Tunnelling companies of the Royal Engineers

Royal Engineer tunnelling companies were specialist units of the Corps of Royal Engineers within the British Army, formed to dig attacking tunnels under enemy lines during the First World War.

The stalemate situation in the early part of the war led to the deployment of tunnel warfare. After the first German Empire attacks on 21 December 1914, through shallow tunnels underneath no man’s land and exploding ten mines under the trenches of the Indian Sirhind Brigade, the British began forming suitable units. In February 1915, eight Tunnelling Companies were created and operational in Flanders from March 1915. By mid-1916, the British Army had around 25,000 trained tunnellers, mostly volunteers taken from coal mining communities. Almost twice that number of "attached infantry" worked permanently alongside the trained miners acting as 'beasts of burden'.

From the spring of 1917 the whole war became more mobile, with grand offensives at Arras, Messines and Passchendaele. There was no longer a place for a tactic that depended upon total stasis for its employment. The tactics and counter-tactics required deeper and deeper tunnelling, hence more time and more stable front lines were also required, so offensive and defensive military mining largely ceased. Underground work continued, with the tunnellers concentrating on deep dugouts for troop accommodation, a tactic used particularly in the Battle of Arras.

Background
In siege warfare, tunnelling is a long-held tactic for breaching and breaking enemy defences. The Greek historian Polybius, in his Histories, described accounts of mining during Philip V of Macedon's siege of the town of Prinassos; there is also a graphic account of mining and counter-mining at the Roman siege of Ambracia.

Mining was also a method used in siege warfare in ancient China from at least the Warring States (481–221 BC) period forward. When attackers attempted to dig tunnels under walls for mining or entry into the city. The defenders used large bellows (the type the Chinese commonly used for heating up blast furnaces for smelting cast iron), to pump smoke into the tunnels in order to suffocate the intruders.

In 1215 during the First Barons' War, John, King of England laid siege to Rochester Castle. Eventually, he ordered his troops to dig a tunnel under the south tower, which they held up with pit props. After the tunnellers lit the props, the tower fell down, ending the siege even though the castle's main walls remained standing.

In 1346, Edward III of England requested that miners from the Forest of Dean, Gloucestershire accompany his expedition to France, during the first part of the Hundred Years' War between England and France.

The Corps of Royal Engineers were formed in 1717. In 1770, the Company of Soldier Artificers formed a specialist tunnelling troop in Gibraltar to dig defensive positions into the Rock.

During the Siege of Lucknow in 1857, Royal Engineers were asked to undertake counter-mining.

World War I formation


By the end of May 1915, a continuous opposed pair of defence-in-depth trench earthworks with no vulnerable flanks, stretched from the North Sea coast to neutral Switzerland. With both sides equally well dug-in and deploying comparable troop numbers and armaments, neither was to prove strong enough to force a decisive breakthrough.

The resultant static warfare meant that tunnelling saw a brief resurgence as a military tactic. As in siege warfare, mining was possible due to the nature of the fighting. Secondly, the ground on the Western Front was a prime candidate for underground warfare.

Although the British were equipped with Royal Engineers who were trained in carrying out sapping, mining and tunnelling operations, there was no core team of specialist skills.

Request and proposal
Even before it became apparent that the Germans were mining to a planned system, the commanding officer of the IV Corps, Sir Henry Rawlinson, requested the establishment on 3 December 1914, of a special battalion to assist with mining duties. Towards the end of 1914, the civil engineering company of MP and British Army Major, John Norton-Griffiths, was working on sewerage renewal contracts in Liverpool and Manchester. The relatively small-bore tunnels were being driven by a manual technique known as "clay-kicking." Only useful in firm clay soils, the man doing the digging sat with his back supported by a wooden frame, with his feet pointing towards the cutting face. With a spade-like tool he dug out the clay, passing the spoil over-head to one of his mates for disposal at the rear. In early December 1914, Norton-Griffiths wrote to the War Office suggesting that the technique would be useful within the war effort for attack, spying or for intercepting German tunnels coming in the opposite direction. He concluded by asking to be allowed to take a group of his "moles" to France where if the soil was right, they could quickly undermine enemy positions. His letter was filed.

