During the remainder of 1966 and in the first quarter of 1967, the intensity of fighting in the eastern DMZ area increased. Each time the enemy troops made a foray across the DMZ, the Marines met and defeated them. By 31 March 1967, the NVA had lost 3,492 confirmed killed in action (KIA) in the northern operations while the Marines had suffered 541 killed. For the Communists, it appeared that direct assaults across the DMZ were proving too costly--even by their standards.(5) [Illustration: MAP 2 E.L. WILSON NORTHERN QUANG TRI PROVINCE] The Khe Sanh Plateau, in western Quang Tri Province, provided the NVA with an excellent alternative. The late Doctor Bernard B. Fall compared the whole of Vietnam to "two rice baskets on opposite ends of a carrying pole." Such being the case, Khe Sanh is located at the pole's fulcrum in the heart of the rugged Annamite Range. Studded with piedmont-type hills, this area provides a natural infiltration route. Most of the mountain trails are hidden by tree canopies up to 60 feet in height, dense elephant grass, and bamboo thickets. Concealment from reconnaissance aircraft is good, and the heavy jungle under-growth limits ground observation to five meters in most places. Dong Tri Mountain (1,015 meters high), the highest peak in the region, along with Hill 861 and Hills 881 North and South dominate the two main avenues of approach.[1] One of these, the western access, runs along Route 9 from the Laotian border, through the village of Lang Vei to Khe Sanh. The other is a small valley to the northwest, formed by the Rao Quan River, which runs between Dong Tri Mountain and Hill 861. (See Map 3). Another key terrain feature is Hill 558 which is located squarely in the center of the northwestern approach. The only stumbling block to the NVA in early 1967 was a handful of Marines, U. S. Army Special Forces advisors, and South Vietnamese irregulars.(6) (See Map 3). The "Green Berets" were the first American troops in the area when, in August 1962, they established a Civilian Irregular Defense Group (CIDG) at the same site which later became the Khe Sanh Combat Base (KSCB). The first Marine unit of any size to visit the area was the 1st Battalion, 1st Marines (1/1) which, in April 1966, was participating in Operation VIRGINIA. In early October 1966, the 1st Battalion, 3d Marines, which was taking part in Operation PRAIRIE, moved into the base and the CIDG camp was relocated near Lang Vei, 9,000 meters to the southwest where it continued surveillance and counterinfiltration operations. The battalion remained at Khe Sanh with no significant contacts until February 1967 when it was replaced by a single company, E/2/9.[2] In mid-March 1967, Company E became engaged in a heavy action near Hill 861 and Company B, 1/9 moved in to reinforce. After a successful conclusion of the operation, E/2/9 returned to Phu Bai, and B/1/9 remained as the resident defense company. [Illustration: MAP 3 K.W. White