For some time, the American forces had been aware that the PAVN/VC was about to launch some type of major offensive. Westmoreland was convinced that this big push would come either just before or right after Tết, but not during the holidays and probably at Khe Sanh and in the Vietnamese Demilitarized Zone sector. At Da Nang, III MAF knew that the PAVN/VC were on the move. Marine and Army reconnaissance flights using infrared technology and XM-3 "People Sniffer" airborne personnel detectors (APD) mounted on UH-1 helicopters indicated strong enemy concentrations in the hills near Hieu Duc west of the 7th Marines. Lieutenant Colonel William J . Davis, the commanding officer of the 1/7 Marines, recalled that his unit began to take fewer casualties from surprise firing devices or boobytraps and began to suspect that enemy troops unfamiliar with the terrain might be attempting to move into his sector. Davis notified the division headquarters of his findings. According to Davis, a few hours later, Robertson called a division briefing for all battalion commanders. At the briefing, the division G-2 or intelligence officer, told the assembled officers that "they are finally going to come out and fight. We don't know why, but we know they are!" He later confided to Davis, "Bill, your phone call was right on the money! I called all the regiments and battalions and the same was happening to them."