The 1st Cavalry Division entered Qui Nhon, South Vietnam, on Sept. 11, 1965. Its arrival brought U.S. Army troop strength in the country to over 125,000.
The 1st Cavalry was the first full division sent to South Vietnam. Along with nine battalions of airmobile infantry, the division included an air reconnaissance squadron, six artillery battalions and three aviation battalions. Two months after arriving, at the Battle of the Ia Drang Valley, the division participated in the first major engagement between U.S. and North Vietnamese forces.
The 1st Cavalry Division was the only division to fight in all four Army corps tactical zones during the Vietnam War. Most of the division started to leave South Vietnam in April 1970, although one brigade remained until June 1972.