1971 in the Vietnam War

February
The Battle of Ban Dong was a major battle of the Vietnam War that took place in Laos, involving the North and South Vietnamese armies. The battle lasted from February 8 to March 20, 1971. Operation Lam Son 719 (Chiến dịch Lam Sơn 719 or Chiến dịch đường 9 – Nam Lào) was a limited-objective offensive campaign conducted in southeastern portion of the Kingdom of Laos by the armed forces of the Republic of Vietnam (South Vietnam). The objective of the campaign was the disruption of a possible future offensive by the People's Army of Vietnam (PAVN), whose logistical system within Laos was known as the Ho Chi Minh Trail (the Truong Son Road to North Vietnam).
 * February 8 – March 20, 1971
 * February 8 - March 25, 1971

March
The SS Columbia Eagle incident refers to a mutiny that occurred aboard the merchant vessel Columbia Eagle in March 1970 when crewmembers seized the vessel and sailed to Cambodia.

May
Operation Ranch Hand was a U.S. Military operation during part of the Vietnam War, it started in 1962 and lasted till May 1971. It involved spraying an estimated 12 million + US gallons of defoliants over rural areas of South Vietnam in an attempt to deprive the Viet Cong of vegetation cover and food.
 * May

August
Operation Chenla II was a major military operation conducted by the Cambodian military (then known as FANK) during the Cambodian Civil War.
 * August 20 - December 3, 1971