with some refinement. The Navy’s aerial spotting experience on the Belgian coast demonstrated the clock code’s superiority over the grid system. As members of the Monitor Spotting Committee found, the grid system required preparation of a specific grid for each target where the clock code could be used on any target. Moreover, the clock code required calculation of only one distance as opposed to the grid system that needed two computations. Furthermore, a Navy committee concluded the advantages of systematic uniformity should the two British flying services merge. Seven weeks after its initial meeting, the committee approved changing to the clock code and communicated the new procedures to the Vice Admiral, Dover Patrol, in a letter dated February 21, 1918.

The clock code worked well for airplane crews, but not so well for others involved in the artillery ranging process. Balloon observers and those stationed at high points on the ground could achieve at best an oblique view of the target rather than the near-vertical vantage point necessary to use the clock code. Consequently, British ground and balloon observers continued to use the grid system, necessitating familiarity with both ranging systems for those manning the wireless sets at the artillery batteries. Perhaps preferring to keep artillery ranging as simple as possible, French, German, and American military forces, stuck strictly to the grid system for their own air and artillery crews.

The early months of 1915 saw significant advances in many areas of aerial observation. In addition to wireless transmission coming into general use, enhancements in aircraft, notably the appearance of the French Caudron G.3, improved commanders’ ability to acquire information from close reconnaissance sorties. During these same months pilots and observers on both sides of the lines took the first aerial photos and flew the first successful infantry contact patrols. The wide variety of work performed during artillery observation missions is illustrated by a September 28, 1915 entry in the Royal Flying Corps’ War Diary:

In spite of the unfavorable weather and the difficulties of observing fire, useful work was done by aeroplanes of the 1st Wing on the 1st Army front. Wire cutting by the 21st Heavy Bty ranged by No. 2 Squadron appeared to be successful. No. 3 Squadron ranged the 35th battery on to a heavy gun. Direct hits were obtained by the 33rd Siege battery on a hostile battery ranged by No. 3 Squadron. No. 3 Squadron also ranged the 111th battery on to a hostile battery which was silenced. The 34th Siege battery was successfully ranged on a hostile battery. Numerous explosions appeared in the hostile battery.

Advances in the employment of aviation technology in Europe during 1915 forced skeptics in the US Army to acknowledge its potential importance to battlefield success. Despite having first purchased aircraft in 1909, American army leaders failed until 1916 to confirm their acceptance of the incorporation of aviation strategy into European military doctrine. In a document entitled Military Aviation, the War College Division of the General Staff Corps recommended equipping each American Army division with a twelve-aircraft squadron. The squadrons were to be assigned reconnaissance, artillery observation, bombing, and aerial combat duties.

Aviation’s value to ground operations, particularly the artillery, revealed itself as much when the fliers could not operate as when they could take the air. By the spring of 1915 those planning ground operations understood their plans were likely to suffer when inclement weather prevented aviation operations. A British War Office report written on the Neuve Chapelle battle noted that mist clinging to the ground prior to the battle had prevented air observation for a few days allowing the enemy to take advantage of the situation by concentrating artillery for a counterattack. A similar report on the battle of Festubert noted the start of the battle had to be postponed a day because the weather prevented artillery observation.

As the war neared its first anniversary, commanders continued to refine artillery observation techniques by use of aerial operations. Establishing and maintaining real-time communication between aircraft crews observing the firing and the artillery battery conducting it remained one of the key obstacles to success of the new system. Early approaches involving panel and light signals or written messages dropped from the aircraft, as first practiced at the battle of Festubert, proved inefficient at best. On January 10, 1915, Capt. E. Hewlett and Sgt. Dunn of No. 3 Squadron, RFC, used a signal lamp to correct fire for the 1st Division before being forced to land in the 2nd Division’s area due to engine trouble. The day before, Capt. Hewlett had added a pencil sketch to his report of enemy trenches on the road to La Bassee. In most cases, the ideal of two-way voice communication between the men in the cockpits and those firing the guns was not possible because the combined weight of a transmitter and receiver adversely affected the performance of contemporary airplanes. Under the circumstances, the Royal Flying Corps settled for installing only wireless transmitters. Using their transmitter, airplane crews could signal coded corrections to battery crews. When battery crews wanted to communicate with their partners in the air they used lamp or panel signals. The system worked well enough on June 19, 1915, for Maj. Gen. Hugh Trenchard, general officer commanding the Royal Flying Corps in France, to write to the Deputy Director of Military Aeronautics: “In view of the rapidly increasing use which is being made of wireless telegraphy in connection with the observation of artillery fire from aeroplanes, it has been found convenient to attach an officer having special qualification in this branch of telegraphy to Wing Headquarters.”

