The Germans pushed the first of their deep systems in front of their lines at the beginning of 1917 during the wettest season. However, in the very wet spring of 1917, the Germans decided to pull back from Petit Bois, Hollandscheshuur and Bois Quarante, as British shelling had rendered the positions untenable and used heavy blows to destroy, they hoped, the British mine workings. They had already begun to prepare new defensive shafts further back. Noises were seldom heard from the British and Füsslein concluded, retrospectively, that they had laid their charges and were just carrying out maintenance on their galleries. Only later did he realize the extent to which the British had placed mines and protected them against wet. When the Germans blew against the galleries containing the charges the British could often repair the breaks to the firing circuits and if necessary place another charge adjacent to detonate it. On Christmas Day 1916, Füsslein reported that in only two places had deep British tunnels been detected, although in others it was suspected. However, British deep mining activity indicated that they were preparing a mining attack and this could only be intended to accompany an attack above ground. He had insufficient men to carry out defence work at the upper levels and also to drive new tunnels at the deep level and asked for four more mining companies, of which three were provided to him in January 1917.⁴²

At the beginning of February 1917 Füsslein drew up an instructional leaflet to commands and divisions for distribution to the infantry. In it he pointed out that the British were likely to precede an attack with numerous mine explosions in front of and in the German front line. Therefore the front trenches should be held thinly to minimize the effects and they should treat the mine blows as the prelude to an attack. Füsslein stated after the attack that at the end of February the signs of a British attack became more clear. However, on 8 March he reported that, as a result of several defensive blows, a full tunnelling attack on the Wytschaete salient was no longer possible. On 15th he reported that the situation was unchanged and that all areas were either safeguarded or no deep mining had been detected. On 28 April, however, Füsslein reported that the silence of the British underground, combined with the digging of jumping-off trenches in several places, pointed to the likelihood of a major attack.⁴³ Füsslein claimed that in March or April General Ludendorff gave the XIX Corps authority to withdraw from the forward positions in the Wytschaete salient if there was a danger that they could not be held. This option, Füsslein says, was rejected by the corps commander. The evacuation of the Wytschaete ridge was considered at a conference of Army and corps commanders convened by the Army Group Commander, Crown Prince Rupprecht. None of the corps commanders considered the evacuation necessary and according to the German Official History, the situation below ground was not mentioned, so far as is indicated by the notes and reports of the conference. On 10 May Füsslein reported that, although the British were working at the deep levels in all sectors, his efforts to oppose them had been successful and they were only doing so where they hoped to pass unnoticed. He went on to admit, however, that a British attack in great depth was still to be expected at those points where he had not been able to counter the British mining. These were at the Caterpillar, Hill 60, the Bluff, between the Bluff and St Eloi, Spanbroekmolen and Kruistraat, and he repeated his warning: ‘If a great British attack takes place it will be preceded by large blows at some of these places in front of or in our front line.’⁴⁴

On 24 May Füsslein reported signs of underground work in these areas, but Spanbroekmolen, where the British gallery was blown by a German mine, was no longer considered immediately threatened. Füsslein believed that the danger of a British mine attack against the Wytschaete ridge had been averted by German countermeasures. However, he was convinced that his defences underground were not secure everywhere and that at many places deep blows were not only possible but very probable as a prelude to a major British attack. After the battle, the commander of XIX Corps, General von Laffert, stated that apart from some places, the miners were of the opinion that no sort of danger existed. If there had been any doubt the natural consequence would have been the early evacuation of the whole forward position. He claimed to have left only small garrisons in the forward lines of the places still thought to be threatened, but there is no indication of this in the German regimental histories. The 4th Army reports made no reference to mining after 12 May.⁴⁵

Although the Germans achieved some successes in halting the British mining offensive, it was geological conditions which were the most powerful limiting factor. Far fewer than the projected number of mines were actually ready or used in the attack. On 16 April Harvey reported that of twenty-nine mines, eighteen were ready for use, and another three or possibly four would be ready by 15 May. For three mines the gallery had been destroyed, for two their completion or recovery was doubtful and the remaining two had been abandoned and were ‘not required’.⁴⁶ In addition, the four mines charged for the June 1916 attack on the far south of the front at the Birdcage were not in the area of Plumer’s new attack. He decided to keep these in readiness for use, but they were not required on 7 June.⁴⁷

As the month of June approached, the British artillery fire became steadily heavier. Communications to the front line became more difficult, hampering the work of the German miners and breaking power cables from generating stations. Füsslein ordered his miners to blow their systems, even if it meant destroying them, if there was a possibility of destroying British mines. However, the Germans could not then interfere with the British work to recover their charges as they had destroyed their own shafts and galleries. They buried their own shaft entrances so that the attackers would not find them. German intelligence suggested that the attack would take place on 10 June. On the British side, doubts arose on the eve of battle that the mines would detonate, having been in place for so long and subject to disruption from enemy action and the wet. Haig’s concern was made known by the Chief of the General Staff on 24 May:

