Following the outbreak of the First World War, the 5th Brigade was re-raised in mid-1915 as part of the Australian Imperial Force (AIF) from volunteers for overseas service. Upon formation it consisted of four infantry battalions—the 17th, 18th, 19th and 20th Battalions. Assigned to the 2nd Division, the majority of its personnel were drawn from men that had previously served in New Guinea with the Australian Naval and Military Expeditionary Force. After formation, the brigade departed Australia, embarking for Egypt, in May 1915, and after a period of training, were dispatched to Gallipoli in August as reinforcements for the 1st Division, which had been there since April. The brigade subsequently took part in the August Offensive, as the Allies sought to break the deadlock that had descended on the peninsula. After the offensive failed, the 5th Brigade remained at Gallipoli, undertaking mainly defensive tasks until they were evacuated in December 1915 and withdrawn back to Egypt. In early 1916, the brigade was sent to France as part of the large-scale transfer of the AIF's infantry divisions to the European battlefield. For the next two-and-a-half years the 5th Brigade fought on the Western Front, taking part in numerous battles.