On 5 May 1918, the AEF replaced the 1st Pursuit Organization Center at Toul-Croix de Metz Aerodrome, with the 1st Pursuit Group, the first American group-level fighter establishment (the 1st Corps Observation Group, organized in April 1918, was the first U.S. group). Major Atkinson became the 1st Pursuit Group's first commanding officer, followed by Major Harold E. Hartney on 21 August 1918. The 27th and 147th Aero Squadrons (Pursuit) were officially assigned to the group on 2 June, and the 185th Aero Squadron, a night pursuit unit, on 18 October.