H.C. Armstrong was groomed by Peter Ainslie for the leadership of the Association for the Promotion of Christian Unity, the new name of the Council on Christian Union as of 1916. The two met when Armstrong was a student at Yale and Ainslie delivered the Yale Lectures. They were mutually impressed with each other. Armstrong moved to Baltimore for pastoral ministry at Harlem Avenue Christian Church and eventually to Ainslie’s staff at Christian Temple where his assignment was full-time responsibility for the Association. In 1924, Ainslie resigned as president of the Association to form the Christian Unity League, and H.C. Armstrong became its secretary. He provided crucial leadership to the Association during a time of severe internal stress within the Disciples of Christ. The transition, even the survival of the Council, can be credited to the leadership of H.C. Armstrong.

H.C. Armstrong, Secretary, Association for the Promotion of Christian Unity, 1925-1931