With the advent of war Oliver quickly volunteered for the R.N.V.R. and is noted as having been promoted from Sub-Lieutenant to temporary Lieutenant in the London Gazette for 18 July 1916—at the same time Donald Maxwell received a similar promotion.
R.N.V.R. To be tempy. Lieut.- Tempy. Sub-Lieut. Digby E. Easton. 17th July 1916.
The undermentioned tempy. Sub-Lieuts. to be tempy. Lieuts.:- Ernest H. Oliver. 6th Apr. 1916. Thomas Sinclair. 17th June 1916. Donald Maxwell. 24th June 1916. William Robinson. 26th June 1916. To be tempy. Sub-Lieut.- Ernest T. Hall. 17th July 1916.
After the war, Oliver went back to Lloyd's, eventually becoming editor of Lloyd's Register of Yachts which position he held until 1936.