During the American Civil War, All Saints Parish was led by Rev. Marmaduke M. Dillon, a Unionist who had served as an army officer. His pastorate was marked with friction among some of the parish's southern-sympathizing members. In the fall and winter of 1862-1863, the church was used as a field hospital during the Maryland Campaign, housing wounded soldiers from the Battles of South Mountain and Antietam. After the resignation of Rev. Dillon in 1866, the parish settled into a prolonged period of stability and growth under the leadership of Rev. Dr. Osbourne Ingle. He served as rector of All Saints' Parish from 1866 until his death in 1906, a span of 40 years. Dr. Ingles' eldest son, the Rev. James Addison Ingle, served as a missionary to China and as bishop in the Missionary District of Hankow.