The 40th Armor Regiment was an armored regiment of the United States Army until its deactivation in 1997. It was redesignated and reactivated in 2005 as the 40th Cavalry Regiment serving in the 4th Brigade Combat Team (Airborne), 25th Infantry Division.
Constituted as the 4th Armored Regiment on 13 January 1941, the unit was retitled the 40th Armored Regiment on 8 May 1941. The regiment was inactivated from 1 January through 2 March 1942, at which point it was again activated until 20 September 1943 when the regiment was broken up and its elements used to form smaller independent units including the 40th and 709th Tank Battalions.
On 15 October 1957, the 40th and 709th Tank Battalions, as well as Troop E, 87th Cavalry Reconnaissance Squadron, were combined to form the 40th Armor Regiment under the Combat Arms Regimental System. Thereafter, elements of the regiment served dispersed among various army commands worldwide.
Company A, 40th Armor Regiment was activated as 1st Medium Tank Battalion, 40th Armor Regiment on 15 October 1957 and redesignated Company A, 40th Armor Regiment on 16 December of the same year. Assigned to the 171st Infantry Brigade (U.S. Army Alaska) on 20 May 1963 and was inactivated on 21 September 1969.
1st Battalion, 40th Armor Regiment was activated in 1975 and was subordinated to the 5th Infantry Division until the battalion was inactivated in 1987. The battalion was again activated in January 1996 in California and again inactivated in September 1997.
Company B, 40th Armor Regiment was activated at Fort Sill, Oklahoma, on 24 October 1963. The unit inactivated in 1976.
2nd Medium Tank Battalion, 40th Armor was activated on 1 July 1957 and subordinated to the 7th Infantry Division in Korea. The unit inactivated on 1 July 1963. On 9 October 1963, the unit was redesignated Company B, 40th Armor.
3rd Medium Tank Battalion, 40th Armor Regiment was activated on 15 October 1957 and subordinated to the 1st Cavalry Division in Korea. The unit inactivated on 1 September 1963.
Company D, 40th Armor Regiment was formed on 15 October 1957 (as 4th Medium Tank Battalion) and redesignated Company D, 40th Armor Regiment on 16 December of the same year. The unit was subordinated to the 172nd Infantry Brigade (U.S. Army Alaska). Later expanded to 4th Battalion, 40th Armor Regiment from March 1976 until April 1984, and subordinated to 4th Infantry Division.
5th Medium Tank Battalion, 40th Armor Regiment was reconstituted on 15 October 1957, subordinated to the U.S. Sixth Army in California, and inactivated on 19 February 1962. Redesignated 5th Battalion, 40th Armor Regiment on 27 March 1963 and subordinated to the 63rd Infantry Division of the Army Reserve. The unit inactivated on 31 December 1965.
Company F, 40th Armor Regiment was originally reconstituted on 15 October 1957 as 6th Medium Tank Battalion, 40th Armor Regiment. The unit was redesignated Company F, 40th Armor on 2 May 1958 and assigned to the U.S. Army's Berlin Brigade from 1 September 1963 forward. Later expanded to 6th Battalion, 40th Armor Regiment from September 1990 until May 1992.
7th Medium Tank Battalion, 40th Armor Regiment was activated on 1 May 1959. Redesignated 7th Battalion, 40th Armor Regiment on 1 April 1963. Subordinated to the 63rd Infantry Division of the Army Reserve and inactivated on 31 December 1965.
8th Medium Tank Battalion, 40th Armor Regiment was formed on 15 October 1957 and assigned on 20 May 1959 to the 96th Infantry Division of the Army Reserve. On 15 February 1963, the unit was redesignated 8th Tank Battalion, 40th Armor Regiment, and subordinated to the 191st Infantry Brigade in Arizona. Final designation was as 8th Battalion, 40th Armor Regiment on 12 September 1963. On 12 January 1994, the Tucson Citizen reported that the unit's function would be transferred to the Nevada Army National Guard. The unit had been headquartered in at the Tucson Reserve Center. '..The 8th Battalion 40th Armor’s mission will be transferred to Nevada. The battalion, with headquarters in Tucson, is slated to be shut down and its mission transferred to Nevada, according to congressional sources. Congressman Jon Kyl, R-Phoenix, said yesterday that officials associated with the 63rd U.S. Army Reserve Command briefed members of the 8/40 over the weekend and, for the first time, informed members of the unit that it will be deactivated. Kyl said mission functions, but not personnel, from the armored unit are set to be transferred to the Nevada National Guard. Kyl said Pentagon officials indicated the deactivation will take effect in 1997. Closure of the 8/40 could result in the loss of 642 Army Reserve positions in Arizona. The unit has companies in Phoenix and Fort Huachuca that also would be closed under the plan. The unit inactivated in September 1996.
On 14 October 2005, the Army re-activated the 1st Battalion as a reconnaissance squadron designated 1st Squadron, 40th Cavalry Regiment, part of the 25th Infantry Division, and based at Fort Richardson, Alaska. The squadron has since served in the wars in Iraq and Afghanistan.
