 The II Anzac Corps objective was the southern part of the ridge and Messines village . The 3rd Australian Division on the right , had been disorganised by a German gas bombardment on Ploegsteert ( Plugstreet ) Wood around midnight , which caused 500 casualties during the approach march but the attack between St. Yves and the river Douve began on time . The 9th and 10th Brigades benefitted from four mine explosions at Trenches 122 and 127 , which were seven seconds early and left craters 200 feet ( 61 m ) wide and 20 feet ( 6 @.@ 1 m ) deep . The craters disrupted the Australian attack formation , some infantry lines merging into a wave before reforming as they advanced . The New Zealand Division approached over Hill 63 and avoided the German gas bombardment . The two attacking brigades crossed the dry river bed of the <unk> and took the German front line , despite the abandonment of the mine at La Petite Douve Farm and then advanced towards Messines village . On the left of the corps , the 25th Division began its advance 600 yards ( 550 m ) further back than the New Zealand Division but quickly caught up , helped by the mine at Ontario Farm . 
