Complex sentence: He returned to the United States to serve in Office of the Director of Military Aeronautics in Washington, DC from 1 August to 23 September 1918, then went to England to take command of the United States Army Air Service Camp at Codford.
Split into simpler sentences: He returned to the United States to serve in Office of the Director of Military Aeronautics in Washington, DC from 1 August to 23 September 1918. After this posting he went to England to take command of the United States Army Air Service Camp at Codford.