Williams was promoted to Major general on 26 August, shortly after returning to the European Theater to resume command of the IX Troop Carrier Command. While he had been away, operational control of IX Troop Carrier Command had been transferred from the Allied Expeditionary Air Force to the First Allied Airborne Army, a newly formed formation under Brereton's command. On 10 September Brereton held a conference with his troop carrier and airborne commanders and their staffs at his headquarters at Sunnyhill Park, near Ascot, Berkshire, where they were briefed on Operation MARKET, an airborne operation to seize a series of bridges in the Netherlands to enable the 21st Army Group to cross the Rhine River. At the conference Williams was given operational control of the Nos 38 and 46 Groups RAF, which he would exercise from his command post at Eastcote.