From early to late 1967, the U.S. command in Saigon was perplexed by a series of actions initiated by the PAVN/VC in the border regions. On 24 April a U.S. Marine Corps patrol prematurely triggered a PAVN offensive aimed at taking Khe Sanh Combat Base, the western anchor of the Marines' defensive positions in Quảng Trị Province. For 49 days during early September and lasting into October, the PAVN began shelling the U.S. Marine outpost of Con Thien, just south of the Demilitarized Zone (DMZ). The intense shelling (100–150 rounds per day) prompted Westmoreland to launch Operation Neutralize, an intense aerial bombardment campaign of 4,000 sorties into and just north of the DMZ.