The 9th Division was reactivated on 1 February 1966, and arrived in South Vietnam on 16 December 1966 from Fort Riley, Kansas.
On deployment the division was assigned to the III Corps Tactical Zone of Vietnam where it commenced operations in Dinh Tuong and Long An Provinces (6 January-31 May 1967) in Operation Palm Beach.
Its area of operations was in the rivers and canals of the Mekong Delta from 1967 to 1972.
Operating deep within the Viet Cong (VC)–controlled Delta, the Division was charged with protecting the area and its population against VC insurgents and ensuring the success of the South Vietnamese government's pacification program.
Faced with unrelenting physical hardships, a tenacious enemy and the region's rugged terrain, the Division established strategies and quantifiable goals for completing their mission.

Division commanding generals were: Maj.
Gen. George S. Eckhardt (February 1966 - June 1967), Maj.
Gen. George G. O'Connor (June 1967 - February 1968), Maj.
Gen. Julian Ewell (February 1968 - April 1969), Maj.
Gen. Harris W. Hollis (April 1969 - August 1969)
The infantry units that served with the 9th Infantry Division were:
2d Battalion, 39th Infantry
3d Battalion, 39th Infantry
4th Battalion, 39th Infantry
2d Battalion, 47th Infantry (Mechanized)
3d Battalion, 47th Infantry (Riverine)
4th Battalion, 47th Infantry (Riverine)
2d Battalion, 60th Infantry
3d Battalion, 60th Infantry (Riverine)
5th Battalion, 60th Infantry (Mechanized Dec. 1966 – 12 September 1968; Infantry 13 September 1968 – October 1970)
6th Battalion, 31st Infantry
Other units included:
Company E, 50th Infantry (reflagged Co. E, 75th Inf (Ranger)), 2 December 1967 – Aug 1969
Company E, 75th Infantry, Oct 1969 – Oct 1970
3d Squadron, 5th Cavalry, Feb 1967 – Nov 1971
9th Aviation Battalion, Jan 1967 – Aug 1969
2d Battalion, 4th Artillery (105mm Howitzer), Jan 1967 – Oct 1970
1st Battalion, 11th Artillery (105mm Howitzer), Jan 1967 – Aug 1969
3d Battalion, 34th Artillery (105mm Howitzer)(Riverine), Dec 1966 – Jul 1969 (Riverine)
1st Battalion, 84th Artillery (155mm Howitzer/8-inch Howitzer), Feb 1967 – Aug 1969
15th Engineer Battalion, Oct 1966 – Aug 1969
571st Engineer Company, Oct 1969 – Oct 1970
9th Medical Battalion, 4 January 1967 – 18 August 1969
9th Signal Battalion, 19 December 1966 – 19 August 1969
9th Supply and Transport Battalion, 16 December 1966 – 23 August 1969
709th Maintenance Battalion, 26 January 1967 – 20 August 1969
9th Adjutant General Company, 30 December 1966 – 26 August 1969
9th Military Police Company, 19 December 1966 – 25 September 1969
335th Army Security Agency Company (a.k.a. "
335th Radio Research Unit"), 12 January 1967 – 5 April 1971
99th Support Battalion, 1 October 1969 – 12 October 1970
493 Military Intelligence Detachment, 3/9th Inf Div, 19 December 1966 - 20 August 1970
One of the experimental units serving with the division was the 39th Cavalry Platoon (Air Cushion Vehicle) which used three of the specially designed hovercraft to patrol marshy terrain like the Plain of Reeds along the south Vietnamese/Cambodian border.
Other experimental units were the 1st and 2nd Airboat Platoons, which operated Hurricane Aircat airboats.

From 1967 on, one of the division's brigades (the 2d Brigade) was the Army contingent of the Mobile Riverine Force (MRF).
This brigade lived on the ships of Navy Task Force 117, and were transported on their infantry missions throughout the Mekong Delta on Tango boats (converted World War II landing craft) supported by various other armored boats.
The MRF was often anchored near the South Vietnamese city of Mỹ Tho, or near the Division's Đồng Tâm Base Camp and they conducted operations in coordination with the Navy SEAL teams, the South Vietnamese Marines, units of the ARVN 7th Division and River Assault Groups.
Following the Tet offensive in 1968, General Westmoreland stated that the Division and the MRF saved the Delta region from falling to the People's Army of Vietnam forces.
In 1969, the division also operated throughout IV Corps.

