The Royal Engineers & Armistice Day: Engineering at War.

On 11 November 1918, the guns of the Great War fell silent. That silence was hard-won and it owed as much to engineers, artists and scientists as it did to the infantry.

The Corps of Royal Engineers (RE) hid observers inside man-made replicas of trees, linked aircraft to gun batteries by wireless radio frequencies and turned counter-battery work into a measurable science using sound and light.

These advances were not abstract ideas. They were engineered, tested and risked by people in muddy uniforms, often at night, under shellfire, to get rounds on target faster and bring more soldiers home.

This article celebrates a selection of the achievements of The Corps of Royal Engineers during the First World War.

Contents:

• Who the Royal Engineers Were in 1914-1918
• Camouflage Trees: Observation Without Detection.
• Wireless Technology and Artillery Spotting From the Air.
• Sound Ranging and Flash Spotting: The Science of Counter-Battery Fire.
• The Throat Microphone: Making Pilots Heard.
• Engineering Processes Behind The Innovations.

Who the Royal Engineers Were in 1914-1918.

In 1914, the Corps of Royal Engineers (RE) remit was broad; they were responsible for communication through the Royal Engineers Signal Service, map-making and photography, tunnelling, bridging, field works and battlefield camouflage, as well as much more.

In practice, the Royal Engineers worked as a single system alongside the Royal Flying Corps (RFC), the precursor to the modern-day RAF (Royal Air Force). The Royal Flying Corps aircrew would watch the battlefield from above and, based on their real-time observations, Royal Engineer signallers, surveyors and printers turned those observations into orders, maps and gun corrections.

By 1920, that wartime signalling experience had become a new arm with its own specialisation, the Royal Corps of Signals.

Timeline of Engineering Advancements: 1914 to 1918, from baseline telegraph poles to post-war wireless maturity.

• 1914: The Royal Engineers Signal Service operated telegraph, telephone and visual signalling communications across the trenches. The Royal Flying Corps trialled radio sets for artillery spotting in conjunction with the broader Royal Engineer Corps.

• 1915: The First operational air-to-ground Morse code with wireless technology enabled real-time adjustments to artillery shots and counter-battery fire along the frontline. 

• 1916: First British armoured camouflage tree installed by Royal Engineers camoufleurs. Enabling detailed daytime spotting and providing an early warning of enemy nighttime attacks.

• 1917: Better wireless valve sets and training enabled better communication between the Royal Flying Corps and spotters. Wireless-directed artillery fire became routine and more precise. 

• 1917-1918: The development of sound ranging and flash spotting delivered the first reliable hostile artillery triangulation, enabling accurate counter-battery fire for the first time.

• 1920: Royal Corps of Signals formed from the Royal Engineers Signal Service.

Camouflage Trees: Observation Without Detection

The Human story.

The Problem: In the barren, shattered wasteland of no-mans-land, observation was perilous. A soldier who raised his head above the trench parapet was an instant target for snipers. Yet, without clear observation, artillery was blind and infantry attacks walked directly into hidden machine-gun nests.

The Solution: The Royal Engineers' answer was audacious, borrowing from the French army's idea, to replace a real, splintered tree in no-man's-land with a perfect, hollow, steel-cored replica. This was a task for artists. The Royal Engineers recruited the noted painter Solomon J. Solomon, who assembled a team of sculptors. They would meticulously photograph a target tree, then build its double in a workshop, replicating every knot and scar. The installation was a covert nighttime operation. A Royal Engineer trench party would crawl out, fell the real tree with hand saws and erect the steel version in its place, all before dawn.

The Impact: When morning broke, a lone observer would be inside the armoured tree. Equipped with a periscope, a field telephone and a pocket of boiled sweets, he would sit cramped for hours, watching enemy movements that no aircraft could safely see. His real-time corrections, relayed by telegraph, guided infantry and artillery, saving countless lives.

 

 

The Engineering in plain terms.

