peel back from west to east, redeploying to block the main highway leading northeast through the Kaiserslautern Gap. Unfortunately for Foertsch's plan, the principal threat to the Kaiserslautern Gap came not from west or southwest but from northwest where Walker's XX Corps was pouring unchecked through General Walther Hahm's LXXXII Korps. The 10th Armored Division′s arrival at Kaiserslautern itself on 20 March meant not only that the gap was compromised by a force well in the rear of Knieß′' formations but also that the only way out for both Knieß′ troops and those of the adjacent XIII SS Korps was through the Pfaelzer Forest. As Knieß′ withdrawal progressed, it had the effect of opening a path through the Siegfried Line for the left wing of the U.S. Seventh Army. Despite a stubborn rear guard, the 63rd Division of General Milburn's XXI Corps broke through the main belt of fortifications near St. Ingbert late on 19 March. Had events moved according to plan, Milburn then would have sent an armored column northward to link with Walker's XX Corps near St. Wendel; but so swift had been the advance of Walker's troops that all worthwhile objectives in Milburn's sector beyond the Siegfried Line already had fallen. Milburn and his XXI Corps had achieved a penetration but had no place to go. The Seventh Army commander, General Patch, seized on the situation to provide a boost for his army's main effort, the attack of the XV Corps through Zweibrücken toward the Kaiserslautern Gap. In two days of hammering at General Simon's XIII SS Korps, the divisions of the XV Corps still had opened no hole through the Siegfried Line for armored exploitation. Send a combat command, Patch directed the XV Corps commander, General Haislip, to move through the 63rd Division's gap and come in on the rear of the Siegfried Line defenders facing the XV Corps. That the Americans would exploit the withdrawal was too obvious to escape the 1. Armee commander, General Foertsch. During the night of the 19th, he extended the authority to withdraw to the west wing of the XIII SS Korps. Thus, hardly had the American combat command begun to move early on 20 March to exploit the 63rd Division's penetration when the 45th Division of the XV Corps also advanced past the last pillboxes of the Siegfried Line near Zweibrücken. During the night of the 20th, the rest