On 20 December 1914, by placing shallow tunnels through no man’s land, German sappers placed eight 50 kilogramme (110 lb) mines beneath the positions of the Indian Sirhind Brigade in Givenchy. Following their simultaneous detonation, an infantry attack resulted in the loss of the entire company of 800 men.

Kitchener responds
Following further attacks, it was evident by January 1915 that the Germans were mining to a planned system. As the British had failed to develop suitable counter-tactics or listening devices, Sir John French, commander of the British Expeditionary Force, wrote to the Secretary of State for War, Lord Kitchener, describing the seriousness of the German mining situation.

Norton-Griffiths received a telegram on 12 February 1915, instructing him to report to the War Office. On his arrival, he was shown into Kitchener's private offices, where he (Kitchener), showed him French's letter. Kitchener then asked Norton-Griffiths for his advice, to which using a coal shovel from the room's fire grate, he sat on the floor and gave a demonstration of "clay-kicking."

Impressed but sceptical, Kitchener asked Norton-Griffiths to travel that day to France to communicate his method to the commanders there, and confirm the suitability of the Flanders soil. If positive, he would then raise a suitable battalion of "moles", as Norton-Griffiths had named his new teams, the same name as their civil engineering counterparts.

Arriving with two of his employees at the GHQ Saint-Omer office of the Engineer-in-Chief (E-in-C), Brigadier George Henry Fowke, on 13 February, Norton-Griffiths gave another demonstration of "clay-kicking." A sceptical Fowke instructed his assistant, Colonel Harvey, to take Norton-Griffiths and his employees to Army and Corps headquarters on 14 February, to see what the Corps of Royal Engineers thought of the idea.

In an early public relations exercise, on 14 February, Norton-Griffiths got Colonel Harvey to stop at four headquarters – Army, Corps, Division and Brigade. At each briefing, Norton-Griffiths repeated his demonstration. On arrival at the front line, (a mile from where the first German mine had exploded the previous December), they confirmed the excellent conditions of the clay-based soil and returned to St Omer via the four headquarters to communicate their findings.

The following day, the team held further meetings in St Omer, concluding with a meeting between Norton-Griffiths, Fowke and Sir John French, the C-in-C, for a personal explanation. Fowke gave his agreement to a trial to which French agreed, and the three set out a structure for what were to be called tunnelling companies, rather than Norton-Griffiths' preference for 'moles': a symbol which many of the tunnelling companies would later adopt as their unit sign.

In a meeting with Lord Kitchener on 17 February, he reported on his visit to France and the agreement of Collins and Fowke to form trial tunnelling companies. Norton-Griffiths pointed out that to deploy the units at the speed which Lord Kitchener had suggested, would require the recruitment of civilians, who could not undergo basic military training to enable their immediate deployment to the front line. Kitchener's staff were highly sceptical of the proposal, but using his carte-blanche skill to cull such skilled men from regular infantry units, Norton-Griffiths won his argument.

First tunnelling companies
Norton Griffiths travelled to Liverpool on 18 February and closed down one of his tunnelling contracts, making 18 staff redundant. The following day the War Office gave its approval to the Royal Engineers tunnelling company scheme. On the same day, 18 formerly redundant Liverpool men turned up in Chatham to be enrolled, clothed and turned into Royal Engineers. One of the most rapid acts of the First World War, men who were working underground as civilians on 17 February, were working underground on the Western Front by the following Monday, a mere four days later.

The first nine Royal Engineer Tunnelling Companies, numbers 170 to 178, were each commanded by a regular RE officer – they comprised: 5 officers and 269 sappers, aided by temporarily attached infantrymen as required, (which almost doubled the companies number). Norton-Griffiths, in the rank of major, acted as a liaison officer between these units and the E-in-C's office in St.Omer.

Although able to select almost any soldier he wished, as he had predicted, Norton-Griffiths was quickly forced to recruit civilians. The new recruits in these units, aged anything up to 60, did not readily conform to military discipline and Norton-Griffiths' skills as a politician and as an engineer were called on in recruiting the men he needed and integrating them into the military environment. His judgement of people was remarkably accurate, he very rarely made a mistake in selecting men for a commission.

The deployment of the first eight units led to the introduction of the tunnelling method that allowed the British to dig tunnels at a rate of 8 m per day, compared to the Germans' 2 m.

