On 14 September 1944, the 393d Bomb Squadron arrived at Wendover from its former base at Fairmont Army Air Base, Nebraska, where it had been an operational training unit (OTU) with the 504th Bombardment Group since 12 March. When its parent group deployed to the Marianas in early November 1944, the squadron was assigned directly to the Second Air Force until creation of the 509th Composite Group on 17 December 1944. As part of the formation of the 509th, about 800 people stationed at the field, were transferred to the new group. To make the 509th Composite Group as self-contained as possible, other units were assigned, including the 390th Air Service Group, with the 603d Air Engineering and 1027th Materiel Squadrons; the 320th Troop Carrier Squadron, known as the "Green Hornet Airlines"; the 1395th Military Police Company, and later the 1st Ordnance Squadron. A Manhattan Project unit, the 1st Technical Detachment, was attached to the group.