In late 1965 Major general Lewis W. Walt, the commander of the U.S. III Marine Amphibious Force and the I Corps senior advisor said that the 1st Division under Chuân was "waging a skillful campaign" and "consistently destroying the VC in all significant encounters.
"[1]: 113 On 14 March 1966 he was appointed commander of I Corps, which oversaw the northernmost part of the country, replacing Nguyễn Chánh Thi.
[1]: 129 The replacement of the popular Thi by his military rival Nguyễn Cao Kỳ sparked the Buddhist Uprising and Chuẩn supported the Struggle Movement against the junta in Saigon.
On 9 April Kỳ replaced Chuẩn with Lieutenant general Tôn Thất Đính in an attempt to shut down the opposition.
[1]: 133 [2] On 9 July 1966 a special military tribunal retired Chuân, Đính, Thi and other officers involved in the uprising.