The U.S. Military’s Force Structure: A Primer, 2021 Update

To increase understanding of the choices that the nation faces when considering the defense budget, the Congressional Budget Office has updated its 2016 primer on the structure of the armed forces. This updated version is based on the spending plans and personnel numbers outlined in the Department of Defense’s (DoD’s) Future Years Defense Program for fiscal years 2021 to 2025.

The primer contains entries that describe the size, costs, and functions of every major element of the military’s force structure. Those elements include the major combat units that form the traditional backbone of the armed forces, such as armored brigades, aircraft carrier strike groups, and tactical aircraft squadrons. They also include specialized organizations that provide specific capabilities to DoD, such as special-operations forces and missile defense.

CBO’s analysis of the military’s force structure focuses on the day-to-day operating costs covered by DoD’s operation and support (O&S) budget. That budget, which has typically totaled more than $400 billion a year in recent years, excludes spending to buy weapon systems, build military facilities, and conduct ongoing military operations.

For this analysis, CBO examined the activities, funding, and personnel covered by the O&S budget and ascribed them to major elements of the force structure. For major combat units, the estimates of costs and personnel numbers include a combat unit’s many supporting units and their combined share of administrative or overhead activities. The resulting estimates of “fully supported units” give policymakers who are interested in changing the military’s force structure a sense of the costs and personnel numbers that those changes would involve.

The primer is organized as follows:

• Chapter 1 describes CBO’s conceptual approach to analyzing the military’s force structure and costs.
• Chapter 2 discusses the Department of the Army, with descriptions of each type of brigade combat team.
• Chapter 3 discusses the Department of the Navy, with descriptions of major types of ships and Marine Corps units.
• Chapter 4 discusses the Department of the Air Force, with descriptions of major types of aircraft squadrons and the new Space Force.
• Chapter 5 describes some major defensewide organizations, such as Special Operations Command and the military’s health care system.

Each chapter also focuses on special topics that are important for understanding the military’s force structure, such as the integration of different types of units or the military’s ability to conduct certain kinds of operations.

The primer is designed to be a reference work with discrete entries that do not need to be read in sequence. After reading the overview of CBO’s approach in Chapter 1, someone interested in, for example, the structure of the Air Force or the cost of the Army’s infantry brigade combat teams can turn to the relevant section.