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feasibility and desirability of the employment of heavy artillery
units in forward firing positions for limited periods of time."26

About a month later, the 3d Marine Division artillery participated
in a combined arms "raid" to silence the enemy guns across the eastern
DMZ, especially in the Cap Mui Lay sector. Enemy gun emplacements in
and north of the DMZ posed a credible artillery threat to American and
South Vietnamese bases and positions in northeastern Quang Tri Province.
Although employing brief sporadic volleys rather than a continuous bombardment,
the North Vietnamese guns occasionally could disrupt U.S. operations
and logistic activities. At 1615 on 20 June, for example, North Vietnamese
gunners hit Dong Ha with six 152mm rounds which resulted in the destruction
of the ammunition supply point there. Secondary explosions and fires
continued throughout that night and the next day. In all, the enemy
artillery caused the loss of 10,500 tons of Marine ammunition, about
20 days worth of supply.27*

For more than a year. III MAF had undertaken several efforts to counter the enemy use of its relative sanctuary area in and north of the DMZ. Operations High-rise, Headshed, and Neutralize all involved variations of the same theme: air and artillery attacks on enemy firing positions in and north of the DMZ. These operations were frustrated by the enemy's formidable array of antiaircraft weapons north of the DMZ, which precluded both effective bombing and the air observation necessary for adjusting artillery fire and assessing its effects. In each of these operations, even concentrated efforts failed to produce any noticeable effect on the Communist gunners.

On 20 June, by coincidence, the same date of the enemy artillery attack
on Dong Ha, General Westmoreland approved an earlier III MAF proposal
for another major combined arms interdiction campaign against the DMZ
sanctuary area. Codenamed Operation Thor after the Norse god of thunder,
the plan called for a week-long supporting arms effort involving units
of III MAF, Seventh Fleet, and Seventh Air Force in a joint attack on
North Vietnamese artillery, air defense, and coastal batteries located
in the Cap Mui Lay sector. This sector included the area extending north
of the southern boundary of the DMZ about 15 kilometers to Cap Mui Lay
and inland about 25 kilometers. The objectives were twofold: to destroy
NVA antiaircraft and field and coastal artillery, and to facilitate
further surveillance and continued attacks on targets in and north of
the DMZ. The III MAF commander, Lieutenant General Cushman, hoped that
success in this operation would preempt any NVA preparations for an
autumn offensive, while at the same time ending the threat to forward
III MAF bases and lines of communication.28

The concept of operations included four phases. In Phase I, the first two days, B-52s and attack aircraft would conduct heavy airstrikes to cover artillery units displacing forward to positions near the DMZ. Phases II and III, together lasting five days, were to include integrated attacks by air, artillery, and naval gunfire, first on targets in the coastal area, then expanding to the entire Cap Mui Lay sector. The events scheduled for Phase IV emphasized accomplishment of Operation Thor's second objective: the continued attack of targets in and north of the DMZ. In this last phase, most artillery units would withdraw to participate in other operations while observers would maintain surveillance of the area, directing the attack of reemerging targets. Phase IV, planned as an open-ended evolution, would continue indefinitely.29

The staggering firepower available for Operation Thor was commensurate
with the magnitude of the task at hand. Thirteen batteries of artillery
would participate, including the three 155mm batteries of Major Billy
F. Stewart's 4th Battalion, 12th Marines, reinforced by Battery K, 4th
Battalion, 13th Marines and the 1st 8-inch Battery. While these units
temporarily came under the operational control of the U.S. Army's 108th
Field Artillery Group for Operation Thor, all other 3dMarine Division
artillery units stood ready to participate in the operation, if necessary.**
The Seventh Fleet provided two cruisers and six destroyers, as well
as 596 sorties of tactical air. The MACV planners allocated 861 Air
Force sorties, including 210 B-52 strikes. The 1st Marine Aircraft Wing
scheduled 540 sorties, including 65 photo reconnaissance and electronic
warfare missions to be flown by Lieutenant Colonel Eric B. Parker's
Marine Composite Reconnaissance Squadron (VMCJ) l, which would provide
surveillance of the DMZ throughout the operation. All III MAF units
participating in the operation were under the control of Brigadier General
Lawrence H. Caruthers, Jr., USA, who commanded Provisional

* See Chapter 3 for discussion of the enemy gun positions in Cap Mui

** On 26 June, Prov Corps transferred counter-battery responsibility
from the 12th Marines to the 108th Field Artillery Group. (12th Mar
ComdC, Jun68, p. 1-III-7.)

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