First Marine Division OpnO 6-51, issued on 20 February, directed the two assault regiments, the 1st and 5th Marines, to jump off at 0800 on the 21st and seize the first objective, the ridgeline about three and a half miles south of the high ground dominating Hoengsong (Map 6). RCT-1, with Division Recon Company and C/Engineers attached, was to pass through elements of the 2d Infantry Division in zone while RCT-5, with A/Engineers attached, passed through elements of the 187th Airborne Infantry, USA. RCT-7 had been designated the reserve regiment; but since it could not arrive from the Pohang-Andong area in time, a battalion of the 5th Marines was assigned this mission.[93] [93] _Ibid._, 2, 22, and 1stMarDiv OpnO 6-51. The objective area was believed to be defended by the 196th Infantry Division of the 66th CCF Army and unknown elements of the 39th and 40th CCF Armies. Ahead of the Marines and other IX Corps units lay some uninviting terrain. Rocky heights and narrow valleys were laced by swift streams, the largest being the river Som, running from northeast to southwest through a defile cutting across the western part of the Division sector. Bordering this twisting stream was the Wonju-Hoengsong “highway”--a poor dirt road even by Korean standards. Through the right half of the Division zone an even more primitive road, scarcely fit for vehicular traffic, wound northeast from Wonju.[94] [94] _Ibid._, 22–24. All Eighth Army forces were to be tightly buttoned up and to keep in close physical contact while maintaining integrity of units. Patrol observation and reconnaissance were stressed by the EUSAK commanding general, and even lack of opposition would not justify a unit in advancing ahead of schedule. Again, as in previous operations, real estate was to be secondary to the inflicting of maximum personnel and materiel damage. On the eve of Operation KILLER, a message from IX Corps emphasized to all units the necessity for making sure “that no hostile force of sufficient strength to jeopardize the safety of your forces has been bypassed. Maintenance of lateral contact between all units is of prime importance.”[95] [95] IX Corps msg in 1stMarDiv _In&Out#9_. Marine ground force and aviation officers alike realized that the forthcoming offensive would be the first real test of the operational control of the 1st MAW by the Fifth Air Force and the Eighth Army. General Smith was uneasy about the outlook. On 13 February 1951, the day he was alerted for the move to Chungju, he had requested in a message to EUSAK that the 1st MAW be assigned to the support of his division. Both Marine ground and air officers, he said, believed that this change would fit into the JOC overall air control system without any disruption.[96] But no approval of General Smith’s proposal had been received before D-Day. [96] CG 1stMarDiv, msg of 12 Feb 51 to CG EUSAK. _The Jumpoff on 21 February_