U.S. Army Units Explained: From Squads to Brigades to Corps

Christina Knight | October 11, 2017

Military terms like platoon, company, battalion, brigade may sound familiar, but do you know how many soldiers make up these units, and how they comprise one another? As America revisits the Vietnam era through narratives in the 18-hour PBS series The Vietnam War, it’s useful to understand just how many forces were involved in that war’s battles, down to the number of men. How many U.S. soldiers are in a squad? What groupings do major generals, lieutenant colonels, and captains lead? If you don’t have a connection to the U.S. Army, the size of Army units can be difficult to grasp and therefore, the human scale of war. While figures are flexible and can vary by war and assignment (armored, artillery, cavalry, ranger), here are some explanations about the U.S. Army structure.

U.S. Army Units graphic

U.S. Army

The U.S. Army is made up of its active regular Army and two reserve components—the Army National Guard and the Army Reserve. Since the end of the Vietnam War, the U.S. Army has been all-volunteer— meaning no one is drafted—and as always, everyone receives a salary.

Military Leaders in Vietnam

The three commanders of the U.S. forces during the Vietnam War were:
General William Westmoreland, from 1964 to 1968.
General Creighton Abrams, from 1968 to 1972.
General Frederick Weyand, from 1972 to 1973.

Field Army

A field army is the U.S. Army’s largest unit structure (50,000 and more soldiers). The last use of a field army was in 1991 during Operation Desert Storm, which took place in Iraq, Kuwait, and outlying areas of Saudi Arabia. A four-star general commands a field army. The five-star rank of general was retired in 1981 with the death of General Omar Bradley. The other five-star generals in the history of the U.S. Army were Generals Marshall, MacArthur, Eisenhower, and Arnold.

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The corps is treated as an operational unit of employment by the U.S. Army and can be comprised of 20,000-45,000 soldiers. Corps are commanded by the rank of Lieutenant General (LTG), a three-star general.

Corps in Vietnam

The U.S. Army, Vietnam (USARV) controlled all U.S. Army service and logistical units in South Vietnam until May 1972, when it merged with the Military Assistance Command, Vietnam (MACV) to become USARV/MACV Support Command.

The U.S. Army called its corps-level headquarters I Field Force and II Field Force to avoid confusion with the Army of the Republic of Vietnam (ARVN) corps areas. I Field Force, Vietnam was responsible for the 12 provinces of the Central Highlands and II Field Force, Vietnam was responsible for the 11 provinces surrounding Saigon (now Ho Chi Minh City). Both field forces were deactivated in 1971.


The number of modular units in an Army division is flexible and the total number of soldiers is 10,000-15,000. A two-star major general commands a division.

Divisions in Vietnam

Here are just some examples of divisions that served in the Vietnam War.

The 82nd Airborne Division, an elite infantry division specializing in parachute assault operations, entered Vietnam in 1966. The 101st Airborne Division (“Screaming Eagles”) fought in major battles including the Battle of Hamburger Hill in May 1969. Both airborne divisions were called to duty within the U.S. itself in 1967, to help quell the Detroit riot.

From 1966 to 1970, the 4th Infantry Division’s battles in Vietnam included the tough Battle of Dak To (1967-68).

Brigade or Regiment

Brigades are made up of 2,000-5,000 soldiers, normally split among three to five battalions. The armed cavalry and ranger forces of this size are called regiments or groups, not brigades. Commanders of brigades or regiments are one-star brigadier generals or colonels.

Brigade in Vietnam

Paratrooper from the 101st Airborne Brigade applying mouth-to-mouth resuscitation to an injured soldier who was airlifted by helicopter to the medical clearing station near Kontum, Vietnam. From The New York Public Library

The 173rd Airborne Brigade was the first major United States Army ground formation deployed in Vietnam, serving from 1965 to 1971 and losing nearly 1,800 soldiers. The 173rd is best known for the Battle of Dak To (1967-68), where along with the Marines, it suffered heavy casualties against the North Vietnamese. When the 173rd returned to the U.S. in 1972, some units became part of the 101st Airborne Division and the rest of the units were inactivated.


A battalion in the U.S. Army is normally made up of three companies and 300 to 1,000 soldiers, but can have up to five companies. An armored or air cavalry unit of similar size is called a squadron.

Company, Battery or Troop

A company in the U.S. Army is normally made up of three platoons, which means 60 to 200 soldiers, but it can have more. An artillery unit is called a battery and an armored air cavalry is called a troop. Leading a company, battery or troop is a Captain, 1st Lieutenant, or Major.

Company in Vietnam

The company in Vietnam that became infamous for the civilian massacre at My Lai in 1968 was the Charlie Company. Watch as the story is told in American Experience: My Lai.


A 2nd lieutenant commands a platoon, which is comprised of three to four squads (18-50 soldiers).


The squad is a soldier’s most intimate group, consisting of six to ten soldiers. A squad is commanded by a sergeant.

The Vietnam War, a 10-part, 18-hour documentary film series by Ken Burns and Lynn Novick, premiered on PBS stations Sunday, September 17, 2017. An immersive 360-degree narrative, the series tells the epic story of the Vietnam War as it has never before been told on film.

Another Vietnam-related documentary is American Medevac. During the Vietnam War, CBS News correspondent Morton Dean and cameraman Greg Cooke flew on a harrowing medevac mission to rescue three wounded infantrymen from an enemy infested rice paddy. Dean long wondered what had become of the medevac crew and the bloodied men who were airlifted to safety on that day in 1971. American Medevac tells the story of their reunion, more than 40 years later. Watch now.