First action: Hill 60, Ypres Salient
First deployed in the Ypres Salient with the 28th Division, the specialist tunnelling companies laid six mines by 10 April 1915. These mines (together with others that were unfinished), were filled with around 10000 lbs of Ammonal explosives, the resulting explosions ripping the heart out of Hill 60 over a period of about 10 seconds. The effect was a mini-earthquake that split the ground under the entire hill, white flames shot 300 ft into the sky. Concrete pillboxes and soldiers occupying them came down in all directions 300 yd away. The explosion resulted in a 70 ft deep crater, with surrounding trenches sandwiched shut so fast soldiers were crushed still in their standing positions. The Germans all around were crying with fear. Many retreated in terror, the-then tunnel master, Otto von Fusslein, was castigated, although the position was quickly recaptured a few days later.

The action showed the importance of the necessity for a counter-offensive against aggressive German mining on the British lines. Having proven the system, Norton-Griffiths left the company and returned to London in April 1916 and his duties as an MP. He left GHQ with his rough plan of August 1915 for extensive mining on the Messines front, which formed the framework on which mines were used at the Battle of Messines two years later. He was awarded the DSO for his efforts, mentioned in dispatches three times and promoted to Lieutenant Colonel in 1916.

Expansion
The success of the Tunnelling Companies led to mining being made a separate branch of the new E-in-C's office, which was under Major-General S.R. Rice and the appointment of an Inspector of Mines at GHQ.

The second group of tunnelling companies were formed from Welsh miners from the 1st and 3rd Battalions of The Monmouthshire Regiment, who were attached to the 1st Northumberland Field Company, Royal Engineers, a Territorial unit. Twelve Tunnelling Companies were ultimately formed in 1915 and one more in 1916. A Canadian troop was formed from men on the battlefield, plus two other companies trained in Canada and then shipped to France. Three Australian and one New Zealand tunnelling companies were formed by March 1916. This resulted in 30 companies by the end of 1916, many made up of ex-miners.

All of these companies were occupied on other underground work such as the digging of subways, saps (a narrow trench dug to approach enemy trenches), cable trenches, underground chambers for such things as signals and medical services, as well as offensive and defensive mining.

Methodology
Both sides deployed tunnelling, with the German lead quickly followed by the British follow-up. The result was a labyrinth of tunnels within a cat and mouse-like game of tunnelling, counter-tunnelling and counter tactics. As the tactics and counter tactics deployed against each other became less and less effective, the depth at which the tunnels needed to be dug became deeper and deeper and hence more dangerous. The result was a greater time to dig, resulting in a greater vulnerability to both leakage of information and tunnel collapse, and a higher loss of lives in the most hideous of circumstances: entombment, drowning, gassing or obliteration in cramped and claustrophobic galleries beneath no man’s land.

Recruitment
To make the tunnels safer and quicker to deploy, the British Army enlisted experienced coal miners, many outside their nominal recruitment policy. The desperate need for skilled men saw notices requesting volunteer tunnellers posted in collieries, mineral mines and quarries across South Wales, Scotland and the Northeast of England covering Derbyshire, County Durham, Nottinghamshire and Yorkshire. In addition, specialist tin miners were also recruited from the Cornish mines mainly joining the 251st Company RE. To attract the tin miners, a per diem of six shillings a day was offered to underground miners, which was around double to that was being paid in the mines.

The mining assistants who acted as 'beasts of burden' were often made up of "Bantams", (soldiers of below average height who had been rejected from regular units because they did not meet the height requirements). Upon the declaration of war in August 1914, William Hackett applied and was turned down three times at the age of 41 by the York and Lancaster Regiment. On 25 October 1915, despite having been diagnosed with a heart condition, he was enlisted and sent for two weeks basic training at Chatham, joining 172 Tunnelling Company.

Digging
As tunnels were vulnerable to attack, the entrances were a closely guarded secret. With electricity in short supply in the frontline, tunnellers were forced to work by candlelight. Operating in near silence to avoid detection, the tunnels were cold, cramped and often up to a foot deep in freezing water.

Tunnel entrances were most often at the bottom of deep shafts. From here, using the clay-kicking technique, the tunnels were aligned and given direction by the simple use of candlelight. They were built on a slight uphill gradient of between 1:100 and 1:50 to keep them as dry as possible. This meant that they were also vulnerable to the accumulation of gas at the digging face.

