After breaking out of the bocage, VIII Corps was able to roll fifty miles in seven days, but it, and the remainder of Bradley's First Army, remained bottled up on the Cotentin Peninsula. The next phase of the fight, codenamed Operation Cobra was to break out of the peninsula, and once this occurred, Patton's Third Army would join the fight. The operation began on 24 July 1944 when American air commanders were asked to lay a carpet of bombs on the Germans to soften them up for the advancing ground forces. Poor weather curtailed the operation on the first day, but more than a thousand bombing missions were carried out the following day. Lieutenant General Lesley McNair, chief of the Army Ground Forces, came to Middleton's headquarters to witness the bombing. Middleton warned him to stay at corps headquarters, but McNair strayed away far enough that he and other members of his party were killed when they got caught by a stick of Allied bombs. More than 600 U.S. troops were killed or wounded in this friendly fire incident when the bombs fell short of their intended target.