1964, he was promoted to lieutenant colonel. In April 1965, he handed over Gò Công province to his successor. Returning to the Infantry, he was promoted to Colonel, and he was appointed to be commander of the 7th Infantry Division. On June 19, 1966, Armed Forces Day, he was promoted to Brigadier General. In October 1966, he was appointed head of the delegation along with Brigadier General Phạm Quốc Tâm, commander of the 5th Infantry Division, to guide the delegation on an official visit to Taiwan. On June 19, 1968, he was promoted to major general. In early July, he was appointed commander of the IV Corps and Fourth Corps Tactical Zone. On May 2, 1970, Thanh flew in a helicopter to direct the Cửu Long (Mekong) offensive operation over the Cambodian border to destroy communist sanctuaries. His helicopter collided in midair with a U.S. Cobra attack helicopter ten miles inside Cambodia. Thanh was killed aged 39. General Thanh viewed by American Commanders Colonel Sidney Bryan Berry, senior adviser to the 7th Division in 1965, had described Thanh as an "aggressive" commander with "sound tactical sense" who "knows when to commit his reserve" and "has a deep understanding of the war and his division." In 1967 he was rated by COMUSMACV General William Westmoreland as the best ARVN division commander. However, Civil Operations and Revolutionary Development Support (CORDS) advisers differed and in 1967 found "his personal cautiousness and reluctance to push the battalions [those in securing missions] into more offensive activities... difficult to understand," claiming that he discouraged the initiative and aggressiveness of his subordinates." CORDS chief Robert Komer agreed and in 1968 described Thanh as unaggressive, unimaginative, and "rather a xenophobe." Major General George S. Eckhardt, a senior IV Corps adviser in 1968 and 1969, related Thanh's popularity when the two generals flew to My Tho, Thanh's previous 7th divisional headquarters, for a quiet lunch. When people learned of their presence, they crammed into the restaurant to welcome his return. For over half an hour, "Thanh bowed and shook hands with the stream of well-wishers." Brigadier General George Wear commented, "When the ARVN troops were well-led they fought as well as anyone's soldiers." Thanh was one such commander. According to COMUSMACV General Creighton Abrams, on May 20, 1970 tape, "The handling of the forces and the tactics by all the forces in IV Corps can only be described as