A clay-kicking team typically consisted of three men: a "Kicker" who worked at the face, a "Bagger" who filled sandbags with the lumps of clay spoil, and a "Trammer" who transported the bags out of the gallery on a small, rubber-tyred trolley on rails. The trolley was also employed to bring timber in on the return journey.

If the tunnel was long, the trammer was given extra assistants, to speed the exit of spoil and intake of timber. The team was responsible for its own safety, and would insert a 'sett' of wooden supports every 9 in. As no nails or screws could be used due to noise, the 'setts' (consisting of a sole, two legs and a cap), were sawn with a rebated step, which once trimmed into the clay, would expand with the absorbed water into a solid structure.

Working conditions
Working in cold, cramped conditions, miners worked in 6 or 12 hour rotating shifts. Miners were prone to illness, with high rates of trench foot and bad food disease, while fatigue compounded the situation, creating a high mortality rate. The miners also had to cope with difficult circumstances when they entered the mining tunnels. Often the tunnels were dark, small and flooded with water. Tunnellers were billeted quite a long way back from the front line, while a regular Royal Navy-style rum ration was issued to keep out the cold.

Natural gases and gases given off as a result of explosions could ignite, poison or asphyxiate. The major problem gas for tunnellers was carbon monoxide, given off by all projectiles from shells to rifle bullets.

With the use of experienced miners, came the use of "miners friends" in the form of mice and later small birds, such as canaries. With a high metabolic rate, they were readily susceptible to gas, and issued to the Tunnelling Companies as an official item. When gas was present, their unconsciousness would alert miners to the need to evacuate. Although many animals died, they could recover on the surface, with at least one company keeping a record of the gassings so that their creatures did not have to endure more than three instances before being pensioned off to an aviary. The role of the miners friends are honoured on the Scottish National War Memorial in Edinburgh.

In extensive tunnelling systems, air-tight doors were introduced to control air flows.

Mines Rescue
Such was the reliance on mining during the early stages of the war, that eventually mining-related casualties became so great that the War Office decided something had to be done. The skilled mining volunteers were particularly hard to replace. In one six-week period, one tunnelling company had 16 men killed; 48 sent to hospital; and 86 minor cases treated at the shaft head and returned to company billets. Another company suffered 12 men killed by gas; 28 sent to hospital in one month; 60 minor cases were retained with the unit.

In response the affected mining units put out an urgent call for appropriate rescue equipment. Captain D Dale Logan was appointed advisor to GHQ in September 1915 on all matters connected with the health of the specially enlisted Tunnelling Companies.

In June 1915, Lance Corporal Arthur B. Clifford was made solely responsible for mine safety training. Sent to the front to train 3000 mine-rescue troops in a month, there were only 36 sets of 'PROTO' breathing equipment available in the whole of the United Kingdom. Clifford was based with the Royal Engineers at Strazeele, with a sub-station at Berguette. This became the first Army Mine-Rescue School. Clifford was awarded the Meritorious Service Medal in 1917 for what he had achieved.

From July 1916, under Logan's new organisation, the second Army Mine-Rescue School was established at Armentieres. This allowed the British to deploy a system of mines rescue, where no mining shaft was further than 200 m from a rescue station. Named after the kit they employed, Proto-men were hand-picked experienced miners, selected for coolness under pressure. Two men were on duty at all times, with additional access to 10 electric miners lamps, six canaries, four mobile cages, one saw, one hand axe, three life-lines, two mine stretchers, one trench stretcher, one Primus stove, two tins of café au lait, six hot water bottles and six blankets.

Underground fighting
As a result of so much mining activity by both sides, detection and breakthrough into each other's tunnelling systems occurred frequently. The result was often the deployment of the emergency camouflet, a pre-prepared charge which was always ready in the British and Allied forces sectors when tunnelling was taking place. Vicious hand-to-hand fighting in the dark with picks, shovels and wood used as weapons might also take place. Although all miners were trained to use rifles, the restrictions of tunnel construction and the conditions of the tunnels where the miners had to operate often meant they could not be used. If the opposing side were unsuccessful in repelling an attack, then enemy tunnels could be used for short periods to observe enemy tunnelling activity and direction.

Listening
Early tunnelling required a great deal of improvisation, as equipment was in short supply. This made tunnels shallow, the noise of digging being detectable using simple devices in the trenches, even amongst the gun-fire.

