Army of the Republic of Viet Nam
The main ground force of the Republic of Viet Nam in the Vietnam War, was commonly called the Army of the Republic of Viet Nam (ARVN). There were smaller separate Air Force (e.g., RVNAF) and Navy branches, but ARVN was used generically for the RVN armed forces as well as for the Army. Its major U.S. counterpart headquarters was Military Assistance Command, Vietnam.
To varying extents, some of the leadership came from roles in the French military, or from groups that resisted the World War II Japanese invasion. That the ARVN had been fighting for many, many years affected its motivation and culture.
- Joint General Staff
Early command structure
President Diem appointed the Secretary of State for National Defense and the Minister of the Interior. The Defense Secretary directed of General Staff chief and several special sub-departments. The General staff chief, in turn, commanded the Joint General Staff (JGS), which was both the top-level staff and the top of the military chain of command.
There were problems with the military structure, even before considering the paramilitary forces under the Interior Ministry. The JGS itself had conflicting components with no clear authority. For example, support for the Air Force came both from a Director of Air Technical Service and a Deputy Chief of Air Staff for Matériel. The Director was, in principle, under the Chief of Staff., but actually reported to the Director General of Administration, Budget, and Comptroller for fiscal matters).
Combat units also had conflicting chains of command. A division commander might receive orders both from the corps-level tactical commander who actually carried out the operational art role of corps commanders in most militaries, but also from the regional commander of the home base of the division — even if the division was operating in another area. The chiefs of branches of service (e.g., infantry, artillery), who in most armies were responsible only for preparation and training of personnel of their branch, and orders only before they were deployed, would give direct operational orders to units in the field.
Ground forces and organization
An early structure, before large buildups, included: 
- Three corps headquarters and a special military district:
- Seven divisions of 10,450 men
- three infantry regiments
- artillery battalion
- mortar battalion
- engineer battalion
- company-size support elements
- Airborne group of five battalion groups
- four armored cavalry "regiments" (approximately the equivalent of a U.S. Army cavalry squadron)
- one squadron (U.S. troop) of M24 light tanks
- two squadrons of M8 self-propelled 75-mm. howitzers
- Eight independent artillery battalions with U.S. 105-mm, and 155-mm. pieces.
ARVN forces in the field were organized as four Corps, although these were geographically organized tactical zones rather than the more common use of corps as an operational headquarters commanding several divisions.
- I Corps tactical zone: Northern areas
- II Corps tactical zone: Central areas, including the Montagnard Central Highlands
- III Corps tactical zone: Saigon capital area
- IV Corps tactical zone: Mekong delta
Rangers, Airborne, and Marines were elite troops under headquarters control; there were small specialized units such as the LDNN (combat divers, comparable to U.S. Navy SEALs of the Navy.
The Luc Luong Dac Biet, Vietnamese Special Forces did have a conceptual politicomilitary and village-oriented function similar to United States Army Special Forces, but, especially under Diem, they acted as a political police while also having special operational functions. Over time, they evolved into a counterpart to the main U.S. Special Forces units and spawning various special missions units. By the time of Vietnamization, the original SF counterpart mission was gone, and LLDB personnel went into ARVN units - either as Border Guard Rangers or regular Rangers - as well as special operations units such as the Strategic Technical Directorate.
The Vietnamese Navy operated small coastal and river patrol craft.
They had a small but competent naval special operations unit modeled after the United States Navy SEALs, the Lien Doi Nguoi Nhai (LDNN).
- Collins, James Lawton, Jr., Chapter I: The Formative Years, 1950-1959, Vietnam Studies: The Development and Training of the South Vietnamese Army, 1950-1972, pp. 9-10