…effort dissipated in countless shallow and wet galleries in the front line, paltry beginnings of deep tunnelling, again in the front line, with little imminent prospect of getting deep. Therefore defence against deep attack was nowhere possible.²¹

The 352 Pioneer Mining Company under Lieutenant Schmölling at Railway Wood, the Experimental Pioneer Company at Hooge and Hill 60, and the 1st Reserve Company of Füsslein’s 24th Pioneers at the Bluff all struggled. The shafts, sunk with tremendous difficulty, which were stopped at 20m should have gone deeper to get to the dry clay. Instead they were ‘just glorified sumps’²² and they were blowing their charges in the level of the waterlogged strata. In the autumn of 1916 the Germans were unable to advance galleries much distance from these shafts and so each time they blew they damaged their own laboriously sunk shafts. Tactical control of mining remaining with divisions, however, made it difficult to change the practice of shallow mining from the front line. Moreover, the shallow levels had to be kept for defensive purposes, but they had insufficient manpower to push forward new deep workings while maintaining the old shallow systems. In reality the old systems were becoming ‘pure death traps’, partly because the single shafts had only one exit and partly because British artillery and trench mortar bombs were far more effective at destroying shallow mine galleries. This induced the infantry to agree to give them up. It was also difficult for the miners to give up their existing shafts: ‘It was a constant struggle with the traditional ways until the new mine warfare tactics established themselves.’²³

The new deep levels, begun in June 1916, were sunk 100 to 300m behind the German front and were gradually extended along the whole line. There were delays caused in particular by a shortage of manpower and, of four new companies which Füsslein requested, only two were granted: ‘The enemy meanwhile continued working quietly and steadily. The English, being tough and energetic, only blew when we threatened to get extremely close to them.’²⁴

The lack of deep systems prevented the Germans from detecting the advance of the British galleries, but from aerial photographs, and the frequent accumulations of bluish grey sandbags, Füsslein concluded that on the whole of the Wytschaete salient and further north the British were working in the clay level.

Füsslein complained of difficulties with supplies to maintain the larger and deeper shafts, of a shortage of miners, of increased British shelling of shafts causing the death of valuable miners, and also of the unwillingness of the infantry to help and materials being thrown away. Füsslein tried to increase awareness of the miners’ work through conferences and lectures, but frequently was told that miners were to be kept away as their presence only caused the British to mine. Often he encountered the belief that his miners should prevent every enemy blow, which he likened to expecting the artillery to stop every enemy shell. The divisional commanders could not accept that the British had gained a year’s head start over the German miners: ‘...amongst our troops there was a general lack not just of understanding but also of a desire to understand.’²⁵

The opening of the Battle of Messines on 7 June 1917 saw the largest mining attack in the history of warfare. It was the largest quantity of explosives deliberately detonated at one time and the most effective integration of mines with an attack. The history of the British mining operations and the German attempts to defeat them shows that many more than the nineteen mines blown were planned and laid. Many of the mines were laid in mid-1916 and had to be defended against German attack and protected against deterioration. In some cases this was for more than a year. Other mines, by contrast, were ready only days or hours before the attack began. Northernmost were two mines at Hill 60, where in the spring of 1916 the 3rd Canadian Company had relieved 175 Tunnelling Company. The Canadians took over the ‘Berlin tunnel’, which was in the Paniselien or ‘bastard’ clay at 90ft, and drove a branch beneath the hill, which in three months had passed under the German mining system before running into bad ground. As it was close enough to destroy the German front line they began a charge chamber, but as they enlarged the gallery it caved in with an inrush of sand and water with yellow clay, indicating that they were almost out of the clay bed. The leak was sealed and a series of small chambers had to be prepared to take a charge, into which they loaded 53,500lbs of ammonal, with an additional 7,800lbs of priming slabs of guncotton packed into the spaces. They completed this on 1 August 1916. The Canadians then dug an intermediate level system at 50ft to form a protective screen above their deep tunnels. They also drove towards the German-held Caterpillar, the spoil heap north of the railway line opposite Hill 60, and again ran into bad ground. They plugged the gallery, side-stepped to the right and descended 15ft into the clay. The gallery was continued to under the German second line and a charge chamber completed by 20 September. While they were loading the explosives, however, gas and water from a captured German gallery flooded the whole of the Berlin tunnel and cut off the charge. When they eventually regained access they discovered that the secure waterproofing meant that the charge was undamaged. Three independent sets of firing leads were installed, allowing nine circuits and sixty detonators. The charge was 70,000lbs. To improve access to the Berlin tunnel the Canadians began to sink a shaft to form a watertight entry past the running sand layer, which would enable a more effective seal than the inclined entrance from the railway cutting. At the beginning of November the 1st Australian Tunnelling Company relieved the 3rd Canadian Company and continued this shaft to 94ft to connect with the Berlin tunnel. They constructed a deeper level defensive gallery to further protect the mines, which were to be kept ready to fire when the offensive was rescheduled. There were clear signs that the Germans were sinking a shaft almost directly above the Caterpillar mine and the Australians blew a camouflet from a branch gallery, causing smoke to rise from two points in the German lines, but also damaging the leads to the charge. The Germans then fired a charge which broke the leads of the Hill 60 mine and cut off miners for two days. Aggressive underground fighting to defend the charges would have alerted the Germans to their presence, so the tactic used by the Australians was to engage the Germans from their upper level galleries to keep them occupied and to hide any sounds from the deep galleries. The Germans carried out a surface raid, which the miners took part in, and thirteen British mine shafts were located and destroyed. The entrances to the deep British systems, however, were beyond the reach of the raiders and Füsslein himself reported that although they had detected the British system at 20m there was no guarantee that they were not also deeper. He later claimed that he realized that the shallow level work was being used to disguise the deep work.²⁶