In the trenches, soldiers found that driving a stick into the ground and holding the other end between their teeth enabled them to feel any underground vibration. Another method involved sinking a water-filled oil drum into the floor of the trench, with lookout soldiers taking turns to lower an ear into the water to listen for vibrations. Improvised methods later included Water Board inspector short-sticks, each with a single vibrating wire-type earphone attached, or using filled French water-bottles laid flat on their sides in pairs, so they could be listened-to through medical stethoscopes.

Underground, within the tunnelling operations, side-shaft listening posts were deployed and manned by soldiers whose job entailed listening for indications that the enemy was tunnelling. Initially using just manual methods, the British were eventually equipped with the Geophone, which could detect noises up to 50 m away. Employing two Geophones, a listener was able to ascertain the direction of hostile activity by moving the sensors until sound levels were equal in both ears. A compass bearing was then taken. When gauging distance only, both earpieces were plugged into a single sensor; this was a skill only gained by experience.

Deploying listeners in different tunnels in triangulation techniques, by the end of 1916 the scale of British tunneling warfare had expanded to such an extent that there were not enough listeners to man every post; central listening stations were devised. Working electronically like a telephone exchange, the signals from up to 36 remote sensors (Tele-geophones and Seismomicrophones) could be distinguished and logged by just two men.

Underground tactics
The tunnellers developed counter tactics, which both sides deployed. The first was the use of large mines placed in one's own tunnels – some actually dug towards enemy noise to create damage – which when exploded would create fissures and cracks in the ground, making the ground either unsuitable for tunnelling or destroying existing tunnels and works. A small device, called the camouflet, created a localised underground chamber designed not to break the surface and form craters, but to destroy a strictly limited area of underground territory – and its occupants.

The second tactic, deployed when the enemy tunnel was too close to your existing works or trenches, was the deployment of rod-fed torpedo shaped camouflet charges. Effectively land mines on the end of long iron sticks, the technique was a defensive tactic against an immediate threat. Towards the end of the tunnel war, forces also deployed mines at greater depths, which together with listening devices could be exploded away from friendly trenches as a defensive measure.

British advantages
The British tunnellers had three advantages over their German counterparts, the Pioniere:

Firstly, the British used clay-kicking which was a virtually silent method of tunnelling. The Germans did not know of this technique, having not used it in their pre-war civil engineering, and thus used mattocks (a type of pick-axe) and other loud tools throughout the war. This made their tunnels more vulnerable to detection and attack.

Secondly, the use of clay-kicking made the British four times as fast at tunnel digging as their German counterparts.

Thirdly, British positions were most often located in low-lying areas, while German positions tended to be more elevated. Although this made the British more vulnerable to shelling, it also meant that British tunnellers had less of the soft quicksand-like 'Kemmel Sands' (known to the Germans as schwimmsands), an integral component of the geological make-up of the ridges around Ieper (Ypres), to penetrate. While the bottom blue clay layer was virtually flat, as was the Kemmel Sands that sat on top of it, there was a dry strata which varied above this which created the geographical contours. This varying dry strata increased pressure on the Kemmel Sands, which unable to egress water below them, made them wet and unstable. When punctured, the Kemmel Sands would often "spout" under pressure, both water and solid material. Difficult to dig through and keep the mining wooden structure stable, the Germans, assuming that the British had the same instability problem, dug few tunnels until 1916. The British found an engineering solution by creating a metal tube through the Kemmel Sands. Sunk either through its own weight or by the use of hydraulic jacks, once the blue clay layer was hit, the tunnelling could again resume under wooden supports.

The British used tube shafts from May 1915, a full year before the Germans, who when they did start to use metal and concrete tunnels, had lost the strategic advantage and were digging purely for defensive purposes.

Operations
Tunnelling companies were not popular amongst the ordinary troops. Knowing such a unit was nearby made them nervous:
 * Danger from above the ground (from the enemy)
 * Danger from below the ground (from their own and enemy tunnelling companies)
 * If the enemy knew a tunnelling company was in the area, it made the trench troops a more likely artillery target. This was further emphasised as the war developed with both sides using larger and larger mines, often deployed ever-closer to their own trenches. These were more likely not to be detonated on time, or if they did, shower debris over their own trenches and advancing troops, causing increased casualties.

