Department of Defense (USMC) Photo A801114
Rangers occupy a defensive trench east of the runway and actually just
outside the inain base. The American command wanted a Vietnamese unit
to participate in Khe Sanh for "psychological" reasons as well as military.
mander, provide South Vietnamese units to participate in the defense of the combat base, citing "psychological reasons as well as military." Lam agreed, and on 27 January, Captain Hoang Pho and his ARVN 37th Ranger Battalion arrived at the combat base and took their place at the east end of the runway just forward ot Company B, 1st Battalion, 26rh Marines, actually outside of the base defensive perimeter. According to one source. Colonel Lownds wanted "to gain more elbow room ... to push out the perimeter" since he had received implied criticism from his superiors about the limited extent of his defenses in this sector.39 Although their unit, 318 men strong, was about 100 short of its authorization, these tough, disciplined soldiers would prove themselves time and again during the battle, earning the respect of the Marines.40
Enemy sappers were at work, apparently preparing the way for planned ground attacks. Marines on the perimeter found barbed wire cut, but replaced to look as if it were whole, and Claymore mines* turned around to face Marine trenches.41 Intelligence reports from higher headquarters warned Colonel Lownds to be watchful for signs of NVA tunneling. The Marines monitored seismic intrusion detectors, drove metal engineer stakes into the ground and listened to them with stethoscopes borrowed from the medical unit, and even employed divining rods. They dug a number of "countermines" in response to possible indications of tunneling, but found no enemy tunnels.42
Beyond Marine positions, American aircraft opened a new era in warfare,
planting unattended ground sensors near likely enemy avenues of approach
and assembly areas.** These devices were extremely sensitive and could
monitor sound or vibrations, transmitting their information by radio
to intelligence personnel. The position of each sensor was carefully
recorded, permitting the Marines to quantify unusual enemy activity.
By noting the activation ot a number of different sensors, intelligence
personnel could estimate the size and composition of an enemy unit,
as well as its direction of march and speed. The devices would play
a key role in the battle.43***
By the end of January, intelligence officers painted a frightening picture ot the magnitude of the North Vietnamese effort around Khe Sanh. Reacting to developments. Major General Rathvon McC. Tompkins, the commanding general of the 3d Marine Division, ordered Lownds to limit patrolling to within 500 meters of friendly lines. Tompkins feared that the North Vietnamese wanted to draw the Marines out into the open, away from the protection ot their bunkers, trenches, mines, and barbed wire. Patrolling, he reasoned, was unnecessary because intelligence was
* A directional anti-personnel mine emplaced above ground facing the
** According to Colonel Dabney, he observed that these sensors were planted "by black, unmarked, 'Air America' [a CIA sponsored aviation company] birds which looked to me to be B-26s." Dabney Comments.
*** Colonel John F. Mitchell, who in 1968 commanded the 1st Battalion,
9th Marines at Khe Sanh, commented that the 26th Marines provided him
in early February with a "black box" that monitored sensors along Route
9. He observed that "it was very productive." His battalion S-2 or intelligence
officer listened in on the NVA radio nets in conjunction with the sensor
monitoring and "the raw intelligence gleamed . . . was put to good use
throughout the siege." Mitchell Comments.