On April 12, 1964, three battalions of Viet Cong invaded Kiên Long, quickly overrunning the entire district. Upon gaining control of Kien Long, they executed the district chief and his family. The Army of the Republic of Vietnam, augmented by air support from the United States, responded to the invasion in force. Although the Viet Cong were operating in blind daylight, they were able to hold their own against both the South Vietnamese soldiers and the American aircraft. After eight days of fierce combat in which heavy casualties were inflicted on both sides, the Viet Cong abandoned the district and were able to withdraw from Kien Long in an orderly fashion.
Both the ARVN and Viet Cong took heavy casualties in the fight for Kien Long. Nationwide, the ARVN took one thousand casualties (200 dead, 660 wounded, and 140 missing) from April 12 to April 20; a quarter of these were suffered at Kien Long. Additionally, the battle held major strategic significance as it marked one of the very first times that large numbers of Viet Cong would successfully operate simultaneously and openly in broad daylight.