In the meantime, in March 1916 the British used mines in two operations involving infantry attacks at Hohenzollern Redoubt and St Eloi. At the end of the Battle of Loos on 13 October 1915 the British had attacked a complex of German trenches known as the Hohenzollern Redoubt and occupied half of the position. With the opposing lines very close to one another, tunnelling was carried out through a clay layer which was about 20ft deep. Below the clay was chalk of increasing hardness. Norton Griffiths suggested on 24 October that Preedy’s 170 Company be moved so as to be opposite this position and that ‘a big offensive work’ should be carried out over the winter by two tunnelling companies using compressors to power drills to make bores for blasting.⁵ Preedy’s Company began work for a mining attack on the Hohenzollern Redoubt on 14 December 1915. By the end of the month he was in the process of sinking six shafts, with two sections of 180 Tunnelling Company due to be attached to his unit to begin another three. Preedy carried out mining in the clay to distract the Germans from their drilling into the chalk and the mine fighting during the winter resulted in a number of craters with high lips. The Germans were repeatedly more successful in occupying craters very quickly after they were blown, even when the British blew them. The reasons for this lay in the superior overall level of training of the Germans, especially the ability of NCOs to show initiative and leadership, combined with superiority in mortars, grenades and night illumination. The Germans used the advantageous observation afforded by these new craters to capture the British front line, a trench known as the Chord. By late February 1916, however, 170 Company had driven three galleries through the chalk between 161 and 200ft to within 30ft of the German front-line trench in the Chord. The galleries were charged on 29 February: the largest, 10,055lbs (Crater B), was at 30ft depth, the others, both 7,000lbs (Craters A and C), were probably at a similar depth. An additional mine of 1,000lbs, beneath the lip of crater No.2, was designed to throw debris into a network of German saps.⁶ The decision to use these mines was taken only ‘after much discussion’ by the I Corps commander, General Gough.⁷ Blowing the mines would lead to a fierce fight and the Germans might end up in possession of the new large craters and in a yet stronger position. Delay, however, would lead to the discovery of the charges by the Germans and Gough decided that an attack to retake the Chord should go ahead by two battalions, the 8th and 9th Royal Fusiliers, on 2 March. The attack orders prepared by 36th Brigade were extremely detailed and embodied a great deal of experience from the crater fighting of the previous months. In particular, the actual firing of the mines was used as the signal for both the infantry attack and the opening of the artillery: there was to be no preliminary bombardment. This acknowledged the central role of the mines. There was a desire to use surprise and rapidity rather than the step-by-step procedures of a siege, and a determination to beat the Germans in the race to take the beneficial position afforded by mine craters. There was no time interval between the firing of the mines and zero hour, when the troops were to leave their trenches to cross no man’s land, but troops were warned to avoid falling debris:

The assault must be delivered immediately the danger of injury from the falling earth is over, and before the dust and smoke have cleared away. Everything depends on taking the enemy by surprise.⁸

It was hoped that the German wire in front of the 9th Royal Fusiliers’ attack, which was known to be formidable, would in the south be buried by debris from Crater A. The attackers were warned not to enter the bottom of the crater for ten minutes owing to the danger of gas, or 15 minutes if there was no wind. Trench mortars were to fire smoke bombs to screen the southern flank, with orders that it was ‘essential that these bombs should be fired while the debris from the mine is still in the air.’⁹ To gain entry and exit from the craters, which would have steep and unstable sides, the attackers were equipped with 15ft ladders, and as part of consolidation pathways were immediately to be cut.

The three main mines formed craters with diameters between 100 and 130ft and thus destroyed large portions of the Chord. The infantry at once assaulted and in the south, between and around the new Crater A and the enlarged Crater No.2, the 9th Royal Fusiliers reached the German trenches with hardly any casualties, as the Germans were still emerging from their dugouts, and took 80 prisoners. To the north, however, the 8th Royal Fusiliers, between and around craters B and C, were not so successful. The Germans were manning the parapet as the attackers attempted to cross no man’s land and shot down all except a few on the right. In the following days, the Germans captured a crater (Triangle Crater) on the southern end of the Chord and made strenuous efforts to take Crater A. The 36th Brigade had to be relieved by the 37th. On 18 March, the Germans blew five shallow mines laid short of the British line in a counterattack; the Bavarian attackers were immediately behind the mines as they blew and, although this caused the attackers alarm, they were able to force the British back to their old front line. The British held only the near lips of the craters; the forward lip closest to the Germans proved impossible to defend ‘as its breadth, and the great masses of clay, twelve to twenty feet high, lying about, prevented a field of fire being obtained.’¹⁰ Attempts by the British to hold the interior of the craters also proved too costly in men. The Germans poured artillery and mortar projectiles into the crater and the bottom became a morass of liquid chalk and black mud, while the crumbling sides were too unstable to consolidate. The Germans occupied their side of the lips and the British abandoned further attempts to hold the Chord. The commander of the 37th Brigade, Brigadier General Cator, reported that trying to make the far lip of the crater the front line was not practicable and that the best options were either a trench line in front of the crater or the lip nearest the British lines. At Hohenzollern both sides held the near lips, leaving the interiors of the craters unoccupied, which they filled with barbed wire and iron chevaux de frise. The resulting line of craters along no man’s land, with each side occupying the opposing lips of the same crater, was the characteristic surface form of an active mining sector on the Western Front.

The Hohenzollern Redoubt attack showed that even with the advantage of destroying the German front line by surprise mining attack, the British could not always capture and hold the ground gained. They might not win the race across no man’s land before the defenders were alerted to the attack. It also demonstrated that holding a crater against concentrated fire and determined German counterattack was extremely difficult. The question of the right time to fire mines, and the perceived danger of falling debris, was to recur during 1916.

While the Hohenzollern fighting was still in progress, the British 2nd Army was planning another larger attack with mines at St Eloi. These mines were to come as a profound shock to the Germans, and for the first time they really realized the nature of the British achievement in forming their Tunnelling Companies. But the attack was to prove again that the British lacked the operational art to exploit the potential of mining.

In the autumn of 1915, Hickling and the sappers of 172 Company managed to sink shafts through the sandy clay, called Paniselien or ‘bastard’ clay, to the dry Ypresian or blue clay below. These shafts were to offer the potential of a mining attack combined with infantry, which had not been available when they had blown their mines at St Eloi in July 1915. The shafts had to be strong enough to hold back a very heavy pressure of water and wet sand. At 23ft they were into the bastard clay and at 43ft they reached the blue clay.¹¹ It was wettest at the junction between the bastard and the blue clay. Working with Hickling was Lieutenant Frederick Mulqueen, who took over when Hickling was promoted in early in 1916. He recalled that they placed a pumping station just below the start of the blue clay and continued down to about 64ft. The first deep gallery through the blue clay, D1, was towards the Mound. Miners preferred the tunnels to the trenches and Mulqueen recalled fondly that the blue clay layer was a refuge from both the pervading shelling and the sodden conditions of St Eloi: