Which South Vietnamese operation invaded Laos in 1971 with US air support?

Operation Lam Son 719 was the South Vietnamese operation that invaded Laos in 1971 with US air support. It began on February 8, 1971, as an Army of the Republic of Vietnam (ARVN) offensive into southeastern Laos.

The target was the Ho Chi Minh Trail, the North Vietnamese logistical network that moved troops and supplies toward South Vietnam. ARVN forces advanced west along Route 9 toward Tchepone, a major logistical center. The operation was designed partly to test Vietnamization—the US policy of transferring more combat responsibility to South Vietnamese forces while American troops withdrew.

US ground troops were barred from entering Laos, but American aircraft, helicopters, artillery, logistics, and advisers supported the incursion. North Vietnamese forces responded with armor, heavy artillery, infantry, and strong anti-aircraft defenses. Although ARVN troops briefly reached Tchepone, they withdrew by March 25 after suffering heavy losses.

The operation is often confused with earlier US campaigns such as Cedar Falls or Junction City, which took place in South Vietnam. Lam Son 719 is specifically associated with the 1971 cross-border attack into Laos and the Vietnamization era.