Throughout the First World War, camouflage trees were engineered by the Royal Engineers based on real-life examples along the Western Front. They were built as hollow, steel-cored replicas by a team of engineers and artists, then swapped in the dark by felling the real tree and replacing it with the replica.

The realism of the fake trees was paramount; they had to convince the enemy it was the original. As troops spent time in the trenches, no-mans-land (the area between opposing lines) became a barren wasteland and any remaining standing trees, rocks or even large craters became named landmarks. Should anything with the landmark tree look out of place to the regular troops along the line, the spotter would be noticed and eliminated. 

To ensure accuracy, the Royal Engineers enlisted the help of Solomon J. Solomon, a noted British painter during the period, whose work and publications in the press around camouflage techniques came to the army's attention. Following a trip to the front lines in December 1915, Solomon was tasked with the creation of armoured observation posts disguised as trees for the front lines. The first observation post of this kind was erected less than three months later on 22 March 1916.

These engineers and artists who aided the war effort through their camouflage skills eventually took their learnings forward into a new kind of military camouflage workshop. Developments from this area eventually led to decoy tanks and planes during the Second World War.

Wireless Technology and Artillery Spotting From the Air.

The Human story.

The Problem: High above the mud, observers in Royal Flying Corps (RFC) biplanes could see the entire battlefield. They were the army's eyes, but they were mute. A pilot could spot a new machine-gun nest or an enemy battery relocating, but he was powerless to act. By the time he could fly back, drop a message canister and have it relayed, the battle had moved on. This left British guns firing at phantoms, wasting shells and leaving the infantry to walk into threats that had been seen but never reported.

The Solution: The Royal Engineers Signal Service worked to bridge the communication gap. They fitted Royal Flying Corps aircraft with spark transmitters, allowing observers to tap out Morse code corrections. Initially, this was a one-way street; the plane could send, but not receive. 

The breakthrough was a combination of technological advances and strict discipline. By 1917, more advanced valve equipment improved signal clarity and reduced the size and bulk of transmission units. Crucially, crews standardised their communication, using pre-briefed clock codes and grid references instead of long sentences. This streamlined the process, making every transmission count.

The Impact: The communications loop between observer and gunner was closed. What once took an hour of guesswork and signalling could now be achieved in minutes. An observer pilot could see a shell land, tap out a correction and the next salvo would be on target.
This rapid, accurate fire became a routine part of battle plans, allowing artillery to hit fleeting targets and support infantry advances via creeping barrages. This integration of air and ground forces, coordinated by the Royal Engineers, set the foundation for all modern combined-arms warfare.

The Engineering in plain terms.

Early wireless transmission was dependent on spark-gap transmitters. These devices were physically large and heavy, reliant on bulky induction coils and high-voltage power sources. They functioned by creating a high-voltage spark, which generated a powerful but 'noisy' radio signal known as a damped wave. This signal spread across a wide range of frequencies, making it highly inefficient, difficult to tune and prone to interference. These physical and technical limitations, particularly size and power draw, restricted their use in aircraft to one-way Morse code transmissions.

The technological leap came with the thermionic valve (vacuum tube) in late 1917. Unlike the crude 'burst' of a spark-gap, a valve-based oscillator could generate a clean, stable, continuous wave (CW) on a single, precise frequency. This offered superior tuning and signal efficiency. More importantly, valves enabled two-way communication between pilot and ground crew. This single capability made them revolutionary. They were also dramatically smaller, lighter and required less power than spark-gap apparatus, making them far more portable and viable for aircraft integration.

This combination of more portable valve transmitters, two-way communications and new, sensitive receivers made wireless-directed artillery fire a routine and reliable part of field operations for the Royal Flying Corps, Royal Engineers and Royal Artillery.

Sound Ranging and Flash Spotting: The Science of Counter-Battery Fire.

The Human story.

The Problem: A Royal Corps dugout is shelled in the night. Amidst the confusion, chaos and ringing in their ears, the platoon cannot possibly hope to locate the source of the enemy fire to enable counter-artillery action.
That enemy gun battery, hidden miles behind the lines, could unleash a storm of steel on a trench and then simply vanish. This "shoot and scoot" tactic made counter-battery fire a desperate guessing game. A faint flash on the horizon was the only clue, but it wasn't enough. By the time crude calculations were made, the gun crew was already gone, leaving British batteries to shell ghosts and empty mud while the unseen enemy prepared to strike again.

