Operation Union II was a military operation that took place in the Vietnam War. It was a search and destroy mission in the Que Son Valley carried out by the 5th Marine Regiment. Launched on May 26, 1967 the operation ended June 5. The North Vietnamese Army (known to the U.S. Army as the NVA but properly the People's Army of Vietnam or PAVN) lost 701 killed and 23 captured, while U.S. casualties were 110 killed and 241 wounded.
The Que Son Valley is located along the border of Quang Nam and Quang Tin provinces. During the Vietnam War it lay in the southern part of South Vietnam's I Corps Military Region.
Populous and rice-rich, the valley was viewed as one of the keys to controlling South Vietnam's five northern provinces by the communists and by early 1967 at least two regiments of the 2nd Division of the People’s Army of Vietnam had been infiltrated into the area. The Que Son Valley was also recognized as strategically important by the U.S. Military Assistance Command, Vietnam (MACV). The 1st Battalion, 5th Marines (1/5) and 3rd Battalion, 5th Marines (3/5), experienced units that had fought in Vietnam since their arrival in the summer of 1966, were assigned to the valley in 1967 to support the outnumbered the South Vietnamese Army (ARVN) forces in the area.
During Operation Union, April 21 to May 16, the 3rd Battalion, 1st Marines had fought the PAVN 21st Regiment near the Marine outpost on Loc Son Mountain for control of the southern part of the Que Son Valley.
Operation Union II was launched on May 26 to destroy the withdrawing remnants of the PAVN with a helicopter assault by the U.S. 5th Marine Regiment, commanded by Colonel Kenneth Houghton. The assault was coordinated with ground attacks by the 6th ARVN Regiment and the 1st ARVN Ranger Group.
The plan called for 1/5, commanded by Lieutenant Colonel Hilgartner, to establish blocking positions in the western portion of the valley while the 3/5, commanded by Lieutenant Colonel Esslinger, was t...