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 in the afternoon amidst heavy rain, which saved the situation for the Australians, whose line had been penetrated by a German counterattack across a railway bridge west of the town; in doing so they suffered heavily, though, losing 14 officers and 207 other ranks. Later in the month, they took part in the Second Battle of Villers-Bretonneux, launching an Anzac Day attack that successfully recaptured the town, which had been lost the previous day following an attack by four German divisions.