The Solution: The Royal Engineers developed two ingenious, parallel methods.

Flash Spotting: Teams of Royal Engineer observers would position themselves at separate high-ground locations along the frontline as dusk approached. When enemy artillery fired, each spotter would take a precise compass bearing of the muzzle flash. Where their bearings intersected on a map, the gun was found.

Sound Ranging: A Royal Engineers sapper team would lay an array of five to seven microphones across several kilometres, all wired to an oscillograph in a dugout. When enemy artillery fired, the tiny time difference between the "boom" arriving at each microphone was recorded. Using formulas developed by physicist William Lawrence Bragg, soldiers could calculate the gun's exact coordinates.

The Impact: When combined, these two methods were lethal. Flash spotting provided the bearing and sound ranging provided the distance. Enemy guns could be fixed to within tens of metres, fast enough for friendly artillery to return accurate fire before the enemy crew could relocate. Royal Engineers meteorologists even applied corrections for wind and temperature to increase accuracy. For the first time, counter-battery fire became a measurable science, allowing commanders to systematically find and destroy the enemy's most powerful weapons.

The Engineering in plain terms.

Flash spotting, used several observation posts on surveyed points with clear horizons, each with a theodolite or alidade and a field telephone to a central plotting room. When a muzzle flash appeared, observers using synchronised watches called the exact second and an azimuth; plotters drew those bearings on large-scale maps, matched simultaneous reports to the same shot, applied small instrument and map corrections and took the intersection as the enemy artillery position.

Sound ranging arrays typically used five to seven condenser microphones spread over several kilometres, typically 1400m between each, with a wired connection to the base and a drum-paper recorder similar to a modern-day seismograph for measuring earthquakes.
The time difference between the first microphone picking up the muzzle blast and each subsequent microphone would be used with Lawrence Bragg's formulas to provide distance ranges to enemy batteries.
The Sound-Ranging crews calibrated their microphone arrays using the known position of friendly artillery test-firing each day along the line. Using those audio recordings as a base for distance, they then cross-checked these test-firing measurements against aerial photographs from the Royal Flying Corps. 

Utilising the flashes for bearing, sound for range and meteorology for wind direction, these methods let commanders plan and time attacks with far more confidence thanks to accurate counter-battery fire.

The Throat Microphone: Making Pilots Heard.

The Human story.

The Problem: In the open cockpit of a biplane, the overwhelming roar of the engine and the rush of the slipstream made speech impossible. A standard mouth diaphragm-microphone was useless; it picked up more wind than voice. For air-to-ground radio to be truly effective, pilots needed a way to be heard clearly.

The Solution: The solution came from Charles Edmond Prince and a small Royal Engineers team. Their invention, the laryngophone (or "throat microphone"), bypassed the air completely. It was a form of contact microphone that picked up vibrations directly from the user's throat. By placing twin contact pads on the pilot's larynx, the system captured the vibrations of speech while inherently rejecting the airborne noise of the engine and wind. By 1918, this was integrated into a hands-free version inside the flight helmet.

The Impact: The result was transformative. Pilots could finally speak. An observer could call out corrections like "short 50, right 2" in a clear voice without taking his hands off his controls or map. This dramatically improved the speed and accuracy of artillery spotting, reducing wasted shells and the time aircraft spent in dangerous airspace. This Royal Engineering Corps innovation set the standard for all future aviation and armoured vehicle communication systems, where a clear voice in a high-noise environment is critical.

 

The Engineering in plain terms.

