Along the top of the ridge were several “tunnels,” which gave cover to a large number of troops. Just south of Sanctuary Wood, Tor Top Tunnels, a huge underground cavern lit by electric light, held the whole of the battalion in reserve to the left brigade. As there were only four exits from this place, so that very few men might have escaped if a fire had broken out, great precautions were taken, and nobody was allowed even to strike a match. These orders were the outcome of a disastrous fire which had occurred in Hedge Street Tunnels the night before the 61st Brigade went into the line, when several officers and men were burnt to death, including some of the advanced party of the 61st Brigade. The swampy ground along the banks of the various streams which crossed the line was generally impassable, so that it was sufficient to organise the spurs for defence, and to wire the gaps in the line where the streams flowed through. For the first half of January, however, the hard frost made it possible to move across these marshes, and constant patrolling was necessary to ensure the safety of the line. Almost the only events which involved any fighting occurred on the night of the 9th/10th of January. In order to assist some operations of the 37th Division, the 20th carried out a demonstration in which artillery, Stokes mortars, machine guns, Lewis guns and rifle grenades all played a part. The 37th Division raided the enemy’s trenches twice during the night, and on both occasions the enemy put down a heavy barrage for an hour on the front and support lines of the 20th Division. At 4.45 A.M. on 10th of January a party of the enemy, estimated at 30 to 50 strong, attempted to raid the left company of the 6th K.S.L.I. in the left sub-sector. The forward posts were temporarily driven in, but the positions were quickly retaken, and though the Germans failed to capture any of the K.S.L.I., they left two of their own party prisoners in our hands. About this time the 37th Division on the right was relieved by the 4th Australian Division. On the 22nd of January the artillery of the 37th Division was relieved by that of the 20th, which from that date formed the Northern Group, under Major H. Price Williams, M.C. The battery positions extended between Zillebeke and Hooge. It was laid down that the policy of the artillery in this sector should be defensive and not aggressive, as it was not desired to stir the enemy into activity without good cause. Accordingly, while no favourable opportunity of inflicting loss on the enemy was missed, no harassing fire or fire without a definite object was carried out.