Operation Lam Son 719 was a crucial test of Vietnamization that began on 8 February 1971. The United States provided air and artillery support for 16,000 elite troops from Army of the Republic of Vietnam (ARVN) who crossed the border into Laos and raided the Ho Chi Minh Trail. Bad weather, command bungling, and North Vietnamese Army (NVA) counterattacks led to heavy losses on the withdrawal. There were more than 8,000 ARVN casualties and 1,462 U.S. casualties, and more than 100 helicopters and 150 tanks were left behind. ARVN morale was so devastated that observers doubted South Vietnam could defend itself.
taken from - Stanley I. Kutler, ed., Encyclopedia of the Vietnam War (New York: Simon & Schuster Macmillan, 1996), 276.