During the Vietnam War, the Iron Triangle was a Vietcong and North Vietnamese military bastion in South Vietnam, located in the province of Binh Duong. Using a network of tunnels, the communists were resupplied from their sanctuary in the Cambodia jungle, through the Ho Chi Minh Trail. By 1965, there had been a sharp increase in guerrilla activity in the Iron Triangle as the Vietcong launched surprise attacks on US and South Vietnamese Army outposts and infrastructure. Between 1966 and 1967, the US forces would carry out three military operations against North Vietnamese and Vietcong units in the area (operations Cedar Falls, Attleboro, and Junction City). This massive commitment of forces, that included intense B-52 bombing, sensibly reduced the guerrilla activity in the Iron Triangle, but never completely annihilated the network system. The more effective weapon used in the area were the tunnel rats.