 The USAF serial number was painted in red on the fin over a horizontal red stripe across the length of the fin.The B-52 effort was concentrated primarily against suspected Viet Cong targets in South Vietnam, but the Ho Chi Minh Trail and targets in Laos were also hit.During the relief of Khe Sanh, unbroken waves of six aircraft, attacking every three hours, dropped bombs as close as 900 feet from friendly lines.