Easter Monday 1917 was also the start of the Battle of Arras, instigated by the British. The battle frontage extended southward from Lens, the city just south of Loos where the 3rd ATC was in action. By the end of the battle, the German front line had been pushed eastward by as much as 50 km. It so happened that the hinge point between the pre-battle British front line and the post-battle front line, lay directly over number 1 shaft in the 3rd ATC’s mine gallery at Loos. While the company was not required to use its tunnelling skills for the battle, its men were involved in carrying ammunition to front line British units and repairing roads across the old no man’s land. One road, leading into the village of Levien is named “Australian Road” on official British trench maps of the time, in recognition of the work of the 3rd ATC during the battle.
On 28 June 1917 three parties of tunnellers accompanied a large raiding party. Their task was to locate and destroy German mine shafts and dugouts. Their Commanding Officer, Major L. J. Coulter, had returned from leave only an hour before and insisted on accompanying them and just before the tunnellers were to return to their lines, Major Coulter and his batman were shot and killed by a sniper. Command of the 3rd ATC was then assumed by Capt. Alex Sanderson for the remainder of the war.

Two weeks after this the German miners at Hill 70, blew the last of their mines of the war along the British sector of the front. The resulting crater was named Coulter Crater in honour of their widely respected deceased Australian tunnelling officer. In response the Australian tunnellers went on the offensive and within days had broken into the German mining system, capturing 234 m of opposing galleries. Finally, on 27 July 1917, the Australian tunnellers blew their last and one of their biggest camouflets of the war, a 10,000 lb “maximum” camouflet. By that time the German mining threat had all but evaporated and the 3rd ATC, like its two sister companies, embarked on a new role. Two weeks after blowing its last camouflet at Hill 70, the Canadian Corps captured the hill and pushed back the German lines down the eastern slope of the hill. Two detachment of tunnellers accompanied the Canadian infantry, identifying and checking captured dugouts and posts. Work on that occasion resulted in the 3rd ATC being awarded two Military Crosses and a Military Medal.

Through the autumn of 1917, the all Australian tunnelling companies were mostly engaged in dugout construction works. At Loos, following the capture of Hill 70, the 3rd ATC’s operational front was extended northwards to cover the extensive, interconnected tunnel complexes opposite the villages of Hulluch and Cite St. Elie on the southern bank of the Hohenzollern Redoubt (this was a strong German defence system near Loos). Here the company embarked on an extended period of dugout construction and maintenance in the tunnels in the sector.

In November 1917 the 3rd ATC settled down in Loos and during the winter the 3rd ATC started one of its largest projects, the construction of a tunnel, what later became known as the Hythe Tunnel, connecting its old front line mine gallery system with the new front line trenches lying on the eastern slopes of Hill 70. Infantry moving along Hythe Alley, the main communication trench that passed over Hill 70 to the front, were exposed to German observation. A subway below the hill was therefore proposed and work commenced in January 1918.
A German spring offensive soon followed and on 9 April 1918 a second thrust was made by the Germans against the allied line near Fromelles. At the time a detachment of 38 men from the 3rd ATC was constructing machine-gun positions around Armentieres. Such was the seriousness of the situation and the ensuing confusion that followed that the detachment was placed in the front line to act as infantry alongside some elements of a British unit outside Erquinghem-sur-Lys. During the following five days the unit fell back through Armentieres (north-west of Lille) to Strazeele and at times was taking rear-guard positions attached to the 12th Battalion, Suffolk Regiment. The exhausted tunnellers were then transferred to the 1st Australian Division’s engineers and once there, contact with the 3rd ATC headquarters was re-established. Lorries were despatched from there and the men returned to their own unit’s Headquarters. (It is not possible at this stage to discover the names of those who were part of this detachment).
By April 1918 the 3rd ATC suffered the effects of the German attack on the Lys front when the area from the La Basse Canal to Vermelles was subjected to days of unrelenting gas shelling. Over the three days commencing 8 April, the 3rd ATC suffered 43 cases of gas shell poisoning from the two section working near Vermelles. Fortunately no cases were fatal.