When the surprise attack on the Ardennes took place on 16 December 1944, starting the Battle of the Bulge, the front of the U.S. 12th Army Group was split, with the bulk of the U.S. First Army being on the northern shoulder of the German 'bulge'. The Army Group commander, General Omar Bradley, was located south of the penetration at Luxembourg and command of the U.S. First Army became problematic. Montgomery was the nearest commander on the ground and on 20 December, Eisenhower (who was in Versailles) transferred Courtney Hodges' U.S. First Army and William Simpson's U.S. Ninth Army to his 21st Army Group, despite Bradley's vehement objections on national grounds. Montgomery grasped the situation quickly, visiting all divisional, corps, and army field commanders himself and instituting his 'Phantom' network of liaison officers. He grouped the British XXX Corps as a strategic reserve behind the Meuse and reorganised the US defence of the northern shoulder, shortening and strengthening the line and ordering the evacuation of St Vith. The German commander of the 5th Panzer Army, Hasso von Manteuffel said: