He served in Gallipoli as part of the 29th Division. Like so many of his comrades, James Simpson suffered from diarrhoea almost constantly while he was on the peninsula. Fortunately this did not turn into dysentery, however his symptoms did worsen, giving him headaches, abdominal pain and a temperature, and all this was diagnosed as influenza and he was evacuated to the Hamrun Military Hospital on Malta.

The hospital environment did nothing for his condition and he failed to recover until he was transferred to England aboard the hospital ship HMHS Asturias, for a period of four months, now with a diagnosis of neurasthenia and dyspepsia. HMHS Asturias was the ship on which the author JRR Tolkien was evacuated from France aboard when as a 2nd Lieutenant he contracted Trench Fever. The Asturias was torpedoed during the war and some of her crew killed, but the ship survived and became a tourist cruise ship.

While in England he was a convalescent at 3rd Northern Hospital at Sheffield. On his recovery he was sent back to his unit, which by this time had been evacuated from the Gallipoli Peninsula and were now serving on the Western Front. James Simpson died of wounds at 87th Field Ambulance, the 29th Division's field ambulance. The field ambulance was the second link in the evacuation chain, in between the regimental aid post and the casualty clearing station, and so if a man died here it is likely that he was very recently wounded and too seriously wounded to have been sent back to the C.C.S.

Lieutenant Simpson’s death was announced in the Yorkshire Evening Post on Wednesday 12^th July 1916 and featured a photograph of him in the solar helmet issued to troops in the Mediterranean Theatres.