Two mines were laid at on the northern flank, one at St Eloi, three at Hollandscheschuur, two at Petit Bois, one each at Maedelstede Farm, Peckham House and Spanbroekmolen, four at Kruisstraat, one at Ontario Farm and two each at trenches on the southern flank. One of the largest of the mines was at Spanbroekmolen; Lone Tree Crater formed by the blast of of ammonal in a chamber at the end of a gallery long, below ground was in diameter and deep. The British knew of the importance the Germans placed on holding the salient, after a captured corps order from stating "that the salient be held at all costs" was received by Haig on 1 June. In the week before the attack, and howitzers bombarded the German trenches, cut wire, destroyed strongpoints and conducted counter-battery fire against German artillery pieces, using The 4th Army artillery consisted of fifty-four twenty-four guns, and four heavy and guns.