III Corps tactical zone
During the Vietnam War, the III Corps tactical zone (III CTZ) was an Army of the Republic of Viet Nam organization with geographic responsibility for Saigon and 11 surrounding provinces. It had had various earlier names, such as Saigon Military District. The are contained 38 percent of the population and 90 percent of the industry. 
These headquarters should not be confused with the ARVN Joint General Staff (JGS) and Military Assistance Command, Vietnam (MACV), also in the Saigon area at Tan Son Nhut. III CTZ reported to the JGS; II FFV reported to MACV.
- Corps is usually a tactical, rather than geographical structure; the U.S. renamed its Vietnam War corps formation s "field forces" to avoid confusion. In July 1970, the Republic of Vietnam redesignated its CTZs as Military Regions (MR). ARVN MR numbers, however, had no relationship to the People's Army of Viet Nam's MR numbering scheme.
- Oberdorfer, Don (1971), Tet! The story of a battle and its historic aftermath, Doubleday, p. 125