Operation Phiboonpol (9–11 June 1971) was a "short but very intense engagement" of the Laotian Civil War. Five Royal Lao Government battalions went on the offensive in Military Region 4 of the Kingdom of Laos to try to regain the Boloven Plateau, which overlooked the vital Ho Chi Minh Trail lying to its east. Stopped in its tracks by the People's Army of Vietnam, with its first use of tanks in southern Laos, the Royalists held firm while close air support inflicted heavy casualties on North Vietnamese attackers. A Thai mercenary company sent as a Royalist relief force was ambushed and wiped out. For weeks after the battle, vultures feasted on unburied corpses.