William Falkingham enlisted early, on the 14 October, 1914. He was then eighteen years old and had the consent of his father, Henry Falkingham. He had had 12 months in the School Cadets and a further 3 years Compulsory Military Training. He was not employed. He did four months training with the 3rd Light Horse, before moving to the 6th Field Ambulance on 29 January, 1915, and then in March was attached to the 1st Australian Field Ambulance.

He was sent overseas on 31 March, 1915, and went for duty at Sarpi camp, Mudros. In August that year, he was ill and sent first to the Australian Military Hospital at Valetta, Malta, and then to Birmingham, England, to the Southern General Hospital at Portsmouth, before returning to his unit at Mudros in November, 1915. In December, he was attached to the 3rd Field Ambulance at Anzac and sent to the Advanced Base Medical Store. From there, he was taken on strength with the 14th Battalion in France, but again, fell ill with influenza in April, 1916, and was then reported wounded in action, with shell shock on 13 August, 1916 and again hospitalised.

He was wounded in action with a gunshot wound to his right thigh in September, 1916. Again returned to the front, he was ill with influenza in February, 1917 and with mild rheumatism in June, 1918, and in both cases, sent to hospital. This history may explain the nine charges of being Absent Without Leave, the first in May, 1917, for which he was court-martialled in June, the others following his bouts of illness. He was discharged from service on 24/1/1917 and returned to Australia.