Aubrey, the son of Alfred and Alice Hapgood, was born at Nowra NSW in 1897. About 1907 his family came to Inverell where they had a dairy farm just north of the town. Aubrey enlisted at Inverell on 10 January 1916, possibly at the huge recruiting rally held in Victoria Park when the First Contingent of The Kurrajongs were presented with their Inverell Medals. He was a nineteen year old farmer and had completed two years of military training.
With seventeen other recruits, he departed Inverell on 1 February 1916, joining the 33rd Battalion, B Company, and sailing from Australia on HMAT A74 Marathon on 4 May. After arriving in England he attended a Trench Mortar School at Perham Downs before going to France in November.
In July 1917 Aubrey was wounded during the Battle of Messines and awarded the Military Medal for conspicuous courange in superintending the evacuation of wounded men. In March the following year he received a gunshot wound to his shoulder which required treatment in England.
Three months later he returned to France and rejoined the 9th Light Trench Mortar Bomb unit. During December Private Hapgood was awarded a Bar to his Military Medal. He returned to Australia in September 1919 and married Alice Sweaney at Inverell in 1921.