the retention of ground currently held were essential features of Eighth Army operations as Ridgway conceived them. "Terrain," he maintained, "is merely an instrument... for the accomplishment of the mission here," that of inflicting maximum losses on the PVA/KPA at minimum cost while maintaining major units intact. Intelligence indicated that those forces giving ground before the Killer advance in the IX and X Corps' zones were moving into defensive positions just above the Arizona Line. Eighth Army intelligence officer Colonel Tarkenton, believed these forces would tie in with the existing PVA/KPA front tracing the north bank of the Han River in the west and passing through the ridges above Route 20 in the east. Lending support to this judgment, the PVA 39th Army had moved up on the line in front of IX Corps, and the KPA III Corps, less its 3rd Infantry Division, had entered the line before X Corps. Thus, as of 1 March six PVA armies and four KPA corps were arrayed between Seoul and the spine of the Taebaek Mountains. On the 1st, as he had earlier, Colonel Tarkenton carried the PVA 37th Army in his enemy order of battle, locating it immediately behind the center of the PVA/KPA front in the vicinity of Chuncheon. In his earlier estimate he tentatively had placed the 43rd Army in the same area, but had since decided that this unit was not in Korea at all. Tarkenton now also had reports that two PVA armies, the 24th and 26th, had moved south from the Hungnam-Wonsan region to a central assembly just above the 38th Parallel north of Chuncheon. Thus three reserve armies might be immediately available for offensive operations in the central region. To add substance to this possibility, agents recently returning from behind enemy lines brought back reports that the PVA/KPA high command at one time had planned to open an offensive on 1 March, then had postponed the opening date to the 15th. During interrogation, recently taken prisoners of war partially substantiated the agent reports by stating that their forces were preparing to launch an offensive in the Eighth Army's central zone early in March. It also now appeared that the KPA VI Corps, one of the units that had withdrawn into Manchuria the past autumn, had returned to Korea and was moving toward the front in the west. At last report the VI Corps, or a