Trenchard might have taken a cue from German artillery observation procedures in making his decision to station a wireless officer at wing headquarters. A captured German document, circulated as part of the regular Royal Flying Corps Intelligence Summary a month prior to the announcement of the British air commander’s action, outlined a well-considered protocol for pilots and observers working with the guns, one that incorporated the use of aerial photographs for advance target organization as well as a system of wireless signals. The German procedures called for the air and artillery crews to fix and number their targets in advance using information culled from aerial reconnaissance photographs. Once aloft the pilot and observer signaled “ready to observe” and the number of the first target. After firing commenced the airmen transmitted shorthand Morse code signals indicating “right” or “left,” “long” or “short,” coupled with an estimate of the distance the shell had fallen from the target. No agreed-upon signal existed for targets of opportunity, so if the pilot or observer sighted such a fleeting target he signaled its presence in the clear, e.g. “Hostile battery at 1 km East and 0.5 km North of Marly.” As soon as battery crews located the target on their map and began to fire, the airmen resumed using the established list of signals. The system proved its worth at the end of the first week of the Somme battle, on July 6, 1916:

An aeroplane of No. 9 Squadron reported one Battalion of infantry and a motor transport proceeding from Bois de Leuze to Guillemont. A heavy battery was ranged on this target and seven direct hits were obtained on the column. A number of men were seen to fall and the rest scattered in disorder. A direct hit was also obtained on one of the lorries. The infantry was watched for some time, but were not seen to reform.

The parallel development of aerial observation procedure and wireless technology stimulated each other throughout the war. As spotting became more effective and its use more a routine part of operations, efforts to inhibit the enemy’s artillery became an imperative. The evolution of the fighter aircraft is intimately tied to the need to destroy reconnaissance and observation machines. But while fighters constituted the most glamorous method of limiting the effectiveness of the wireless-equipped artillery spotter, both sides developed other means as well. The German army routinely attempted to jam British, French, and American wireless transmissions and to deceive aerial observers by setting off dummy flashes in the hopes of drawing fire onto non-existent targets. The need to prevent jamming in turn led the British to develop techniques that allowed them to identify enemy wireless stations attempting to jam their signals by both the direction of their transmissions and the musical note of their signal. British air commanders, acting out of fear the Germans might break their codes, also developed alternating groups of signals that aerial observation crews employed during operations.

Friendly radio traffic interfered with artillery spotting nearly as much as enemy jamming. Working together to eliminate or reduce such interference, French and British air commanders developed a coordinated schedule of firing operations so that their transmissions did not overlap. The designers attempted to develop a system that considered every detail, down to the flight time of the artillery shell, which they estimated at 56 seconds.

Wireless technicians found a scientific solution to the problem of friendly local interference in their development of the clapper break. The clapper varied the pitch of a wireless set’s transmission. By the outbreak of the Somme battle in July 1916, reducing radio interference allowed the British to double the number of aircraft working on their areas of the Western Front to a ratio of one wireless aircraft to every 2,000 yards. In a war where artillery had established itself as the primary killer, this proved critically important.

A year earlier, before the war’s first anniversary, British heavy artillery officers were A year earlier, before the war’s first anniversary, British heavy artillery officers were already reporting good results in correcting their fire with the help of aerial observation. In May 1915, they began combining air reports with those received from ground-based observers and intelligence data received from division headquarters. The results proved sufficient for artillery commanders to recommend expansion of the wireless network so that counter-batteries could have their own sections. The organization that grew out of those recommendations tightened cooperation between aircraft, artillery, and the wire telegraphy stations assigned to its batteries, the latter issuing instructions based upon aircraft reconnaissance.

As the war progressed both sides sharpened their artillery observation skills. By the battle of the Somme, army commanders had come to understand the principal value of artillery lay in counter-battery work, or the destruction of the enemy’s artillery. An artillery battery commander’s ability to knock out his opposite numbers depended on maintaining good observation that, as one report confirmed, “in many instances, could only be obtained from the air.” Paul von Hindenburg, part of the duo who replaced Erich von Falkenhayn as commander of all German armies on the Western Front in 1916, commented on the partnership between aviation and the artillery in the aftermath of the German campaign against the French at Verdun. “[T]o engage the enemy’s artillery with the help of aeroplane observers,” he wrote, “is the principal and most effective means of fighting a defensive battle to a successful conclusion. Should this succeed, the enemy’s attack is absolutely paralysed.” In the summer of 1916, the British also took action to guarantee the steady production of well-trained observers by establishing an observers section at its Brooklands Wireless School. The school trained twenty new observers per month.

Counter-battery work assumed such importance that by the launch of the battle of the Somme, more than 40 percent of the British Army’s corps squadrons were committed to this type of work. From the last week in June 1916 until October 20, 1916, British artillery conducted 1,721 operations against hostile artillery, more than six times the 281 actions directed against German trenches. Aircrews did not always have an easy time regulating the artillery. On July 29, 1916, No. 2 Squadron’s 2/Lt. J. B. E. Crosbee and Lt. G. W. Devenish, were working with the 140th Heavy Battery and 2nd Siege Battery, when the 140th refused to fire, likely because a hostile aircraft had been spotted “very high and a long way off.” After the enemy airplane left, the 140th “still refused to fire,” so Crosbee and Devenish tried the 2nd Siege Battery, which fired two shots that landed close, but not exactly on target. By that time, the No. 2 Squadron crew’s B.E.2d was running low on petrol forcing them to return.

