Reserve IR 99 of Reserve Infantry Brigade 52, holding the line north of Thiepval, was broken through and the attackers rushed Redoubt around The garrison, a support company standing by to reinforce the front defences, was surprised and surrendered after brief resistance. The centre battalion of RIR 99 had been destroyed in the breakthrough and taken prisoner. An attack towards the Grandcourt Line ran into the British barrage, then fell back to Redoubt and the which ran from the redoubt down the north edge of the ridge to the Ancre. The left hand battalion of RIR 99 had repulsed the attack on Thiepval but the centre and right, from the village to the Ancre south of St Pierre Divion, had been broken through, most of the troops having been trapped underground and taken prisoner. Observers in the Grandcourt Line were unable to see the breakthrough and over-running of the redoubt and the because of smoke and dust in the air. Only when the Irish advanced on the Grandcourt Line, was the identity of the troops visible in the area discovered. As soon as the British bombardment lifted, the only reserves nearby, the recruit battalion of IR 180 and a machine-gun company, occupied the Grandcourt Line around Thiepval.