Westmoreland adopted a strategy of attrition against the Viet Cong and the North Vietnamese Army, attempting to drain them of manpower and supplies. He also made use of the United States' edge in artillery and air power, both in tactical confrontations and in relentless strategic bombing of North Vietnam. Many of the battles in Vietnam were technically United States victories, with the United States Army in control of the field afterward; holding territory gained this way proved difficult, however. Public support for the war eventually diminished, especially after the Battle of Khe Sanh and the Tet Offensive in 1968. By the time he was re-assigned as Army Chief of Staff, United States military forces in Vietnam had reached a peak of 535,000 personnel. Westmoreland's strategy was ultimately politically unsuccessful. Growing United States casualties and the draft undermined United States support for the war, while large-scale casualties among non-combatants weakened South Vietnamese support. This also failed to weaken North Vietnam's will to fight, and the Government of South Vietnam—a factor largely out of Westmoreland's control—never succeeded in establishing enough legitimacy to quell defections to the Viet Cong.