in the summer of 1944 during the Battle of Cherbourg, Battle for Caen, and the ultimate breakout from the beachhead, Operation Cobra. Unlike Eighth Air Force, whose units stayed in the United Kingdom, Ninth Air Force units were very mobile, first deploying to France on 16 June 1944, ten days after the Normandy invasion by moving P-47 Thunderbolts to a beach-head landing strip. Because of their short range, operational combat units would have to move to quickly prepared bases close to the front as soon as the Allied ground forces advanced. The bases were called "Advanced Landing Grounds" or "ALGs". On the continent, many ALGs were built either from scratch or from captured enemy airfields throughout France, the Low Countries and Germany. Ninth Air Force units moved frequently from one ALG to another. By early August most Ninth Air Force operational fighter and bomber groups were transferred to bases in France and assigned to the U. S. Twelfth Army Group. These groups were then assigned to Tactical Air Command (TAC) organizations which supported Army ground units. XXIX Tactical Air Command (XXIX TAC) was activated in France on 15 September 1944, commanded by Brig. Gen. Richard E. Nugent, to support operations of the U.S. Ninth Army. XXIX TAC supported the Ninth Army in the north; IX TAC supported the First Army in the center; and XIX TAC supported the Third Army in the south. Air cover over Allied-controlled areas on the continent was performed by the IX Air Defense Command. Ninth Air Force groups made numerous moves within France, the Low Countries and western Germany to keep within range of the advancing battle front before the end of hostilities in May 1945. During Operation Dragoon, the invasion of Southern France in August 1944, two Ninth fighter groups were transferred to the provisional United States/Free French 1st Tactical Air Force supporting the invasion force's drive north. As part of Operation Market-Garden, the Ninth Air Force transferred its entire IX Troop Carrier Command with its fourteen C-47 groups to the 1st Allied Airborne Army in September 1944. Those troop carrier groups flew many of the C-47s and towed CG-4 Waco gliders for the Allied airborne unit drops—Operation Market Garden—to take the bridges northwest of Eindhoven at Son (mun. Son en Breugel), Veghel, Grave, Nijmegen and Arnhem in the Netherlands. In December 1944 through January 1945, Ninth Air Force fighters and bombers were critical