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the tenuous supply route to Ca Lu. Since November 1967, Colonel Joseph
E. Lo Prete's 3d Marines had conducted Operation Lancaster protecting
the western flank of the 9th Marines in Kentucky. The Lancaster area
of operations contained the key Marine bases of Camp Carroll, an important
artillery position, the Rockpile, and Ca Lu. The Rockpile, a 700-foot
sheer cliff outcropping, dominated the nearby terrain. Perched on its
top, Marine observers had a clear view of the most likely approaches
into the Cam Lo River Valley and of Route 9, the two most strategic
east-west arteries in the DMZ sector. About 12,000 meters below the
Rockpile and pan of the Dyemarker system was Ca Lu, in effect the southern
terminal of Route 9 since the North Vietnamese had effectively cut the
road between Ca Lu and Khe Sanh, about 20,000 meters to the west. An
obvious way station for any relief effort of Khe Sanh, Ca Lu, at the
junction of the Quang Tri River and Route 9, also provided the Marines
an outpost to warn of enemy infiltration into the Lancaster area from
the west, southwest, and from the Ba Long Valley to the southeast. Similar
to much of the terrain in the DMZ area, the Lancaster area of operations
consisted of rolling hills rising into jungle-covered mountains of 700-800
feet with tree canopies reaching up to heights of 20 to 60 feet. Fifteen-foot
elephant grass and dense brush vegetation restricted movement even in
the relatively low regions.

Like Colonel Smith and the 9th Marines, Colonel Lo Prete was tied to his base areas. With only two infantry battalions, and one of those battalions having only two companies, the 3d Marines commander had to make do with limited resources and manpower. Lo Prete maintained his command post at Camp Carroll which was also the home for Lieutenant Colonel William M. Cryan's 2d Battalion, 9th Marines. Cryan with only his Companies E and H under his operational control kept Company H at Carroll and positioned Company E about 3,000 meters southeast of Camp Carroll where it protected a main supply route. Lo Prete assigned his other battalion. Lieutenant Colonel Gorton C. Cook's 3d Battalion, 9th Marines, the responsibility for the defense of both Ca Lu and the Rockpile area. Cook and three of his companies remained in the Thon Son Lam sector just below the Rockpile while he placed his Company L at Ca Lu. An article in the battalion newsletter at the time noted that the sector was "pretty quiet now except for some sporadic ambushes between here and our company-sized outpost at Ca Lu."78

Artillery and tanks reinforced the infantry in Lancaster. Three 105mm
howitzer batteries and one 155mm howitzer battery all under the 1st
Battalion, 12th Marines at Carroll provided direct support to the infantry
battalions. An ad hoc battery of mixed caliber guns, Battery W, 1st
Battalion, 12th Marines, was with Company L at Ca Lu. Company B, 3d
Tank Battalion maintained two platoons of M48 medium gun tanks and one
heavy section of M67A2 flame tanks at Carroll. For the most part, the
tanks bolstered the defenses at Camp Carroll and furnished protection
for road convoys to Ca Lu. An attached U.S. Army artillery unit. Battery
C, 1st Battalion, 44th Artillery (Automatic Weapons, Self Propelled)
also augmented the Marine fire power. The Army M42s or "dusters" armed
with twin 40mm antiaircraft guns employed as machine guns gave added
protection to Marine convoys and to the Marine fixed defenses.79

The Marines worried most about their relatively exposed position at Ca Lu. There, the isolated garrison numbered about 625 Army, Navy, and Marine personnel including the Marine infantry company. Navy Seabees and Marine engineers had nearly completed the permanent facilities required for the Dyemarker project. While not directly attacking the Marine outpost, the North Vietnamese had mined Route 9 occasionally in December and ambushed one Marine convoy on a return trip from Ca Lu to the Rockpile. Despite a relative lull during the first two weeks of January, Marine intelligence indicated that North Vietnamese forces were on the move.80

A division "Stingray" reconnaissance team operating in the general area of the Ca Lu base soon confirmed the presence of enemy troops in the general area.* On 12 January, about l4l5 in the afternoon, Reconnaissance Team 2C3, using the codename "Blue Plate" and operating in the mountains about 4,000 meters southwest of Ca Lu below the Quang Tri River, radioed back that it was being followed by five NVA "wearing black pjs and carrying automatic weapons." The "Blue Plate" Marines fired upon the enemy but missed. For a time all was quiet and the Marines continued upon their way. About two hours later, the Marines came back on the air to report that they were surrounded by about 30 North Vietnamese troops armed with AK-47s. Marine gunships appeared overhead and provided covering fire while

* Stingray patrols usually consisted of a small Marine reconnaissance unit, usually squad-size, which called artillery and air on targets of opportunity.

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