KHE SANH VALLEY] The KSCB sat atop a plateau in the shadow of Dong Tri Mountain and overlooked a tributary of the Quang Tri River. The base had a small dirt airstrip, which had been surfaced by a U. S. Navy Mobile Construction Battalion (Seabees) in the summer of 1966; the field could accommodate helicopters and fixed-wing transport aircraft. Organic artillery support was provided by Battery F, 2/12 (105mm), reinforced by two 155mm howitzers and two 4.2-inch mortars. The Khe Sanh area of operations was also within range of the 175mm guns of the U. S. Army's 2d Battalion, 94th Artillery at Camp Carroll and the Rockpile. In addition to B/1/9 and the CIDG, there was a Marine Combined Action Company (CAC) and a Regional Forces company located in the village of Khe Sanh, approximately 3,500 meters south of the base.[3] All these units sat astride the northwest-southeast axis of Route 9 and had the mission of denying the NVA a year-round route into eastern Quang Tri Province. The garrison at Khe Sanh and the adjacent outposts commanded the approaches from the west which led to Dong Ha and Quang Tri City. Had this strategic plateau not been in the hands of the Americans, the North Vietnamese would have had an unobstructed invasion route into the two northern provinces and could have outflanked the Allied forces holding the line south of the DMZ. At that time, the Americans did not possess the helicopter resources, troop strength, or logistical bases in this northern area to adopt a completely mobile type of defense. Therefore, the troops at the KSCB maintained a relatively static defense with emphasis on patrolling, artillery and air interdiction, and occasional reconnaissance in force operations to stifle infiltration through the Khe Sanh Plateau. In the event a major enemy threat developed, General Walt could rapidly reinforce the combat base by air.(7) On 20 April 1967, the combat assets at KSCB were passed to the operational control of the 3d Marines which had just commenced Operation PRAIRIE IV. The Khe Sanh area of operations was not included as a part of PRAIRIE IV but was the responsibility of the 3d Marines since that regiment was in the best position to oversee the base and reinforce if the need arose. The need arose very soon.(8)