Any offensive planning by the U.S. was, however, limited by the passage on 29 December 1970 of the Cooper-Church Amendment, which prohibited U.S. ground forces and advisors from entering Laos. "Dewey Canyon II" would, therefore, be conducted within territorial South Vietnam in order to reopen Route 9 all the way to the old Khe Sanh Combat Base, which had been abandoned by U.S. forces in 1968. The base would be reopened and would then serve as the logistical hub and airhead of the ARVN incursion. U.S. combat engineers were tasked with clearing Route 9 and rehabilitating Khe Sanh while infantry and mechanized units secured a line of communications along the length of the road. U.S. artillery units would support the ARVN effort within Laos from the South Vietnamese side of the border while Army logisticians coordinated the entire supply effort for the South Vietnamese. Air support for the incursion would be provided by the aircraft of the United States Air Force (USAF), Navy and Marine Corps and U.S. Army aviation units were tasked with providing complete helicopter support for the ARVN.