Troop D, 17th Cavalry was initially in Vietnam as the ground reconnaissance element of the 199th Infantry Brigade (Light), arriving on 13 December 1966 and departing on 12 October 1970. The unit was raised as an air cavalry troop from the assets of Troop D, 3d Squadron, 5th Cavalry to support the 101st Airborne Division. This second tour lasted from 15 December 1971 to 20 March 1972. Finally, the unit was activated again on 30 April 1972 using the assets of Troop D, 1st Squadron, 1st Cavalry to serve the 11th Aviation Group at Da Nang. It departed Vietnam on 26 February 1973.