In late 1971, North Vietnam was terribly worried about the situation in South Vietnam. Although the political situation was well in hand with the peace movement in the US, the military situation was dire, even though the US troops were pulling out in great numbers. The war in the south was being waged almost exclusively by North Vietnamese regular troops, not the native South Vietnamese Viet Cong. The indigenous Viet Cong had all but been wiped out by failed spring offensives over the last several years, the most famous being the Tet Offensive of 1968. Vo Nguyan Giap, the head of the North Vietnamese military, gambled that since the Army of S Vietnam (ARVN) and the US defeated the insurgency, they were not prepared for a conventional attack. On 30 March 1972, virtually the entire People’s Republic of Vietnam Army, 200,000 North Vietnamese troops including 300 tanks swept into S Vietnam. However, Giap underestimated the ARVN, which by 1972 was relatively well trained and equipped, and the destructiveness of American firepower. By June the offensive had ended in failure. It had made some territorial gains but the PAVN had suffered horrendous casualties, over 100,000 and 250 tanks by their count.