In September 1967 the NVA started their major shelling. 152mm howitzers, 120mm and 82mm mortars and 122mm rockets hit the base daily. During the climax of the attack (September 19 - 27, 1967) over three thousand rounds of artillery pounded the fire base. On September 25, a reported 1200 rounds pounded the hill sides of the 158m mound of red dirt.
On 14 October 1967 21 Marines from 2nd Battalion 4th Marines were killed defending the C-2 Bridge on Route 561.
The Marine Corps rotated battalions in and out of Con Thien every thirty days. The constant shelling and the threat of an NVA assault took a psychological toll on the Marines, the base was nicknamed "Our Turn in the Barrel" and "the Meat Grinder", while the DMZ was said to stand for "Dead Marine Zone."
More than 1400 Marines were killed and nearly 9300 wounded in the fighting in and around Con Thien. NVA losses were put at nearly 9600 killed in action and over 160 prisoners of war.
Con Thien was in the news during the time it was under artillery attack. TIME featured the story on the cover of its 6 October 1967, issue which was instrumental in bringing the reality of Vietnam combat to American readers. David Douglas Duncan's photos of the Marines at Con Thien were featured in the 27 October 1967 issue of Life Magazine and in his book War Without Heroes.
2nd Battalion, 1st Marines took over the defense of Con Thien in mid-December. During the Christmas truce period the Battalion added 11 bunkers and dug a new trench along the forward slope. The troops then sandbagged existing bunkers with a "burster layer" in the roofs, usually consisting of airfield matting to burst delayed fuse rounds, they then covered the positions with rubberized tarps to keep the water out. By the end of the year, all of the new bunkers had been sandbagged and wired in with the new razor wire. During January the NVA kept up sporadic fire on the base firing for 22 of 31 days with each barrage averaging about 30 rounds. The artillery fire gradually destroyed the minefield and bunkers protecting the northwest of the base causing regular casualties.