The blueprints for a major Allied drive into the Khe Sanh Plateau had been on the drawing boards at III MAF Headquarters in the embryo stage since late January. The 1st ACD was slated for the campaign since that division had displaced from Bong Son, in II Corps, and arrived at Phu Bai on 22 January. Three days after he assumed operational control of the new division, General Cushman directed General Tolson to prepare a contingency plan for the relief of Khe Sanh. This action eventually resulted in Operation PEGASUS but there was a series of events which delayed its start until April. The first was the disruptive Communist TET Offensive and the resulting Battle of Hue City which raged until 25 February. Throughout February and early March, the 1st ACD was busily engaged in and around the old imperial capital. Logistics was another consideration. General Westmoreland had initiated a supply build-up in I Corps during December 1967 but III MAF did not yet have sufficient stock levels to support an operation the size of PEGASUS, especially while the heavy fighting still continued in Hue. Finally, the poor weather prevented large-scale helicopter operations in the Khe Sanh area.(200) An alteration of the command structure in I Corps also indirectly affected the proposed operation. Until the early part of 1968, the three divisions in I Corps (1st MarDiv, 3d MarDiv, and the U. S. Army Americal Division) were under the direct control of General Cushman, CG, III MAF. General Westmoreland, however, was convinced that a critical, if not the most critical, phase of the war was taking shape in I Corps and had begun to pump reinforcements into the two northern provinces. These included the 1st ACD and the 101st Airborne Division. To keep closer tabs on the action in the north, General Westmoreland also established a forward echelon of his MACV Headquarters, under the Deputy, ComUSMACV, General Creighton W. Abrams, at Camp Hochmuth, Phu Bai on 9 February. There was little formal change in the command structure; General Abrams simply acted as an agent for ComUSMACV in an advisor/coordinator role. On 10 March, however, the structure did change; MACV Forward was converted to Provisional Corps, Vietnam (PCV) and placed under the operational control of General Cushman, CG, III MAF. PCV's new commander, Lieutenant General William B. Rosson, U. S. Army, assumed control of all American combat forces operating in the northern two provinces, less the southern portion of Thua Thien. At that time the three major U. S. units in the area were the 3d MarDiv, the 1st ACD, and the 101st Airborne Division. In addition, the reinforced ARVN 1st Division was operating in this region. In essence, PCV was established to provide closer supervision over growing U. S. forces and coordination with the Vietnamese units in the northern area.(201)