There appear to be many instances in the IX and X Corps of a disbelief as to whether the mines can be effectively exploded. This should be rectified. Expert miners and electricians have tested the mines and expressed their satisfaction with the arrangements.⁴⁸

Just over a week before the battle was to begin the possibility arose, however, of all the mines being rendered useless. At the end of May the British obtained a German document giving clear information about new German defensive tactics, which appeared to jeopardize the whole Messines mining attack. In the event of a British attack, the Germans appeared likely to adopt the tactic of abandoning their front line and placing a heavy artillery barrage there, as well as on no man’s land and the British front line. The pressing need for the British was to force the Germans to disclose the locations of as many of their carefully concealed gun batteries as possible so that British artillery could destroy them before the attack was launched. The British Chief of Staff, General Kiggell, wrote to Plumer on 29 May in the light of this information. He informed him that Haig wished him to meet the following day so that the decision could be taken as to whether to explode the mines prematurely, before the Germans had withdrawn and as a means of fooling them into believing that the attack was being launched and thus bringing their guns into action and revealing their location. Haig wished to discuss whether the mines should be blown before the attack, i.e. on ‘W’ day, four days before, followed by immediately seizing the craters with patrols and plenty of Lewis guns, but keeping the mass of troops back. The reports that Plumer had indicated that in places the Germans were holding their front line in strength, in others by posts only, but there was no definite evidence of anything in the nature of a general withdrawal from the front line. His response at first was to use the mines prior to zero day and to endeavour to occupy the German front line. He summoned his corps commanders and found two in favour, one not. He told them to consult their divisional commanders and report to him the next morning. After this none favoured the prior occupation of the front line and all thought that the original plan should be adhered to. At the meeting with Haig, Plumer proposed to deal with the situation by bringing forward his destruction fire by two days and devoting the last two days before the attack entirely to counter-battery fire. Haig concurred with and supported this decision and the use of premature blowing of the mines was ruled out as a means of forcing the Germans to disclose their artillery batteries.⁴⁹

The Messines mines were placed directly beneath the positions that the British wished to destroy. In contrast to the Somme in 1916, where the extreme difficulty of working quietly in chalk meant that it was all but impossible to get beneath German positions, so the mines were often halted in no man’s land and relied on shock and the fougasse effect of throwing debris over the position, at Messines the ability to work deeply and silently through the clay level gave the British the ability to position mines exactly for maximum effect. The time of the blowing of the mines was now accepted as being on zero. At Kruistraat, where Hudspeth had laid three mines each beyond the other, he attempted unsuccessfully to persuade the commander of the 36th Division, General Nugent, that he should blow the farthest mine later to catch the Germans as they fled:

The mines were so laid and the firing arrangements so made that the second line mine could be blown at a time interval after the first mine, of a few seconds, by putting in a time fuse between the two wires.…This had never been done before. The General in charge of the Infantry was too worried about it, the possibility of the second mine not going off at the right time or being too long delayed, to catch our own infantry he wouldn’t risk it, even though I showed him at the camp exactly how it could be done. I gave a demonstration with actual explosives but Nugent wouldn’t have it and so they all went up together.⁵⁰

Harvey and Stevenson drew up orders for the safety of the British infantry:

Prior to the firing of the mines it was necessary to frame such instructions to the assaulting troops as would obviate casualties resulting from the effect of the enormous concentration of high explosive at the depth of 70-100 feet below the surface. There was no information to be obtained from history as no military mining had ever dealt with so many large charges from one operation.⁵¹

No man was to be within 200yds of a charge until twenty seconds after it had been blown. All trench and surface dugouts within 300yds of a charge were to be evacuated and men were to be clear of any trenches or structures which might collapse when the mines blew. All tunnelled dugouts and subways were to be cleared within 400yds. Old brick buildings were to be avoided. The assaulting troops were not to enter the bottoms of the craters owing to the danger of explosive gas.

