 Although superseded as head of the project by Brigadier General Leslie R. Groves Jr., in September, he was Manhattan District engineer from 13 August 1942 to 13 August 1943.In November 1943 he became Assistant Chief of Staff (G-4) of the United States Army Services of Supply (USASOS) in the Southwest Pacific Area, serving in Australia, New Guinea and the Philippines.Marshall left the Army in 1947, and moved to Riverside, Connecticut, where he worked for M. W. Kellogg.