The laryngophone picked up vibration directly from the throat rather than airborne sound. Development ran from 1915 to 1918 under Charles Edmond Prince, involving the Royal Engineers’ Signal Service and Marconi engineers working at Brooklands aerodrome and the Admiralty Signal School, along with Marconi’s Chelmsford workshops.
Early prototypes were simple single-pad contact mics held under a scarf or elastic strap; they often shifted position, giving weak or distorted speech. Next came paired pads mounted on a sprung yoke, improving contact and consistency when the pilot turned his head. Later iterations integrated a small valve amplifier so the weak throat signal could be boosted before modulation.
The final refinements involved sewing both the pick-ups and the ear receivers directly into the flight helmet, giving a hands-free system that stayed in place during manoeuvres and slipstream buffeting. By 1918, trial squads in France were flying with these integrated sets as standard. The design pattern carried forward into the early Royal Air Force and then into Second World War aircrew communications.

The result was intelligible speech at open-cockpit speeds and a practical two-way voice link for artillery cooperation, reconnaissance control and training.

 

Engineering Processes Behind The Innovations.

These four stories share a pattern. Cross-disciplinary Engineering teams that spoke each other’s language. Rapid trials and iteration with honest feedback, coupled with field fixes that became standard practice across the front line. Artists and sculptors who learned about camouflage, along with physicists who developed methods of range-finding using microphones and acoustic mathematics. 
Requirements were gathered at the front by the Royal Engineers, prototypes built in the reserve trenches, then deployed and iterated upon. This process of engineering continued until solutions worked for the people who carried them, worked on them and depended on them for survival on a daily basis.

Necessity is the mother of invention, but without the skills and organisation of the Engineers involved, none of this would have been possible.

Legacy and Post-1918 Impact.

These efforts left a clear legacy for the twentieth century and beyond.
Signals experience inside the Royal Engineers led directly to the creation of the Royal Corps of Signals in 1920. Camouflage moved from ad hoc artistry to a disciplined practice, scaled in later wars and now studied as a science in its own right. Sound ranging and flash spotting set the pattern for modern counter-battery work and influenced peacetime acoustics and geophysics. Finally, throat microphones, proven in service, became standard across aviation and in armoured vehicles.

The thread that ties these together is human. Ingenuity under pressure, teamwork across trades and a clear aim to protect lives while achieving the mission under some of the most dire circumstances humans have had to endure.

In the spirit of remembrance, progress in engineering did not remove the cost of war, but it reduced needless loss and brought the armistice closer.

This remembrance month, as we remember the contributions of Soldiers, Engineers, Artists and ordinary people who answered the call of service, please consider donating to the Royal British Legion's Poppy Appeal below.  

Donate To the Poppy Appeal Today.

 

FAQ's

Q: Who managed battlefield communications before 1920?

A: The Royal Engineers Signal Service handled telegraph, telephone, visual signalling and later wireless. In 1920 this became the Royal Corps of Signals.

Q: How did camouflage trees actually help soldiers?

A: They let observers watch the dangerous ground without exposing their heads above the parapet. Their reports guided artillery and warned infantry before they moved. They also sometimes operated as nests for snipers, but this was less frequent.

Q: How did wireless spotting change the pace of battle?

A: It shortened the loop from observation to correction. Batteries used fewer rounds to find the target and could engage fleeting threats beyond direct sight.

Q: What is the difference between sound ranging and flash spotting?

A: Flash spotting is optical. Sound ranging is acoustic. Used together, they gave battery-level locations that enabled accurate counter-battery fire.

Q: What exactly is a throat microphone?

A: A laryngophone picks up vibrations from the throat. It improves speech intelligibility in loud, windy cockpits and lets crews keep their hands on the controls. It is a form of a transducer microphone, converting one form of energy into another.

Article Sources:

Sources: IWM (fake trees); IWM Collections (camouflage tree, Mar 1916); Marconi Heritage (wireless in the air); IEEE Spectrum (RFC wireless phones); 1914–1918 Online (artillery location); APS News (W.L. Bragg, sound ranging); Van der Kloot (Bragg on sound-ranging); National Army Museum (Royal Corps of Signals); Royal Signals Museum (Signals Service, formation); Western Front Association (aerial photography); The National Archives (WWI telecommunications).