Disher enlisted in the First AIF on 13 July 1917, and was commissioned as a Captain. He embarked for Europe on the HMAT Themistocles on 4 August 1917, and arrived at Glasgow on 2 October 1917. On 28 October 1917 he was sent to the Western Front, where he was assigned to the 5th Field Ambulance. On 16 March 1918 he was attached to the 4th Field Artillery Brigade as its Regimental Medical Officer. In March 1919, he was given leave to row in the AIF eight in the Henley Royal Peace Regatta. They won the King's Cup, defeating the Oxford University team in the final by a length. Disher received the 1919 Helms Award for the most outstanding amateur athlete from Australasia. He also took the opportunity for postgraduate study at hospitals in the UK under the Inter-Allied Fellowship of Medicine scheme from 23 July to 23 October 1919. He returned to Australia on the SS Nestor on 1 November 1919, where his AIF appointment was terminated on 22 January 1920.
Disher joined the Second AIF as a colonel on 8 December 1939, and was allocated the AIF service number VX294. Five days later he embarked for the Middle East on the SS Strathallan as part of the AIF Advance Party. He was ADMS of the AIF Advance Base until 4 April 1940, when he became ADMS of the 6th Division. He was awarded the Efficiency Decoration on 20 June 1940. He was in charge of the medical arrangements for the Battle of Bardia, for which he was mentioned in despatches, and made a Commander of the Order of the British Empire on 4 July 1941. His citation read: After serving in the Battle of Greece in April and May 1941, Disher embarked for Australia on 1 August 1941, where he became ADMS of the 1st Armoured Division. He was promoted to brigadier on 6 April 1942, and became Deputy Director of Medical Services of II Corps on 14 April 1942. On 30 November 1942 he took over as DDMS of New Guinea Force. As such, he was in charge of the medical arrangements during the Battle of Buna-Gona. He returned to Australia on 13 July 1943, and became Director of Medical Services of the First Army. He relinquished that appointment on 6 September 1944, and went on leave without pay. His AIF appointment was terminated on 21 June 1945, and he was transferred to the Reserve of Officers as a brigadier.
Later life
After the war, Disher retired from medicine and moved to an sheep and cattle grazing property on the shores of Lake Wellington in Gippsland that his grandfather had acquired in 1869, and of which he had become owner on the death of his father on 31 May 1944. Disher died at Sale on 13 March 1976, and his remains were cremated. He had no children, and his wife died on 8 June 1946. Disher bequeathed his estate at Strathfieldsaye, which was valued at around $588,500, along with its records, to the University of Melbourne, which established the Strathfieldsaye Institute of Teaching and Research in Agriculture and Allied Sciences. The records were transferred to the University of Melbourne archives. The Disher Challenge Cup, an annual rowing race for eight-oared boats on Canberra's Lake Burley Griffin that is contested by the Australian Defence Force Academy, the Royal Military College, Duntroon, and the Australian National University, was named in his honour; Disher presented the cup to the inaugural winners in 1971.