Ernest Cambridge enlisted in June, 1914. He was then just over 18 and an assistant in the Mail Branch of the Melbourne GPO. He had some previous experience, having served with the Senior Cadets 51 Battalion at Albert Park for two years. Following initial training, he embarked on 1 April, 1916, on board HMAT Suffolk A23.

On 16 September, he was discharged because of his mother's illness, re-enlisting on January 12, 1915. He trained in Bendigo and was sent to France, where he joined the 1st Anzac Wireless Section. On December 19, 1917, he was transferred to the 4th Division Signals. In 1918, he was hospitalised with a septic foot, and given leave in the UK. Following this, he went AWL for a week, given seven days punishment and forfeiting 15 days' pay. He was returned to Australia on the Port Napier on May 12, 1919.