The first British mine to be detonated was at Hill 60 on 10 April 1915. Mines were also used at The Bluff, St Eloi, the Battle of Aubers Ridge in May 1915; Hooge, Givenchy, Cuinchy and the Battle of Loos in September 1915.

Battle of Mont Sorrel
Hooge, a small village in the Ypres Salient in Flanders, was the site of a château which changed hands a number of times. Used as the Divisional Headquarters for the area, the staff at the château from the 1st and 2nd Divisions were all killed when the château was shelled on 31 October 1914. German forces attacked the château between 24 May and 3 June 1915 and despite the detonation of a British mine by the 3rd Division, leaving a massive crater, took control of the château and the surrounding area on 30 July. The château and the crater (craters being strategically important in relatively flat countryside), were taken by the British 6th Division on 9 August. It was reclaimed by the Germans on 16 June 1916 and retaken by the British on 31 July 1917 when the 8th Division managed to advance past it by about a mile. The Germans retook the site in April 1918 as part of the Spring Offensive but were expelled from the area by the British on 28 September as the offensive faltered. The chateau was completely destroyed along with the entire village; several large craters were blown over the course of the 1917 fighting.

Battle of the Somme


When the Battle of the Somme started on 1 July 1916, the plan was to detonate ten mines, the northernmost of which was that under the Hawthorn Ridge Redoubt, a front-line fortification west of the village of Beaumont Hamel. The other two were the Lochnagar mine and the Y Sap mine at La Boisselle. The Hawthorn Ridge Redoubt mine, which consisted of 40000 lb of explosives, was the first to be detonated. The plan was to detonate the remainder at 7:28 am, two minutes before Zero hour, when the infantry advance would begin, but a compromise was reached with Lieutenant-General Aylmer Hunter-Weston, whose VIII Corps was holding the Hawthorn Ridge sector, enabling him to explode the mine at 07:20. This led to the successful filming of the explosion by British cinematographer Geoffrey Malins, who was filming the 29th Division's attack. He had his camera set up about 0.5 mi away, trained on the ridge and waiting for the explosion.

Tunnelling units involved in the Battle of the Somme were the 174th, 178th, 179th, 181st, 183rd, and 252nd companies.

Battle of Messines


In January 1917, General Sir Herbert Plumer, gave orders for mines to be placed under the German lines in preparation for the Battle of Messines.

From 1915, British engineers started digging, but it was not until the winter of 1916 when they were joined by Canadian, Australian and New Zealand engineers, that mass tunnelling started under the German trenches. Twenty-two mines were dug, some up to 2160 ft long and up to 125 ft deep, altogether containing 600 tonnes of ammonal explosive. To solve the problem of wet soil, the tunnels were dug in the layer of "blue clay", 80–120 feet (25–30 m) below the surface. The galleries dug in order to lay these mines eventually totalled over 8000 yards in length, and had been constructed in the face of tenacious German counter-mining.

On several occasions, German tunnellers were within yards of large British mine "chambers." The mine at Petite Douve Farm was discovered by the Germans on 24 August 1916 and destroyed by a counter-mine. Two mines close to Ploegsteert Wood were not exploded as they were outside the attack area.

As preparation for the attack, six mines were detonated on 27 March 1916. The largest of these was at St Eloi, dug by the 1st Canadian Tunnelling Company, consisting of 95600 lb of explosive. This allowed the capture of St Eloi by the British 41st Division.

This choice reduced the total explosive to 450 tonnes. The evening before the attack, General Plumer remarked to his staff, "Gentlemen, we may not make history tomorrow, but we shall certainly change the geography." With doubts about the reliability of the system, (some mines had been lying underground for over a year), soldiers waiting in the trenches had been warned that they could not depend absolutely on the mines working as planned, so their orders were to leave their trenches and attack whether the mines exploded or not. The explosion of the mines took place at 03:10 on 7 June. Approximately 10,000 German troops were killed when the 19 mines were simultaneously detonated, creating an explosion so loud it was heard by British Prime Minister David Lloyd George in his study in 10 Downing Street in London. There is even a report of an insomniac student hearing it in University College, Dublin.

