The final plan of attack into Happy Valley and the surrounding terrain, codenamed Oklahoma Hills, called for the 7th Marines, reinforced, in coordination with the 51st ARVN Regt., to conduct the phased movement of three battalions into the area of operations, establishing fire support bases and landing zones, and conducting reconnaissance-in-force operations, destroying all enemy forces, caches, and installations. Simultaneously,, reconnaissance elements were to conduct screening operations to the north and west, as well as within the area of operations. A fourth Marine battalion would conduct screening operations south of Charlie Ridge, astride Route 4 and the Song Vu Gia, to prevent enemy troops from crossing into the Arizona area and vice versa, while a fifth Marine battalion would be available on 2 hours notice as a reaction and exploitation force if needed.
Preparatory operations directly in support of Oklahoma Hills began on 21 March with the advance of LT. Col. John A. Dowd's 1st Bn., 7th Marines west from Fire Support Base Rawhide (Hill 65) along Route 4. Assigned the mission of securing the route between Hill 65, and Hill 52, a distance of 10 kilometers, Dowd's Marines also were to establish a major fire support base, later named Mustang, at the latter site. Early on the morning of the 24th, Company C seized the hill and began local security patrols.
The following day, a platoon from Company B and a platoon of engineers from Company C, 1st Engineer Bn., began sweeping Route 4 of mines and upgrading the roadbed. By noon on the 26th, Hill 52 was secure and the 10-kilometer stretch of Route 4 between Hills 65 and 52 was clear and ready to support the heavy logistical traffic necessary to sustain Mustang. Engineer work on gun positions began on 28 March and by the 30th, Mustang was ready to receive Battery K, 4th Bn., 11th Marines, and a platoon of 8-inch howitzers.
It also would be necessary to relieve the 2nd and 3rd Bns., 7th Marines of their normal responsibility of patrolling the rocket belt west of Da Nang. (As Golf Co. was getting ready to leave Hll 22 another company showed up to take over. George Terry was fooling around with a grenade and pulled the pin. He tried to stick the pin back in but I told him not too, the grenade could still go off. So he tosses it into the wire, well away from everyone. Some Sgt. in the company that was replacing us threw a shit-screaming-running-fit. "How dare we endanger his men." It went on and on. He never really calmed down until we left a little later.) On the 29th, the 26th Marines assumed responsibility for the area controlled by the two battalions, as Col. Nichols ordered a number of final preparations for the operation. Among them was the establishment of an automatic retransmission site on R.C. Ba Na to provide adequate communicaions throughout the area of operations. The 2nd Bn., 7th Marines initially provided a security elements for the relay station, but as the operation progressed, and various battalions phased out, the 3rd Bn. 26th Marines followed by the 3rd Bn., 7th Marines provided this support.
Shortly after sunset on 30 March, Lt. Col. Neil A. Nelson's 2nd Bn., 7th Marines departed Hill 10 (FSB Stallion), and began moving on foot into the area of operations. Concurrently, the 3rd Bn. under Lt. Col. James O. Allison, who had relieved Lt. Col. Quinn on the 23rd, initiated a similar advance to the west from Hill 41. "This was a very unique move," recalled Capt. Paul K. VanRiper (Later Lt. Gen. VanRipper) Company M's commanding officer, "in that we took the whole company well up into the jungled mountains during the nightname. We moved out a 2000 and by early the next morning we were up under the canopy and the NVA forces in the area had no idea that we had moved this far and of our present location." As both battalions pushed westward, "searching out base areas, looking for caches, fortifications, any enemy that we could locate and destroying all of the same." Operation Oklahoma Hills began.
Events moved smoothly on the morning of the operation's first day, with all landing zone preparations, delivered by tubes of the 11th Marines, the Mullinnix, (DD 994), and later Newport News, (CA 148), completed on schedule. The lift by HMM-165 helicopters of the 2nd Bn., 51st ARVN Regt. into LZ Hawk (three kilometers northwest of the Thuong Duc CIDG Camp), and the 3rd Bn., 51st ARVN Regt. into LZ Eagle (three kilometers northwest of Thuong Duc), began at 1100 and was accomplished without incident within an hour. The following morning, Lt. Col. Edward W. Snelling's 3rd Bn., 26th Marines (BLT 3/26) assaulted, along with a 4.2 inch mortar battery from 1st Bn., 13th Marines, into LZ Robin, overlooking Happy Valley. These landings, coupled with the overland movement of the 2nd and 3rd Bns., 7th Marines on the night of the 30th, (We walked from dark until after morning, rested a while and kept moving. I think we made it up to Hill 502, LZ Buckskin, before we really stopped.) completed the introduction of all major allied units into the area of operations.
Confronted with the ever-present problem of helicopter availability, Col. Nichols deliberately decided to establish fire support bases initially around the periphery, instead of throughout the objective area. (So that's what we were doing!!!!! Now, they could have told us that. All I could tell at the time was that we walked a long ways and then set around for several days.) Additional bases would be established as the maneuver battalions moved beyond the range of their artillery support, and on prominent terrain fetures in anticipation of future operations in the area.