North of this dividing line were three very serious obstacles, namely, Auchy itself defended by impassable wire entanglements; a work of large area and enormous strength known as the Hohenzollern Redoubt; and a group of Quarries close to the Lens-Hulluch Road.
The 9th and 7th Divisions had met with great initial success on the 25th September 1915, the former overrunning the Hohenzollern Redoubt and gaining a position beyond it on a large slag-heap known as Fosse 8, while elements of the 7th Division sweeping the enemy's defence of the Quarries before them had gained the outskirts of Cité St Elie and Hulluch beyond the Lens-Hulluch Road. The unfortunate check to the advance of the 2nd Division at Auchy, however, had exposed the left flank of the 9th Division, who were afterwards ejected from Fosse 8, while the 7th on their right had been unable to retain their advanced positions across the main road.
Desperate fighting ensued for the possession of these strongholds until the conclusion of the battle about 13th October. At that date the Germans retained possession of the whole of the Quarries and the greater part of the Hohenzollern Redoubt. Between the two the British had driven a wedge so that the part of the Hohenzollern which remained in the enemy's hands formed an abrupt salient, of which the west face was formed by a trench irreverently named by the British "Little Willie," and the south face by its obvious companion "Big Willie." Connecting the eastern extremity of Big Willie with the north-west corner of the Quarries the Germans remained in possession of Potsdam Trench, while the Quarries themselves formed another but smaller salient in the enemy's lines, well flanked on the south-east side by our positions, which caused a second abrupt turn to the east in the enemy lines.
The whole area between these confused positions was a vast maze of earthworks, for they were in the midst of what had, prior to the battle, been a strong German third system of defence and No Man's Land was traversed by innumerable short communication trenches and saps, held by the opposing garrisons by means of barricades, for the possession of which an unceasing and murderous struggle with bombs and trench mortars was still proceeding. In addition to these deadly conflicts a still more subtle warfare was being waged underground, where our Tunnelling Companies were fighting a battle of wits with the Germans by mining and counter-mining, and the blowing of mines followed by fierce local infantry fights for possession of the craters thus formed were of frequent recurrence.
A reference to a large map will render clear the extreme importance to the enemy of the possession of these two positions. Situate as they were, one on each of the two lowest spurs of the Vermelles-Hulluch Ridge, their capture by the British would have involved a very serious threat to the German defences on the line Auchy-Haisnes, and might easily have been a prelude to the outflanking of La Bassée itself. The enemy was obviously alive to these possibilities, and the daily intelligence reports gleaned from our patrols and observers made it abundantly clear that he was strengthening his trenches and wire, and was burrowing strenuously in opposition to our mining operations.
This severely contested part of the front was taken over by the 47th Division from the 9th between the 13th and the 15th December, C Section opposite the Quarries and D Section opposite the Hohenzollern Redoubt being occupied by the 141st and 142nd Brigades, the 140th Brigade remaining in reserve.
For some time after the return to the line the 1/4th Londons did not enter the trenches as a battalion, but on account of its small numbers was retained in reserve, where it performed a great deal of heavy labour in working and carrying parties for the rest of the Brigade.
On the 15th the 1/4th Londons moved from Lillers at 8.30 a.m., entraining for Nœux-les-Mines, whence it marched to billets at Labourse, training being continued while the Brigade remained in reserve.
This move was followed by a further approach to the line which took place on the 19th December, when the 140th Brigade relieved the 141st in C 1 and C 2 Sections, opposite the Quarries, the 6th and 15th Battalions occupying the front trenches with the 7th Battalion in support at Le Philosophe and the 4th and 8th Battalions in Brigade reserve at Noyelles-les-Vermelles.