On 16 November the French D3 deep incline, underway since June, entered service and the French believed that they could take on the Germans. However, despite daily listening and a strong camouflet of 3.5 tonnes, the Germans responded with a charge ten times greater from the end of Kaiser Stollen on 10 December, forming a 70m crater and destroying four of the E shafts and much of the French front line and underground shelters. Fifty men were rescued but twenty-one were not found.

In September the Germans completed a gallery, Gotteberg, to protect the sector where the French had blown on 23 March. At the end of 1916, the Germans still had the advantage, gained through superior equipment, personnel and mortars, to systematically put shaft entrances out of action. Poor weather prevented aircraft observation, which would have alerted the French to the increase in spoil on the northern slope. The new German galleries were 10m beneath the deepest French workings and the French were unable to surprise the Germans. When they heard the French the Germans stopped work and used activity in the upper galleries to disguise the lower work. They could blow to a range of 30m without fear of retaliation from the French systems at 20 and 30m depth (see cross section). The French were forced to abandon the last seven shafts put into service, or to destroy them when blowing camouflets, owing to the short distance from the shafts to the ends of their galleries. Their radius of rupture was only 20 to 25m and caused very little damage to the German galleries. The French system of D shafts, intended to fight at 35ft depth, was barely in service before it was outclassed by the German galleries. The shafts were either abandoned or rendered unusable by German camouflets. To make matters worse the new X, Y and Z attack galleries passed beneath the French front lines at only 25, 20 and 30m instead of the planned 38m, owing to a levelling error by Captain Mathey.

At the end of 1916 the French began work on a series of new galleries, only one of which was started from the rear slope. This was a new deep gallery (V) on the eastern flank, driven on a steep gradient of 70 per cent and equipped with an electric winch and fan. In addition four major listening galleries were started from in, or near, the front line and a 22-tonne camouflet was to be blown from D1 to destroy a deep German gallery between D1 and D6. The camouflet was to be 11 tonnes gunpowder and 11 tonnes cheddite, but on 31 December, during charging, the powder went off and the blast killed thirty-six men at work in the gallery.

In January the French engineers were again relieved when there was a change of corps. Company 8/14 took over mines in the west, 8/64 in the centre and the mining company M5, afterwards M5/T, of which the commander had only moderate experience, in the east. In order to preserve some continuity Mathey remained in command. The French made efforts to regain the advantage and the driving of galleries took on an increasingly mechanized character to compensate for a permanent lack of labour. The Service Électromécanique operated generators, compressors, ventilators, pumps, winches, drills and borers, but electrical output remained inadequate. There was 1,800m of compressed air piping from the French rear position at the Mamelon Blanc feeding the pneumatic picks and pumps in the galleries. During the winter these were affected by freezing weather and rising water also flooded some of the galleries.

The V gallery in the extreme east was quickly begun, but only after the work was established was it found that the entrance was subject to flanking fire from the Bois de Cheppy, by which time it was too late to change the location. The lack of labour and delay in installing the 40cm railway hampered the removal of spoil. Work on the new listening galleries was hardly begun before one was halted by a German camouflet. Nevertheless the French planned new galleries, S and T, from their rear slope and began a ‘revenge gallery’ branched from X in reply to the German 35tonne mine of 10 December, creating a diversion by drilling from another branch. Despite a German camouflet on 5 February, the French were able to charge with 5.7 tonnes to destroy two German workings to the north-east and north-west.

On 24 February the Germans blew a mine in the mid-west of the ridge, destroying a French shaft, damaging two others and confirming French fears of major German deep workings. On 9 March, the French urgently considered a plan to lay three enormous mines to destroy the German galleries and surface positions and to give up the Vauquois position in favour of the Mamelon Blanc position. This involved placing three charges 60m apart, each of either 144 tonnes at 40m depth or 280 tonnes at 50m. This was not adopted, as it was estimated that the mines would only partly destroy the German surface and underground positions and the craters could then be used by the Germans as cover for maintaining their occupation of the ridge. To be effective the charges would have to be placed behind the northern lip of the craters which formed no man’s land, which was impossible to achieve, and if the French had that degree of freedom underground there would be no need for them to give up the ridge. On 9 March they decided to dig a fourth and final deep gallery, W, between X and V to reach 50m depth. The Germans blew a mine on 19 March, making a 60m crater and destroying two French shafts as well as the infantry and engineers’ shelters. It was to be the last of the large German mines. The French, however, were making some progress with their deep galleries. In February their X gallery came into service, in April Y, Z and T, and in June V and S. On 30 June the French blew what was to be their last mine to break surface, which destroyed a German machine-gun dugout. At these deep levels even massive charges no longer broke surface to form craters and mine warfare became an almost entirely underground affair. Its immediate purpose was no longer to attack surface positions, but purely to destroy the enemy galleries and kill the mining personnel. Using sensitive listening apparatus both sides tried to blow camouflets to cause maximum casualties to the miners of the opposing sides. When charges did not break surface or find enemy galleries there was frequently nowhere for the gas generated by the explosion to vent, in which case spherical voids were formed which the miners might then break into. In February the French discovered one 10m in diameter; the Germans used a 6m cavity as a listening chamber for several days before destroying it. By this time the Germans did not attempt to recover the bodies of their men killed by camouflets. Pioneer Tschörtner, posted to 1/Pi 30 at the beginning of 1917, explained the reasoning in an interview in 1970:

Pioneer Damman was buried by a French blow. We walled him up. We always did it that way because we no longer recovered people. Once we unearthed one. He had been surprised in a squatting position by a French blow not during the usual time for blows. The head sat in the right upper corner, the trunk was beneath and the legs were gone. We always closed the galleries after that.²¹

In the summer of 1917 the Germans worked on driving three new galleries deeper than any previously used. Rader Stollen in the east, Mittel II Stollen in the centre and Treppen Stollen to the west were to pass beneath the level of the sandstone gaize, through layers of clay and green sand, to reach limestone at over 100m depth. After driving horizontally into the hillside 42m beneath the level of the summit, they were steeply inclined to reach about 60m depth before doubling back and by March 1918 reached 95m.

In June 1917, the French decided to discontinue active mining on the west end of Vauquois ridge. The chief engineer of the 31st Corps recommended the adoption of a purely passive attitude, reacting only if the German miners became too threatening. The commander of the 64th Division, holding the line above ground, also approved a report by his commander of engineers to ‘put to sleep’ mine warfare in the whole Vauquois sector. From that date the French proposed to carry out only maintenance work and monitoring. There remained the problem of German threats. If the French were to blow a German gallery approaching their workings it would reawaken mine warfare, which the French could not then counter, as their system was insufficiently developed and had been allowed to flood. It thus proved extremely difficult for the French to disengage from mine warfare at Vauquois. Their attack galleries were within a few metres of the German lines and were inevitably met by German miners. On 26 June a German borer broke into the head of the French T gallery. The French constructed a barricade and brought in dynamite, but the Germans blew as they were doing this, burying a corporal and wounding, gassing and concussing an officer. The French attempted to continue laying a charge but the Germans blew again, killing a corporal and a sapper, and then blew a third time the following day.