In 1941 Dunbar was commissioned by the War Artists' Advisory Committee to record hospital trains. Intended to provide emergency evacuation transport for victims of gas or bombing attacks, chiefly in London, they consisted of converted passenger carriages and - as in this sketch - guards' vans. Dunbar's sketch contains colour notes and observations in pencil. Human figures were later added to create Hospital Train, 1942, now in the collection of the Imperial War Museum.