Originally part of the 4th Infantry Division stationed at Ft. Lewis, WA. The battalion departed Tacoma, WA, on September 22, 1966, bound for Vietnam. They arrived in Vietnam on October 9, 1966. Their first base camp was called "Bear Cat." In November 1966, the battalion was relocated to Dau Tieng, Tay Ninh Province, at the southern edge of the Michelin rubber plantation and not far from the Cambodian border.

The 3rd Battalion, 22nd Infantry was transferred to the control of the  25th Infantry Division, on August 1, 1967.

Some time was spent at Cu Chi and Tay Ninh in August 1967, the Battalion returned to Dau Tieng. In 1968, while  based out of Dau Tieng, The 3rd Battalion, operated near Soui Cut, Cui Chi, Hoc Mon, Saigon, and Boa Trai. They remained in those areas until August 1969, whereupon they moved to Tay Ninh.

From August 1969 to January 1970, they operated in Tay Ninh Province; From February 1970 to May 1970, in Thien Ngon. In May 1970, they took part in the invasion of Cambodia, then moved  back to Tay Ninh in July 1970. They operated in Dau Tieng, (August 1970); Tri Tam, (September 1970); Dau Tieng, (October to November 1970); Xuan Loc, (December 1970); and Xuan Loc/ Long Binh, (January 1971 to 20 April 1971). 

At the end of April, 1971, the Battalion ended it's gallant service in Vietnam and  returned to America and were stationed at Ft. Carson, CO. for a short time before being deactivated. The 3rd Battalion is deactivated, but "The Regulars" are always ready to serve.

The Battalion was awarded the following decorations during it's Vietnam service.

Presidential Unit Citation (Army), Streamer embroidered SUOI TRE, VIETNAM (3rd Battalion less Company C), 22nd Infantry cited; DA GO 59, 1968)

Valorous Unit Award, Streamer embroidered TAY NINH PROVINCE (3rdBattalion, 22nd Infantry cited; DA GO 42, 1969)

Vietnamese Cross of Gallantry with Palm, Streamer embroidered VIETNAM 1966-1967 (3rd Battalion, 22nd Infantry cited; DA GO 3, 1970, as amended by DA GO 48,1971 )

Vietnamese Cross of Gallantry with Palm, Streamer embroidered VIETNAM 1967-1968 (3rd Battalion, 22nd Infantry cited; DA GO 48, 1971)