The month of July 1917 was spent in preparation for the Ypres offensive: the third battle of Ypres, known as the Battle of Passchendaele. The battle commenced on 31 July 1917. The role of the 18th Division was to leapfrog the 30th Division after they had taken what became known as "the Black Line" through Glencorse Wood. By mistake the 30th Division infantry wheeled to their left and assaulted Chateau Wood instead of Glencorse Wood. The misleading information that Glencorse Wood was in British hands caused the 53rd Brigade to plunge into a fatal gap. During 31 July and 1 August the 53rd Brigade fought against a fully prepared enemy for ground which the 30th Division should have taken. This error caused the offensive in Glencorse Wood to be held up for several days with fierce fighting throughout this period.