The first major battle of Operation Lam Son 720 takes place as North Vietnamese forces hit the same South Vietnamese 500-man marine battalion twice in one day. Each time, the communists were pushed back after heavy fighting. Earlier, the South Vietnamese reportedly destroyed a North Vietnamese base camp and arms production facility in the A Shau Valley. On May 19, in a six-hour battle, South Vietnamese troops engaged the communists. Three Allied helicopters and a reconnaissance plane were downed by enemy ground fire. The fighting, air strikes, and artillery fire continued in the A Shau Valley through May 23; the South Vietnamese claimed the capture of more communist bunker networks and the destruction of large amounts of supplies and ammunition.