The records of No. 34 Squadron, Royal Flying Corps, indicate that during the months of August, September, and October 1916 fully 50 percent of its attempted artillery co-operation missions failed either because of wireless problems or other miscommunications with their assigned batteries, or due to interference by enemy aircraft. Despite these problems, including the growing strength and talent of the German fighter pilots who opposed them, by the end of the Somme battle artillery crews had amassed sufficient respect for the Royal Flying Corps to fight to take control over them.

When the dust settled on the Somme battle, British artillery commanders began to covet direct authority over the aircrews that regulated their guns. Sir Henry Rawlinson, commanding officer of the Fourth Army, endorsed a proposal that would have given the Royal Artillery command of the corps squadrons in all matters except those relating to aviation technology. Fleshing out the idea, Rawlinson suggested that if commanders could find no airmen qualified to serve as artillery observers they should train artillery officers to act in their place. Trenchard vigorously opposed any scheme under which the RFC would lose control of its squadrons, pointing out that the corps squadrons performed more than just artillery observation. The RFC chief also noted that the corps squadrons were not, at that moment, equipped with the type of machines necessary to do all the work the artillery required, especially long-distance photography. Because of their poor livery, corps squadrons would have had to cede jurisdiction over photographic work to fighting units, an action Trenchard would not support. Trenchard also argued the problems the Artillery Corps sought to correct by grabbing control of aviation units were not entirely air-related, citing too frequent changes in the assignment of batteries to aircrews as the cause of much of the trouble.

The inter-service political war over ownership of the corps squadrons soon expanded, drawing other senior officers into the fray and dividing them. Although he supported transfer of control of observation balloons to the Artillery, Maj.-Gen. James F. N. Birch, the artillery advisor at General Headquarters, sided with Trenchard when it came to RFC retention of corps aircraft. Yet Gen. Sir H. S. Horne, commanding officer of the First Army, sided with Rawlinson, maintaining that the Army would not realize artillery’s full potential until “direction and control of artillery fire from the air is placed in the hands of the artillery.” Trenchard dodged the attempted takeover of his air squadrons, though the debate continued with respect to observation balloons.

In the wake of his successful campaign to retain control of his airplanes, Trenchard proposed increasing the size of the RFC’s corps squadrons and doubling their number. He backed up his recommendation with a request that the Army’s brigade commanders estimate the number of airplanes they thought necessary to provide complete artillery coverage throughout days with favorable flying weather. Based on these opinions, Trenchard sought to increase the number of airplanes in a corps squadron from eighteen to twenty-four.

The Royal Flying Corps finalized its evolving artillery regulation techniques based on its experiences during the Somme battle, making only minor improvements over the last two years of the war. In December 1916 the British General Staff published those updated procedures in “Co-operation of Aircraft with Artillery (S.S. 131).”

One of the minor enhancements made following the new guide’s publication involved fine-tuning the zone call system. Since June 1916 pilots and observers noticing fleeting targets were empowered to broadcast a “zone call” to any artillery battery in a position to respond quickly. The zone covered a 3,000-square-yard area. Aircrews calling for fire in a particular zone identified their location by transmitting two letters, the first of which corresponded to the lettered square on the map over which they were flying at the time. The second letter narrowed the fire to a particular zone within the map square. By the end of 1916 so many crews were taking advantage of the opportunity that confusion developed between neighboring batteries. Because adjacent corps used overlapping, identically marked maps and crews transmitted the map square (but not the map sheet) on which they were working, batteries did not always know where they were supposed to be shooting. To solve the problem, on March 24, 1917, General Headquarters issued an amended procedure calling for updated 1:40,000-scale maps printed in alternating sequences divided into squares marked “A” through “D” on one set and “W” through “Z” on the next moving from north to south. On July 24, 1916, the Royal Flying Corps’ War Diary reported “the system of area calls is working very well.” By October 1, the same source noted artillery in the 5th Brigade area cut wire and damaged trenches and that a “heavy accurate shrapnel barrage was brought to bear on enemy trenches during our attack by means of the zone call.” Four days later, No. 4 Squadron’s Lieutenants Dickie and O’Hanlon, “whilst on contact patrol, called for fire on enemy in trenches N. of Thiepval by zone call. Shrapnel was seen to burst over them within two minutes.”

Major A. S. Barrett, commanding officer of No. 6 Squadron, further refined the science of aerial artillery ranging in late 1916 with development of the ringed photograph. Barrett provided his pilots and observers with air photos of their targets marked with concentric circles, marked “Z,” “A,” “B,” and “C,” and with the “N,” “S,” “E,” and “W” compass points. This simple aid reduced distance mistakes crews frequently made in locating the fall of artillery shells. In an early form of battle damage assessment, crews marked on the photograph where the shots fell. Royal Flying Corps Headquarters endorsed the idea and recommended implementation in all British corps squadrons. In an earlier example, on July 18, 1916, Lieutenants Bagot and Peach, on a flash patrol between Armentieres to Bois de Biez in B.E.2c 4162, reported “2 flashes at N.28.A.5.4. (7:40 P.M.) Photo 162,” before having to give up the mission due to low clouds and mist.

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