Benjamin James McDonald was 18 years and 9 months old when he enlisted to serve in the Great War. He was under age, but the authoritites accepted his application without dispute. In his enlistment form, he wrote that both his parents were dead and gave his next of kin as his sister, Eva McDonald, then living at 17 Clarendon St., East Melbourne, at St Hilda's Missionary Training Home, run by the Anglican Church. He gave his next of kin as Mrs. Mooney, at 102 Ferrars St., South Melbourne, but there is no explanation of who she was or what relationship she had with him. Perhaps she ran a boarding house where he lived. He was working as a Ship's Steward prior to enlisting.

 He signed up 23rd of February, 1916 and went for training at Seymour. However, on 1 June, 1916, he went A.W.O.L. not returning to camp until, 21 June. He re-enlisted in August, 1916,  and was sent back for training at Seymour and then at Langwarren from 22nd August to 7th of December and was assigned to the 37th Battalion 1-6th Reinforcements. On 16 December, the new recruits set sail for England on board H.T. Medic, disembarking at Plymouth on 18 February, 1917. On 3 March, Ben McDonald was sent to camp at Sutton Mandeville, first with the 14th Training Battalion , then transferred to the 66th Battalion at Windmill Hill. 

The 37th Battalion had been formed in February, 1916, as part of the 10th Brigade of the 3rd Australian Division. After training in Australia and Britain, the battalion moved to France on 23 November, 1916. By the next week and in the bitter months of a European winter, and were heavily involved in raids on the German lines.  

 From England, Benjamin McDonald was sent to France, landing on 22 August 1917 and marching out to camp on 31 August, 1917. On 8 September, he was taken on strength with the 37th Battalion. The 1st Battle of Passchendaele was just beginning and on 13 October, Benjamin McDonald was wounded in action with a bullet wound through his right ear. He was picked up by the 11th Ambulance Unit and taken to the nearest Casulaty Clearing Station . on 13 October, he was sent back to England on H.T. Princess Elizabeth  with a gunshot wound to his head, but it is unclear whether this was a second wound or the original wound to the ear. He weas ddmitted to the Central Military Hospital, Cheltenham, his injury described as a Gun Shot Wound to the scalp, so presumably it was largely a skin injury, not going through to the skull or brain.

Benjamin McDonald stayed in hospital for three weeks, then was sent to the No 2. Command Depot, prior to being returned to Australia. He embarked on H.M.A.T. Euripides on 21 January, 1918, and was discharged fomr further service on 13 July, 1918. His medals - the British War Medal, the Victory Medal and the 1914-1915 Star, were sent to him at 103 Princess St., Port Melbourne, but returned to the Department on 10 May, 1924.