Hindenburg Line. In early April, as a preliminary to the First Battle of Bullecourt, the 13th Brigade was thrown into an attack around Noreuil, during which the 49th was initially placed in brigade reserve, before putting in an attack that captured a railway cutting on the Cambrai–Arras line. Its next significant action came in June, after the AIF was transferred to the Ypres sector in Belgium, where a large salient had formed in the line. On 7 June the 49th joined the Battle of Messines where it advanced on the 13th Brigade's right, past Despagne Farm, into the Blauwepoortbeck Valley where they encountered German pillboxes for the first time. The German machine-gun fire was so intense that heavy casualties were suffered in the initial attack, particularly amongst the officers with every company commander killed. By the end of the battle, the 49th had suffered 379 casualties, with many being inflicted by their own artillery which had fallen on them during a German counterattack on 8 June. Further fighting was experienced in late September at Polygon Wood during the Third Battle of Ypres, as part of follow on actions after the success at Menin Road. The Australians wintered in Belgium during which time they undertook mainly defensive actions as they held various positions along the line, but in early 1918 they were moved south to the Somme Valley. Following the collapse of Tsarist Russia in late 1917, the Germans were able to transfer large amounts of equipment and manpower from the Eastern Front to the Western Front and subsequently launched their Spring Offensive in March. Falling on the southern flanks of the sector held by the British Third and Fifth Armies, the offensive initially succeeded in driving the Allies back and in late March, as the Germans closed in on the vital railhead around Amiens, the five Australian divisions, which had been grouped together as part of the Australian Corps, were transferred to the Somme to help blunt the attack. The 4th Division took up positions around Dernancourt, along the River Ancre, and on 5 April played a significant part in repelling a German attack there during the Second Battle of Dernancourt, where in the words of author Chris Coulthard-Clark, the 4th Division "faced the strongest attack mounted against Australians during the war". For their part, the 49th Battalion, supported by part of the 45th, put in a vital counter-attack late