Operations throughout the month of December 1968 consisted generally of boats coming upon groups of Viet Cong on the beach or crossing the river and being engaged by the boats. The enemy at this time did not recognize the maneuverability of the PBR or the heavy firepower of the river assualt craft and in most cases engaged without hesitation or prior planning. They were engaged and driven back with casualties far exceeding those of the U.S. Naval Forces. BM2 LEHMAN, USN, was the first person killed in Operation GIANT SLINGSHOT. On the afternoon of 14 December 1968, two PBRs from River Division 534 had spotted artillery onto several bunkers about twelve kilometers north of Tra Cu and were departing the area to resume patrol when they were ambushed and taken under intense rocket and machine gun fire at XT 405160. Both boats were hit. A Navy light helicopter fire team (LHFT) and one from the Army scrambled to the scene and placed strikes into the area. Six U.S. Navy personnel were wounded including Lehman, who later died of wounds.

Activity continued heavy throughout the month of December, and cache discoveries became more numerous during the latter half of the month.

Mid-December saw the arrival of the River LST USS HARNETT COUNTY (LST-821) at Ben Luc on the Vam Co Dong. Two more River Patrol Divisions were added bringing the total to five. LCDR Arthur J. ELLIOT, USN, was embarked in USS HARNETT COUNTY and assumed Vam Co Dong On-Scene Commander. On 15 December 1968 three separate rocket sites were discovered by the U.S. Army, all aimed at YRBM-18. On two hours notice YRBM-18 commandeered a passing Filipino tug and relocated downriver in the Vam Co River in the vicinity of the "French Fort" (XS 897616). USS HARNETT COUNTY was also pulled back and all three support craft stayed in the French Fort area for the next few days. The USS HARNETT COUNTY sailed daily to Ben Luc and returned at night. This maneuver was evaluated as being more dangerous than staying at Ben Luc, since Ben Luc afforded the relative safety of the Ben Luc Bridge Defense Force which defends the vital bridge linking Saigon to points south or Route Four. At 231825H, USS HARNETT COUNTY was fired upon by five rockets (XS 700665) while transiting back to French Fort. The USS HARNETT COUNTY and accompanying units received no hits.

The month ended on a saddened note when LCDR ELLIOT was killed instantly by shrapnel from a B-40 rocket while on a patrol. He had been on patrol on the upper Vam Co Dong (XT 280335) and was killed when one of the two PBRs on patrol was taken under fire.