After returning to Egypt, the AIF underwent a period of reorganisation as it was expanded from two infantry battalions to five prior to their transfer to Europe. As the battalion was rebuilt, further training was undertaken before it was sent to France, arriving there in late March 1916. For the next two-and-a-half years they participated in most of the main battles fought by the Australians on the Western Front. Their first major action came at Pozières in mid-1916 as part of the wider Battle of the Somme, being committed twice in July and August. In late August, the 18th was withdrawn to Belgium to recover, before returning to the Somme in October. For the rest of 1916, the battalion undertook defensive duties along the front, although they were not involved in any major attacks. The following year, the Germans shortened their lines and withdrew to the Hindenburg Line, after which the 18th Battalion took part in the fighting around Warlencourt in February 1917 as the Allies sought to follow up the German withdrawal. A brief advance followed before they came up against the forward positions of the Hindenburg Line. In May, the 18th Battalion was committed to the Second Battle of Bullecourt before moving again to Belgium where they saw further action around the Ypres Salient at Menin Road in September and Poelcappelle in October before settling down for the winter.