Nine Divisions made the initial assault. It is often said that the British Prime Minister, Lloyd George, heard the detonation of the mines in 10 Downing Street. In fact it was the opening salvo of the synchronized artillery which was heard as the British artillery was timed to open fire simultaneously with the blowing of the mines.⁵² At Hill 60 an artillery officer witnessed the mines under the Hill and the Caterpillar:

At exactly 3.10 a.m. Armageddon began. The timing of all batteries in the area was so wonderful, and to a second every gun roared in one awful salvo. At the same moment the two greatest mines in history were blown up - Hill 60 and one immediately to the south of it. I cleared everyone out of the dugouts and was watching for it. Never could I have imagined such a sight. First, there was a double shock that shook the earth here 15,000 yards away like a gigantic earthquake. I was nearly flung off my feet. Then an immense wall of fire that seemed to go half-way up to heaven. The whole country was lit with a red light like in a photographic dark-room. At the same moment all the guns spoke and the battle began on this part of the line. The noise surpasses even the Somme; it is terrific, magnificent, overwhelming. It makes one almost drunk with exhilaration, and one simply does not care that we are under all the concentrated fire of all the Hun batteries.⁵³

The history of the German 204th Division described the Hill 60 blows in these terms:

The ground trembled as in a natural earthquake, heavy concrete shelters rocked, a hurricane of hot air from the explosion swept back for many kilometres, dropping fragments of wood, iron and earth, and gigantic black clouds of smoke and dust spread over the country. The effect on the troops was overpowering and crushing…the trenches were now the graves of our infantry.⁵⁴

The mine at the Caterpillar, placed behind the German front line, slammed the trench shut and buried the garrison alive. The 204th Division claimed to have lost 10 officers and 677 men killed by the explosions at Hill 60 and the Caterpillar. However, German reports and histories tended to ascribe their defeat and losses almost entirely to the mines, whereas the artillery and infantry attack had a devastating impact.⁵⁵ Füsslein dismissed these reports, claiming that he could prove that at most thirty-five were lost from a single blow and that the remainder were lost in the ensuing fighting. At St Eloi British infantry converged around the salient, as they had attempted on 27 March 1916. The new mine crater was 50ft deep and 270ft in diameter and made the existing craters appear like shell holes. As before, the broken ground made progress very difficult, but they met little opposition from defenders.⁵⁶ At Petit Bois the two mines caused a wide obstruction for the attackers, but also destroyed the German opposition. Lieutenant Wallace Lyon, of the 7th Leinster Regiment, faced:

…the possibility that we might be blown sky high in the event of any delay of the mine explosion…the orders were to go on the first shoot of the artillery barrage whether the mine went up or not... But soon we were confronted by a vast crater full of smoke and gas which extended the complete length of our front, so without loss of time I took half the Company round one side and [Lieutenant] Hamilton the remainder round the other flank… We found [the Germans] with few exceptions well shaken with the explosion and we bombed all the dugouts beyond the crater. Although we must have collected and sent back between two and three hundred prisoners, the whole operation as far as I was concerned was a cakewalk.⁵⁷

Press and VIPs were assembled on specially built platforms on Kemmel Hill and from here Lieutenant Brian Frayling observed the detonation of Spanbroekmolen two miles away: ‘…a white incandescent light darting high in the air. We had calculated the enemy here would go up as gas at over 3,000 degrees Centigrade.’⁵⁸ This mine was fifteen seconds late, but the infantry did not wait before advancing and some men of the 14th Royal Irish Rifles were already in no man’s land when they were thrown off their feet by the blow:

But there were no casualties, and the men quickly closed in to the barrage. The size of the craters to be skirted and the darkness made the keeping of direction a matter of difficulty. It would have been impossible but for the use of compasses by the platoon commanders. (Captain Cyril Falls)⁵⁹

Frayling visited the site after the ridge was taken: ‘It left a deep crater and the largest piece of the enemy I could locate there in daylight was a foot in a boot.’⁶⁰

Plumer’s Chief of Staff, General Harington, also went over the ridge the day after the attack:

I shall never forget the sight. I remember well going into a concrete dug-out near Spanbroekmolen…and finding four German Officers sitting round a table – all dead – killed by shock. They might have been playing bridge. It was an uncanny sight – not a mark on any of them. I can see their ghastly white faces as I write. In the wallet of one of them was found a copy of a message sent at 2.40a.m. – 30 minutes before zero – saying ‘Situation comparatively quiet.’⁶¹

The mine at Ontario Farm, placed beneath 90ft of running sand, threw up hardly any lips and for a long time after the blow gas from the explosion continued to rise to the surface: ‘…the crater resembled a seething cauldron, the semi-liquid mud bubbling like some gigantic porridge pot on the boil.’⁶²

The explosion was understood to have caught two battalions of the 17th Bavarian Infantry Regiment during a relief, half of which were ‘as good as annihilated.’⁶³

The Ontario Farm, Trench 127 and Trench 122 (Factory Farm) mines were on the front of the II Anzac Corps. The splitting of the advance, and the difficulties of visibility, added to those caused by the barrage, caused some Australian commanders to question whether ‘the difficulties created by the mines outweighed the advantages.’⁶⁴ Where there was no mine at the Petit Douve salient, New Zealand troops still captured the German front line trench. On the southern flank of the attack, the Factory Farm crater lay just outside the attack area and 150yds within German territory, but Australian snipers succeeded in keeping the Germans from occupying it.

