3d Battalion's activity was involved in road sweeps, keeping open the main lines of communication among Camp Carroll, Dong Ha, Quang Tri, Camp Evans and Phu Bai. By the end of January, the battalion had conducted over 300 mine sweeps, averaging nearly 38,456 meters per day.27
At Da Nang, Lieutenant Colonel Cassedy's 1st Battalion performed much the same engineering role for the 1st Marine Division. Here, the mine-clearing mission took on even more importance given the VC emphasis on surprise explosive devices or boobytraps. In fact, in January, the engineers suffered almost all of their casualties in accomplishing this mission, seven out of the eight killed and 15 out of the 18 wounded. Like the 3d Battalion in the north, the 1st Battalion was spread out in support of its division's various regiments. At the beginning of the month, Cassedy's headquarters, Company C, and Company B were at Da Nang in support of the 7th Marines and 5th Marines respectively. With the formation of Task Force X-Ray in mid-January, Company B joined the 5th Marines at Phu Bai. The 1st Battalion's Company A stayed with the 1st Marines throughout the month, first at Quang Tri, then at Phu Bai.28
The enemy Tet offensive at the end of January and through most of February would impact on the engineers as much as on any of the III MAF units. In the struggle for Hue, engineer detachments from both Companies A and B, 1st Engineer Battalion accompanied the Marine infantry in the retaking of the city. The engineers built a pontoon bridge to replace the destroyed An Cuu Bridge over the Phu Cam Canal so that much-needed supplies could flow again into the city. Together with the reinforcing Army engineers and Seabees, the Marine engineer battalions worked to reconstruct the blown bridges, culverts, and highway cuts along the main lines of communication in I Corps, especially along Highway 1, the main north-south artery. Finally, by 2 March 1968, Route 1 was open from Da Nang to Dong Ha.29
During the relief of Khe Sanh in Operation Pegasus, the Marine engineers again played a vital role. Beginning in mid-March, Lieutenant Colonel Perry's 11th Engineer Battalion, together with Seabees and Army engineers, began the building of Landing Zone Stud at Ca Lu, the jumping-off point for the 1st Air Cavalry Division. While the Air Cavalry leapfrogged towards Khe Sanh, the 1st Marines slogged forward along Route 9 with the 11th Engineers clearing the path for them. In the advance, the engineers constructed 11 bridges and made 18 culvert bypasses along the road.30
The engineers had as large a role in the abandonment of Khe Sanh as they had in its relief. Company A, 1st Engineer Battalion, which had accompanied the 1st Marines in the relief of Khe Sanh, reported that its most significant accomplishment was the closing of the base. Beginning on 18 June and ending in early July, the engineers destroyed or buried 95 bunkers and more than 2,770 meters of trenchline. Using over 2,100 pounds ofTNT, the engineers exploded unexpended ammunition and caved in the former Marine defenses. What equipment they could not carry out, they demolished or buried so that it could not be used against allied forces in the future.31
In the north after the enemy Tet and Mini-Tet offensives and the closing of Khe Sanh, both the 11th Engineer Battalion and the 3d Engineer Battalion took on new missions as the 3d Marine Division took the offensive. While the 11th Engineer Battalion still continued to have a limited responsibility for the barrier, the battalion confined most of this effort to some minor road and bunker construction.* For the most part, the 11th Engineers took on the task of establishing the permanent fire bases for the division. By July, it had transformed LZ Stud near Ca Lu into Fire Support Base Vandegrift. Given the emphasis of the new commander of the 3d Marine Division, Major General Raymond G. Davis, upon mobile helicopter tactics, the construction of permanent and semi-permanent fire support bases became the major responsibilities of both engineer battalions in the north. In a remarkably short time, employing explosives, helicopter-transportable bulldozers, and chain saws, the engineers denuded and flattened entire mountain tops and transformed them into fortified gun positions so that Marine artillery could keep the fast-moving infantry within supporting range.
In the Da Nang area, the 1st Engineer Battalion inaugurated in the spring a series of clearing operations in support of the 1st Marine Division. Beginning in April, the engineers in support of the 7th Marines in the western sector began Operation Woodpecker, "designed to eliminate known or potential enemy rocket launching and ambush sites." After clearing
*After the initial enemy offensives in January and February, almost all construction of the barrier ended for all practical purposes. Planning for the barrier and some limited construction continued, however, under the Codename Duel Blade. On 22 October 1968, General Abrams, now the MACV commander, ordered the halt of all planning and construction for the project. Before all work came to a stop, the engineers had implanted three sensor fields in the eastern portion of the DMZ, south of the Ben Hai River. See Chapter 22.