This campaign was from 1 Jul 1970 to 30 June 1971. Fighting continued in Cambodia during early February before and after South Vietnam began its U.S.-aided drive in Laos, Lam Son 719, the most significant operation during this campaign.
Lam Son 719 was conducted out of I Corps by Vietnamese troops with US fire and air support. Their object was to cut the Ho Chi Minh Trail and to destroy enemy bases at Techepone, Laos. The operation consisted of four phases. In Phases I, called Operation DEWEY CANYON II, the 1st Brigade, US 5th Infantry Division (Mechanized) occupied the Khe Sanh area and cleared Route No. 9 up to the Laotian border. In the meantime, the US 101st Airborne Division conducted diversionary operations in the A Shau Valley. The US 45th Engineer Group had the mission of repairing Route No. 9 up to the Laotian border. This lasted from 30 January to 7 February 1971. During Phase II US forces continued to provide fire support, helilift, and tactical and strategic air support for ARVN units. This phase was 8 February to March 1971. Phase III ran from March to 16 March 1971; Phase IV was the withdrawal phase.
Faced with mounting losses, Lt. Gen. Hoang Xuan Lam, the commander of the invasion forces, decided to cut short the operation and ordered a withdrawal.
Lam Son 719, though it was less than a signal success, forestalled a Communist offensive in the spring of 1971. Enemy units and replacements enroute south were diverted to the scene of the action.