The U.S. 9th Marine Regiment and the 3rd Brigade of the 101st Airborne Division, along with South Vietnamese forces, commence Operation Apache Snow in the A Shau Valley in western Thua Thien Province. The purpose of the operation was to cut off the North Vietnamese and prevent them from mounting an attack on the coastal provinces.
The operation began with a heliborne assault along the Laotian border and then a sweep back to the east. First contact with the enemy was made by a rifle company from the 101st Airborne on the slopes of Hill 937, known to the Vietnamese as Ap Bia Mountain. Entrenched in prepared fighting positions, the North Vietnamese 29th Regiment repulsed the initial American assault and on May 14 beat back another attempt by the 3rd Battalion, 187th Infantry. An intense battle raged for the next 10 days and the mountain came under heavy Allied air strikes, artillery barrages, and 10 infantry assaults. On May 20, Maj. Gen. Melvin Zais, commanding general of the 101st, sent in two additional U.S. airborne battalions and a South Vietnamese battalion as reinforcements. The communist stronghold was finally captured in the 11th attack, when the American and South Vietnamese soldiers fought their way up to the summit of the mountain. In the face of the four-battalion attack, the North Vietnamese retreated to sanctuary areas in Laos.
During the intense fighting, 597 North Vietnamese were reported killed and U.S. casualties were 56 killed and 420 wounded. Due to the bitter fighting and the high loss of life, the battle for Ap Bia Mountain received widespread unfavorable publicity in the United States and American media dubbed it "Hamburger Hill," a name evidently derived from the fact that the battle turned into a "meat grinder." Since the operation was not intended to hold territory but rather to keep the North Vietnamese Army off-balance, the mountain was abandoned soon after the battle and occupied by the North Vietnamese a month later.
American public outrage over what appeared to be a senseless loss of American lives was exacerbated by publication in Life magazine of the pictures of the 241 U.S. soldiers killed the week of the Hamburger Hill battle. Gen. Creighton Abrams, commander of U.S. Military Assistance Command Vietnam, was ordered by the White House to avoid such battles. Because of Hamburger Hill, and other battles like it, the U.S. started to shift its policy towards Vietnamization, wherein primary responsibility for the fighting would be handed over to the South Vietnamese.