At the same time 1/13 worked over the assault force, the FSCC put a secondary box into effect for the benefit of the back-up units. The Army 175mm batteries were responsible for two sides which were about 500 meters outside the primary box. On order, the gunners rolled their barrages in toward the sides of the primary box and back out again. The third side was sealed by continuous flights of aircraft under the control of the TPQ-10 radar. Whenever B-52s could be diverted in time, Arc Light strikes were used to saturate the approach routes to the battle area.[(157)]
Another key factor in the defense of Khe Sanh was the manner in which Lieutenant Colonel Hennelly's FSCC coordinated their air effort with the artillery so that the two components were complimentary. One prime example was the Mini-Arc Light which was devised by the Assistant Fire Support Coordinator, Captain Kenneth O. W. Steen and the TIO, Captain Baig. As the name implies, this technique was used against an area target the same as a B-52 strike, only the former could be organized and employed much quicker. When intelligence reports indicated that NVA units were in a certain region, the FSCC plotted a 500 by 1,000-meter block in the center of the suspected area or across a likely route of march. Two A-6 Intruders, each armed with 28 500-pound bombs, were called on station for a TPQ and the batteries at Khe Sanh, Camp Carroll, and the Rockpile were alerted for a fire mission. Thirty seconds before the two A-6s dropped, the 175mm batteries, concentrating their fire on one half of the block, salvoed the first of approximately 60 rounds. At the same time the A-6s rippled their load down the middle of the block, the 1/13 batteries opened up on the second half with around 200 155mm, 105mm, and 4.2-inch rounds. The trajectory and flight time of all ordnance were computed so that the bombs and initial artillery shells hit at the same instant. The saturation of the target area was such that any enemy soldiers caught in the zone during the bombardment simply ceased to exist.[(158)]
During the second week in February, a special Mini-Arc Light was directed against a major NVA headquarters. Two members of the 26th Marines S-2, Majors Robert B. Coolidge and Jerry E. Hudson, learned from their various sources that a force-wide meeting of NVA commanders and their staffs would occur in an abandoned schoolhouse near the Laotian border. A beefed-up Mini was prepared to welcome the delegates. For this strike, the target block was reduced to 500 by 300 meters around the schoolhouse which would take in, as one of the planners stated, "the hangers-on and other idlers who usually congregate around large staffs." Twenty minutes after the meeting was scheduled to start, the trap was sprung. Two Marine A-6 Intruders and four F-4B Phantoms unloaded 152 500-pound bombs into the block in concert with the opening volleys of eight artillery batteries (total of 350 artillery rounds).[(159)] The target was obliterated, but whether or not this unusual ambush netted any NVA brass-hats was never ascertained.
The Micro-Arc Light was executed in the same manner as the Mini except smaller amounts of ordnance were used and the block was cut down to 500 by 500 meters. Any aircraft on station would suffice, preferably ones armed with 12 to 16 500-pounders. Artillery fire was reduced to 30 rounds from the 175mm guns and 100 mixed rounds from Lieutenant Colonel Hennelly's battalion. The advantage of the Micro was that it could be put into effect within 10 minutes while it took roughly 45 minutes to plan and execute the Mini. On an average night, three to four Minis and six to eight Micros were executed, usually to the south and southeast of the base; both were extremely effective.[(160)]
The massive firepower supporting the Marines would have been almost useless had they not known where and when to employ it. The 26th Marines intelligence section was responsible for this facet of the operation and these people had more than a passing knowledge of the enemy's past strategy. At Dien Bien Phu and Con Thien, the Communists had followed a fairly predictable pattern--not unlike the classic siege of the 18th Century. There were three distinct phases involved in this type of campaign: arrival on the scene and encirclement of the garrison, construction of siege works and support facilities, T-ing the sapheads and final assault. After investing the base, the North Vietnamese first established numerous forward logistic bases within a few thousand meters of the base. Under the cover of darkness, the enemy soldiers dug a series of shallow trenches, interlaced with supply bunkers, leading from these points toward the American positions. The first trenches began to appear at Khe Sanh around 23 February and the heaviest concentration was to the south and southeast. Once in close, the main trenches branched off into ones which paralleled the Marines lines; these secondary trenches, which from the air looked like long fingers reaching greedily toward the base, were the ones from which the NVA assault troops intended to attack.[(161)]
At first, the defenders tried to prevent the enemy from moving in too close to the base. The routes into the valley were saturated; artillery H&I fire and frequent air strikes were employed but such tactics only tended to slow down the enemy and force him to bypass certain routes--they did not stop him. Constant, massed artillery would have effectively blocked infiltration but that alternative was, from a logistics standpoint, impossible. The S-2 personnel recommended that the best way to counter the enemy was to allow the North Vietnamese to close and pursue their siege tactics and then, to borrow a phrase used by General "Chesty" Puller (then a colonel) on 28 November 1950 when his regiment was surrounded near the Chosin Reservoir in Korea, "that simplifies our problem of finding these people and killing them."[(162)]
The S-2 section utilized a multitude of sources to develop an accurate picture of the enemy's activity around the base. While much of this information was self-generated, the 26th Marines received substantial intelligence support from the MACV, III MAF, and 3d Marine Division Headquarters. Ground and aerial observers, photo reconnaissance, infrared imagery, target lists of higher headquarters, crater analysis, shell/flash reports, and agent reports were all tools of the intelligence community at Khe Sanh. By comparing this information with the knowledge of enemy doctrine as applied in past situations, the S-2 staff was able to accurately estimate the intentions of the NVA on a day-to-day basis.
One good example of how this intelligence produced hard results occurred in late February. From their various inputs, the two men who were responsible for the earlier attack on the NVA staff conference, Majors Coolidge and Hudson, pinpointed the exact location of 12 artillery positions and 2 major ammunition depots. These targets were concentrated in two main areas to the south of the base. Air strikes were called in on the enemy positions and, after the planes departed, the whole area erupted in secondary explosions which lasted for the next 40 minutes. Two weeks later, these officers repeated a similar performance in another area.[(163)]
The activities of the intelligence community at Khe Sanh and higher headquarters were vital to the conduct of the battle. Almost every major attack against the 26th Marines was picked up well in advance by the S-2 section. Whenever enemy activity was detected, the information was passed to the FSCC and this was the signal for Colonel Lownds to put his defensive fire plan into effect. The base was placed on Red Alert, the primary and secondary boxes fired, and saturation air strikes were employed. This method of cutting off the attack force by massed fires, once the S-2 section had provided a warning, proved to be a decisive factor in thwarting the major enemy thrusts which came late in February.[(164)]