The largest of the 19 Messines mines was at Spanbroekmolen. Found and counter-mined by the Germans a few weeks before the attack, the British were forced to dig a second entrance tunnel into the already prepared explosive chamber, (which consisted of 41 tons of ammonal explosive 88 ft below ground), to reconnect the detonation wires. Although tested fully just a few hours before the attack, officers used torch batteries to prove the circuits. As instructed, soldiers of the 36th (Ulster) Division had already left their trenches and begun to move across No-Man's Land when the mine exploded a few seconds late, leading to some being killed by falling debris. They are buried in Lone Tree cemetery nearby. The "Lone Tree Crater" formed by the blast was approximately 250 ft in diameter, and 40 ft deep.

The 1st Australian Tunnelling Company took over mining operations in November 1916 on Hill 60, led in part by Capt. Oliver Holmes Woodward. The explosion demolished a large part of the hill, killing many German soldiers.

The British intended to dismantle the two remaining mines, but the Third Battle of Ypres delayed operations, after the Germans overran the group headquarters their location was lost. On 17 July 1955, a lightning strike set-off one of the remaining mines. There were no human casualties, but one cow was killed and some local property damage was sustained. The 21st cache was never found, and there are still several tonnes of high explosive buried somewhere under the Belgian countryside. A memorial to the Australian mining troops killed at Hill 60 during the course of the war was later placed at the site.

Battle of Vimy Ridge


In preparation for the Battle of Vimy Ridge between 9 and 12 April 1917, the British XVII Corps, commanded by Lieutenant-General Sir Julian Byng, relieved the French Tenth Army in the sector in February 1916, permitting the French to expand their operations at Verdun. The British soon discovered that German tunnelling companies had taken advantage of the relative calm on the surface to build an extensive network of tunnels and deep mines from which they could attack French positions. The Royal Engineers immediately deployed specialist tunnelling companies along the front to combat the German mining operations. In response to increased British mining, German artillery and trench mortar fire intensified in early May 1916. On 21 May 1916, after shelling both forward trenches and divisional artillery positions from no less than 80 out-of-sight batteries on the reverse slope of the ridge, German infantry attacked the British lines along a 2000 yd front in an effort to eject them from positions along the ridge. The Germans successfully captured several British-controlled tunnels and mine craters before halting their advance and consolidating their positions. The Germans grew uneasy about the proximity of the British positions to the top of the ridge, particularly after the increase in British tunnelling and counter-mining activities. Small counter-attacks by units of the 140th and 141st British Brigades, 47th (1/2nd London) Division, took place on 22 May, but did not manage to change the situation. The Canadian Corps relieved the British IV Corps stationed along the western slopes of Vimy Ridge in October 1916.

Other operations
Another example is recorded in Louis Trenker's Mountains on Fire. Whole mountain peaks in the Alps were exploded during the mountain war. Col di Lana, Lagazuoi and Marmolata, were a few examples.

End of mining operations
From Spring 1917 the whole war became more mobile, with grand offensives at the Battles of Arras, Messines and Passchendaele, there was no longer a place for a tactic that depended upon total immobility for its employment. As the tactics and counter-tactics required deeper and deeper tunnelling, (hence more time and requiring more stable front lines), offensive and defensive military mining largely ceased.

Underground work continued, with the tunnellers concentrating on deep dugouts for troop accommodation, safe from the larger shells being deployed.

According to the original trench maps, hospitals, mess rooms, chapels, kitchens, workshops, blacksmiths, as well as bedrooms where exhausted soldiers could rest, were hewn from the blue-clay and stone. Connected by corridors measuring 6 ft 6in high by 4 ft wide, they were fitted with water pumps which, when the troops left within weeks of the war ending, were slowly submerged. The developments at Hill 60 housed 3,000 men, those near Hooge 1,000. A brigade headquarters at the Vampire dugout near Zonnebeke, was captured and occupied by the Germans in their Spring Offensive in 1918, before being retaken in September. The level of activity can be gauged by the fact that during 1917 and 1918, more people lived underground in the Ypres area than reside in the town today.

Battle of Arras
In preparation for the Battle of Arras in 1917, the Royal Engineers had been working underground from October 1916, constructing tunnels for the troops. The Arras region is chalky and therefore easily excavated; under Arras itself there is a vast network of caverns (called the boves), which consist of underground quarries, galleries and sewage tunnels. The engineers devised a plan to add new tunnels to this network so that troops could arrive at the battlefield in secrecy and in safety. The scale of this undertaking was enormous: in one sector alone four Tunnel Companies (of 500 men each) worked around the clock in 18-hour shifts for two months.

