Includes over 50 maps and illustrations This monograph forms part of the Indochina Monograph series written by senior military personnel from the former Army of the Republic of Vietnam who served against the northern communist invasion. “For several years Cambodia, under the leadership of Prince Norodom Sihanouk, had condoned the use of part of its territory by the Vietnamese Communists for infiltration routes and logistic bases. These bases supported enemy activities in South Vietnam’s Military Regions 3 and 4 and a significant part of Military Region 2 but were protected because of Cambodia’s declared neutrality. However, the change in government on 18 March 1970 provided South Vietnam and the United States the opportunity to neutralize and disrupt much of the enemy logistic system across the border. Sanctioned by the new Cambodian government and approved by the Presidents of the Republic of Vietnam and the United States, South Vietnamese and U.S. forces launched combined operations into Cambodia’s border area from 30 April to 30 June 1970. As the Assistant Chief of Staff J3 of the Joint General Staff, RVNAF, I participated in the combined planning for these historic operations with military representatives from Cambodia and the United States and then monitored the operations constantly for the Chairman JGS. In conducting my analysis I have relied on my personal involvement and observations as J3 and interviews with former members of the Republic of Vietnam Armed Forces.” -Author’s Introduction.