In addition to his infantry units, the regimental commander had an impressive array of artillery and armor. Lieutenant Colonel John A. Hennelly's 1/13 provided direct support for the 26th Marines with one 4.2-inch mortar battery, three 105mm howitzer batteries, and one provisional 155mm howitzer battery (towed). The 175mm guns of the U. S. Army's 2d Battalion, 94th Artillery at Camp Carroll and the Rockpile were in general support. Five 90mm tanks from the 3d Tank Battalion, which had been moved to Khe Sanh before Route 9 was cut, were attached to the 26th Marines along with two Ontos platoons from the 3d Antitank Battalion.[14] These highly mobile tracked vehicles could be rapidly mustered at any threatened point so Colonel Lownds generally held his armor in the southwestern portion of the compound as a back-up for L/3/26 and FOB-3. All told, the Khe Sanh defenders could count on fire support from 46 artillery pieces of varied calibers, 5 90mm tank guns, and 92 single or Ontos-mounted 106mm recoilless rifles. With an estimated 15,000 to 20,000 North Vietnamese lurking in the surrounding hills, the Marines would need it all.(42) Ironically, the incidents which heralded the beginning of full-scale hostilities in 1968 occurred in the same general area as the encounter which touched off the heavy fighting in 1967. On 19 January 1968, the 3d Platoon, I/3/26 was patrolling along a ridgeline 700 meters southwest of Hill 881N where, two days before, a Marine reconnaissance team had been ambushed. The team leader and radioman were killed and, while the bodies had been recovered, the radio and a coded frequency card were missing. The 3d Platoon was scouring the ambush site for these items when it was taken under fire by an estimated 25 NVA troops. The Marines returned fire, then broke contact while friendly artillery plastered the enemy positions. [Illustration: Five M-48 tanks of the 3d Tank Battalion lent the weight of their 90mm guns to the defense of the combat base. (USMC Photo A190884)] [Illustration: Two Ontos platoons of the 3d Antitank Battalion were on hand at Khe Sanh. The Ontos sports six 106mm recoilless rifles with coaxially mounted .50 caliber spotting rifles. (USMC Photo A369169)]