Harvey reflected the reservations held by infantry commanders in an evenhanded assessment of the value of the Messines mines. He pointed out that many of the objectives had been chosen fifteen months before June 1917 and many were completed for the postponed 1916 offensive:

The mines of an offensive system after being charged cannot be moved to suit altered surface conditions. They must be abandoned or fired for moral effect. In this case the moral effect is undoubted and is confirmed from many enemy sources.⁶⁵

In the intervening period between the idea of the ridge first being mined in 1915 and June 1917 the British had acquired the technology and skill to capture such a powerful defensive position from the Germans. Harvey acknowledged that, by 1917, mining was being overtaken by other fighting methods:

Some consider that the destruction of enemy personnel and damage to his morale was worth the effort, while others, admitting the moral effect, consider that the objectives had not been selected with due regard to the tactical situation above ground, and that the casualties inflicted on the enemy, as he was holding his organization so lightly were not in proportion to the amount of labour and material expended in the construction of the mines. Most commanders think that with the introduction of gas, aeroplanes, tanks and all the other innovations of modern warfare, mining only adds a further complication to the operations without corresponding benefit.⁶⁶

Messines was a limited objective battle and mining assisted with the first stage. Mines were particularly suited to dealing with concrete bunkers, which were hurled upside down by the explosions. The succeeding phases of the battle, however, relied on artillery and infantry and it is possible that the British could have taken the ridge without the mines. In combination the Germans were clearly unable to withstand the attack. Füsslein claimed unconvincingly that the German 2nd Division, by following the measures in his leaflet, held their ground better than the others, which could have withstood the mining attack had they done the same.

Whilst on the Messines–Wytschaete ridge, the Germans failed to anticipate the scale of the British mining offensive. To the north in the Ypres Salient they overestimated British intentions, both before and after the Battle of Messines. The British dug tunnels at the Yser canal north of Ypres to conceal bridging equipment for the coming attack, which were taken by the Germans to be offensive mining. The Germans formed two new mining companies, which set about sinking defensive systems at Boezinghe and Het Sas, both in their front line, to 10–25m depth and from 100–300m behind, which they managed to sink to 30–40m. At both locations they ran tunnels with great difficulty under the canal, but they found no evidence of British mining as there was none taking place. At Railway Wood, just north of the Menin Road at Hooge, where the British 177 Tunnelling Company had been since late 1915, the fight became intense and the Germans brought in another Company alongside 352 Pioneer Mining Company. Füsslein believed that they forestalled the British at Railway Wood after the Battle of Messines with a series of mines blown in their own lines on 13 and 14 June 1917. The British had never planned a mining attack there and the German blows were nowhere near their galleries. This contradicts Füsslein’s claim that, after Messines, he resisted attempts to panic blow their systems in the Ypres Salient and was backed by the Army commander. He implied that the British did not begin the Third Battle of Ypres with mine blows because their tunnellers could not get close enough. In fact the British had not prepared mining attacks and the German efforts had been misplaced.⁶⁷

Füsslein stated that the judgement of the German 4th Army and Headquarters vindicated the miners, and summed up his account of the Battle of Messines by blaming ignorance of mine warfare amongst infantry commanders:

It was astounding, after all the experience of mine warfare in Flanders, La Bassée, Champagne and the Argonne, the disregard and lack of awareness of this ancient and yet modern weapon. This ignorance came to light everywhere, where lack of historical knowledge, expertise and experience was combined with arrogance. Divisional commanders rejected mine warfare because they did not understand it; others made it the scapegoat, although they knew secretly that they had insufficiently valued this weapon. The miner in Flanders stands nevertheless upright and proudly there in the knowledge of having done his duty, recognized only by the few who know of his deeds.⁶⁸

For the Commander of Miners of the German 4th Army, the battle was also a personal tragedy. On 7 June 1917, with the words: ‘A Prussian Ensign does not surrender’, his son, eighteen-year-old Hans Georg Füsslein, serving with the 25th Pioneers, died defending the village of Messines.⁶⁹

Messines was the greatest and last mining attack of the war. Afterwards, the scale of mining reduced on the British as it had on the French fronts, although the British desire for dominance prolonged it in their sectors. The number of mine blows, 117 British and 106 German, was reduced in 1917 by six-sevenths compared to 1916, owing mainly to the Germans withdrawing or being driven from the active mining fronts.⁷⁰ On the remaining mining front, at Givenchy-lez-la-Bassée–Loos, the opposing systems were so well developed that further progress by either side was virtually impossible.