Derwent was educated at the Sheffield Royal Grammar School, at King Edward VII’s School at Sheffield, at Giggleswick School, and at the University of Sheffield. He obtained a commission as Lieutenant in the R.A.M.C., Territorial Force in December 1914, then continued for some weeks as Medical Officer at King George V’s Hospital, Dublin. He entered the war in France on 15th February 1915, and was attached to 84th Field Ambulance, but on the 9th March was lent as a temporary Medical Officer to the 1st Bn Cheshire Regiment. On the morning of 10th March 1915, while Derwent was in his dressing station, a message came through that an officer was bleeding to death in a trench. Derwent, along with an orderly (Pte J Needham of the 1st Cheshires), volunteered to go to him, and about 10.30 a.m. crossed the danger zone. When they reached the trench it was about 3 ft. deep and half full of water. Derwent attended to the wounded officer but rifle fire prevented them from getting him back to the dressing station, and so Derwent and Pte Needham stayed with the wounded officer in the trench for many hours. About 6 p.m. they made an attempt, however the wounded officer received a further wound and Derwent was shot in the lung. He died four days later, at St. Eloi, in spite of the utmost efforts made on his behalf by his colleagues, Capt Bickerton and Lt Haynes. Pte J Needham received the D.C.M. for his conduct on this occasion. Lt/Col W Salisbury Sharpe, R.A.M.C. wrote: “I do not know what form official recognition will take, but I can assure you of my personal appreciation that no greater instance of herioc self-sacrifice will be recorded during the war.” Capt R E Bickerton R.A.M.C. wrote: “The stretcher-bearers of my section have spoken very, very kindly of him and admired his pluck, saying that he never let them cross a risky part of the road without being there himself.” Derwent was the fifth son of William Perverill Turnball of Burway House, Church Streeton, co. Salop, late H M Divisional Inspector of Schools, by his wife, Fanny, daughter of the late Edwin John Hayes, Town Clerk of Birmingham.