The 21st Army Group initially controlled all ground forces in Operation Overlord. The 21st Army Group main components were the British 2nd Army and the First Canadian Army. Also included were Polish units and from Normandy onwards and small Dutch, Belgian, and Czech units. However the Lines of Communications units were predominantly British. Other Armies that came under command of 21st Army Group were the First Allied Airborne Army, the U.S. First Army for Overlord, and the U.S. Ninth Army; as a result of the disruption to the chain of command during the Battle of the Bulge and as reinforcement for the drive to the Rhine, Operations Veritable and Grenade. The U.S. Ninth Army again and the U.S. XVIII Airborne Corps were under command for the Rhine river crossings Operations Plunder and Varsity.