The British attack plan was well developed, drawing on the lessons of the Somme and Verdun in the previous year. Rather than attacking on an extended front, the full weight of artillery fire would be concentrated on a relatively narrow stretch of 24 mi. The barrage was planned to last about a week at all points on the line, with a much longer and heavier bombardment at Vimy to weaken its strong defences. During the assault, the troops would advance in open formation, with units leapfrogging each other in order to allow them time to consolidate and regroup. Before the action could be undertaken, a great deal of preparation was required, much of it innovative.

To assist the attack, the Royal Engineers constructed 20 km of tunnels, graded as subways (foot traffic only); tramways (with rails for hand-drawn trollies for taking ammunition to the line and bringing casualties back); and railways (a light railway system). Just before the assault the tunnel system had grown big enough to conceal 24,000 men, with electric lighting provided by its own small powerhouse, as well as kitchens, latrines and a medical centre with a fully equipped operating theatre. The bulk of the work was done by New Zealanders, including Maori and Pacific Islanders from the New Zealand (Māori) Pioneer Battalion, and Bantams from the mining towns of Northern England.

Assault tunnels were also dug, stopping a few yards short of the German line, ready to be blown open by explosives on Zero-Day. In addition to this, conventional mines were dug under the front lines, ready to be blown immediately before the assault. Many were never detonated for fear that they would churn up the ground too much. In the meantime, German sappers were actively conducting their own underground operations, seeking out Allied tunnels to assault and counter-mine. Of the New Zealanders alone, 41 died and 151 were wounded as a result of German counter-mining.

Today, most of the tunnels and trenches are off-limits to the public for reasons of safety. A 250 metre portion of the Grange Subway at Vimy Ridge is open to the public from May to November and the Wellington tunnel was opened to the public as the Carrière Wellington museum in March 2008.

Second Battle of Passchendaele


In preparation for the Second Battle of Passchendaele, as early as the 17 October, assault units were given all available details about the German defences in their respective sectors, in order to facilitate early planning. Intelligence officers and artillery observers worked jointly in observation posts recording newly built German fortifications as well as those that had previously escaped notice, permitting the artillery to take necessary action before the offensive. To improve the logistical movement of artillery and supplies an extensive programme of road building was started. Ten field companies, seven tunnelling companies, four army troop companies and nine battalions were put to work repairing or extending existing plank roads. From the middle of October until the end of the offensive, a total of 2 mi of double plank road and more than 4000 yd of heavy tram line was constructed in the Canadian Corps area. Brigadier General Edward Morrison, commanding the artillery, also secured permission to use the roads to the rear for withdrawing disabled guns for repair.

Remains and memorial
Many of the largest craters have been left, often too large to fill-in, even today. The largest crater on the Western Front, the Lochnagar Crater, had been left for 50 years, but it had begun to be used by motorbikers and as a rubbish dump. Privately purchased in 1979, it is now a recognized 1914–1918 historic battlefield site.

The RE Grave Railway Wood Commonwealth War Graves Commission Cemetery was founded by Commonwealth troops in November 1915 and remained in use until August 1917. It commemorates the eight men of the 177th Tunnelling Company, Royal Engineers, and the four assistant infantrymen who were killed whilst tunnelling under the hill. Their bodies were left in situ, beneath the hill on which the memorial now stands.

Operations since WW I
Because World War II troop movements were too fluid, and tunnelling too slow, mining proved not to be worth the investment of effort.

Awards
Two members of the Tunnellers Companies were awarded the Victoria Cross:

Sapper William Hackett 254 Tunnelling Company, Royal Engineers awarded posthumously for helping his fellow miners when a tunnel collapsed at Givenchy-lès-la-Bassée, France on 26 June 1916. His medal is held by the Royal Engineers Museum and he is commemorated at the Tunnellers Memorial

Captain Coulson Norman Mitchell, of No 1 Tunnelling Company, 4th Canadian Engineers Royal Canadian Engineers for preventing the demolition of bridges on the Canal de I'Escaut, north-east of Cambrai on 8–9 October 1918. His medal is held by the Canadian Military Engineers Museum, CFB Gagetown, New Brunswick.