It was some time before the garrison of Triangle Support could be overcome, as only one second-wave tank on the battalion front managed to cross the Hindenburg front line. Subsequently the resistance collapsed on the arrival of some third-wave tanks, but not before odd platoons had gallantly fought their way into the trench. Wood Trench and Mole Trench were occupied without particular effort; but beyond Mole Trench lay a sunken road, into which large numbers of the enemy had fled at the first sight of the tanks. This road was cleared with the assistance of a tank, which did magnificent execution with its 6-pounder gun, shell after shell bursting in the midst of parties of panic-stricken Germans. By this time the 7th Black Watch, who were detailed to pass through the 5th Gordon Highlanders for the second phase of the attack, came up, and with some of the latter crossed the Grand Ravine and moved towards Chapel Trench. Here again the Germans fought stubbornly, some 40 of them being killed before the trench was occupied. The 5th Gordon Highlanders thus arrived on their objectives, having captured a total of 10 machine-guns, 2 trench-mortars, and 400 prisoners, including a battalion commander complete with his staff. So far the attack had proceeded smoothly enough, but in the next phase the conditions under which the advance was to be carried out changed considerably. Up to the present the main difficulty of the tanks had been the width and depth of the trenches which they had to traverse, effective action against them on the part of the enemy having been negligible. In the next stage the advance was to be carried out through the enemy's gun line, with the result that the tanks had not only to contend with the crossing of the trenches, but were also exposed to the close-range fire of field-guns. As the infantry depended absolutely and entirely on the tanks for the crushing of the large belts of wire opposed to them, any losses sustained by the tanks, as will be seen, seriously prejudiced the infantry's chances of success. The enemy's support system, which was to be overcome in the next bound, consisted of a strong fire-trench known as the Hindenburg Support, protected by two to four belts of heavy wire, and supported by a trench some 100 yards in rear known as Flesquières Trench--a trench in many places shallow, and protected by little wire. Of these the former lay on the crest of the Flesquières Ridge, and the latter just behind it. Both skirted a chateau at the south-west corner of the village, which, with its walls and wooded grounds, offered great possibilities for concealed defences.