 Dun's principal work was as a civilian chaplain to the service men; the parish assisted him as they could.During the war, union services of the Federated, Unitarian, and St. Andrew's parishes were held at the YMCA on West Main Street in Ayer.After what must been an exhausting year and a half as vicar, he left in the spring of 1919 to continue his studies at the Universities of Oxford and Edinburgh.