Chuck Hagel, former Secretary of Defense, served
The 9th Division was reactivated on 1 February 1966, and arrived in South Vietnam on 16 December 1966 from Fort Riley, Kansas. On deployment the division was assigned to the III Corps Tactical Zone of Vietnam where it commenced operations in Dinh Tuong and Long An Provinces (6 January-31 May 1967) in Operation Palm Beach. Its area of operations was in the rivers and canals of the Mekong Delta from 1967 to 1972. Operating deep within the Viet Cong (VC)–controlled Delta, the Division was charged with protecting the area and its population against VC insurgents and ensuring the success of the South Vietnamese government's pacification program. Faced with unrelenting physical hardships, a tenacious enemy and the region's rugged terrain, the Division established strategies and quantifiable goals for completing their mission.
Division commanding generals were: Maj. Gen. George S. Eckhardt (February 1966 - June 1967), Maj. Gen. George G. O'Connor (June 1967 - February 1968), Maj. Gen. Julian Ewell (February 1968 - April 1969), Maj. Gen. Harris W. Hollis (April 1969 - August 1969)
The infantry units that served with the 9th Infantry Division were:
2d Battalion, 39th Infantry
3d Battalion, 39th Infantry
4th Battalion, 39th Infantry
2d Battalion, 47th Infantry (Mechanized)
3d Battalion, 47th Infantry (Riverine)
4th Battalion, 47th Infantry (Riverine)
2d Battalion, 60th Infantry
3d Battalion, 60th Infantry (Riverine)
5th Battalion, 60th Infantry (Mechanized Dec. 1966 – 12 September 1968; Infantry 13 September 1968 – October 1970)
6th Battalion, 31st Infantry
Other units included:
Company E, 50th Infantry (reflagged Co. E, 75th Inf (Ranger)), 2 December 1967 – Aug 1969
Company E, 75th Infantry, Oct 1969 – Oct 1970
3d Squadron, 5th Cavalry, Feb 1967 – Nov 1971
9th Aviation Battalion, Jan 1967 – Aug 1969
2d Battalion, 4th Artillery (105mm Howitzer), Jan 1967 – Oct 1970
1st Battalion, 11th Artillery (105mm Howitzer), Jan 1967 – Aug 1969
3d Battalion, 34th Artillery (105mm Howitzer)(Riverine), Dec 1966 – Jul 1969 (Riverine)
1st Battalion, 84th Artillery (155mm Howitzer/8-inch Howitzer), Feb 1967 – Aug 1969
15th Engineer Battalion, Oct 1966 – Aug 1969
571st Engineer Company, Oct 1969 – Oct 1970
9th Medical Battalion, 4 January 1967 – 18 August 1969
9th Signal Battalion, 19 December 1966 – 19 August 1969
9th Supply and Transport Battalion, 16 December 1966 – 23 August 1969
709th Maintenance Battalion, 26 January 1967 – 20 August 1969
9th Adjutant General Company, 30 December 1966 – 26 August 1969
9th Military Police Company, 19 December 1966 – 25 September 1969
335th Army Security Agency Company (a.k.a. "335th Radio Research Unit"), 12 January 1967 – 5 April 1971
99th Support Battalion, 1 October 1969 – 12 October 1970
493 Military Intelligence Detachment, 3/9th Inf Div, 19 December 1966 - 20 August 1970
One of the experimental units serving with the division was the 39th Cavalry Platoon (Air Cushion Vehicle) which used three of the specially designed hovercraft to patrol marshy terrain like the Plain of Reeds along the south Vietnamese/Cambodian border. Other experimental units were the 1st and 2nd Airboat Platoons, which operated Hurricane Aircat airboats.
From 1967 on, one of the division's brigades (the 2d Brigade) was the Army contingent of the Mobile Riverine Force (MRF). This brigade lived on the ships of Navy Task Force 117, and were transported on their infantry missions throughout the Mekong Delta on Tango boats (converted World War II landing craft) supported by various other armored boats. The MRF was often anchored near the South Vietnamese city of Mỹ Tho, or near the Division's Đồng Tâm Base Camp and they conducted operations in coordination with the Navy SEAL teams, the South Vietnamese Marines, units of the ARVN 7th Division and River Assault Groups. Following the Tet offensive in 1968, General Westmoreland stated that the Division and the MRF saved the Delta region from falling to the People's Army of Vietnam forces. In 1969, the division also operated throughout IV Corps.
Chuck Hagel, former Secretary of Defense, served 
9th Infantry Division (United States)