CBO’s Interactive Force Structure Tool

The Congressional Budget Office has estimated the operating costs (and number of assigned personnel) for every major combat unit in the U.S. armed forces. (Learn more about CBO's approach to calculating those costs.) This interactive tool is intended to illustrate the relationship between the size of the Department of Defense's (DoD's) total budget and the kinds of forces that the military fields. Users can adjust DoD's total budget (on the "Overall" tab) to see the effects on the size of the force, or they can adjust the size of the force (on the tabs for the military departments) to see the effects on budgets and forces. The tool is based on CBO's estimates of operating costs for major combat units. It also includes much simpler and more aggregated representations of DoD's spending to develop and acquire new weapons and to construct military facilities and other infrastructure.

See an example of how to use this tool

Editing the Department of the Armydirectly

Active-Component Brigade Combat Teams: 32

Editing the Department of the Navydirectly

Ships: 235

Editing the Department of the Air Forcedirectly

Squadrons: 212

The numbers shown below represent notional squadrons of 12 aircraft each. The total quantity for each type of squadron has been rounded to the nearest whole number.

Editing the Department of Defense's defensewide activitiesdirectly

What does this tool estimate?

Depending on users' input, the tool will either show the change in total DoD funding and personnel needed for a particular force (including users' specified levels for acquisition and infrastructure funding) or show the change in total DoD forces and personnel associated with a particular budget target. The change from DoD's planned budget can be specified either as an annual budget target for the 10th year (a change to the top line) or as a cumulative 10-year targeted change, which is more commonly used for budgetary decisions.

If users want to fine-tune alternative budget proposals, they can move or lock any slider to a given value, and changes to the total budget will reflect that specified value. That feature is intended to let users adjust the total budget in a more targeted manner than the tool's default behavior. (See a step-by-step example of how to use this tool.)

Costs are specified over a 10-year period, but the speed with which changes to the budget are implemented will alter the total 10-year costs or savings from any change. The tool's default is a 5-year implementation time line, which CBO believes is generally a reasonable assumption. However, users may specify faster or slower implementation time lines (from 3 to 7 years).

The values generated using this tool are illustrative and are not official CBO cost estimates.

What types of costs are included in the tool?

This tool primarily estimates total operation and support (O&S) costs, which are the costs associated with the day-to-day running of military units. O&S costs make up about 60 percent of DoD's budget. (The rest is mainly costs to acquire weapon systems and construct buildings and other infrastructure.) O&S costs include compensation for military personnel, which is paid from the services' military personnel accounts. O&S costs also include compensation for most of the military's civilian employees, health care costs for military and civilian personnel, and the expenses of running a unit (such as day-to-day operations, equipment maintenance, training, and support contractors). All of those costs are paid from the services' or defensewide operation and maintenance accounts.

O&S costs are very closely related to the size of units. For instance, a unit with 10,000 military personnel will have military personnel costs commensurate with that size, and DoD has a limited ability to change those costs, particularly in the near term.

The tool's values for the personnel and costs of individual types of units are annual averages over the fiscal year 2021-2025 period. Those values include direct personnel and costs, which are directly associated with a major combat unit; indirect personnel and costs, which are associated with units that support the major combat unit; and overhead personnel and costs, which are associated with the major combat unit's share of administrative or overhead activities. In the tool's results table and graphs, costs shown for the 10th year or as a cumulative 10-year total are based on the average annual cost, adjusted for projected cost growth (above the rate of inflation) over the next 10 years.

For completeness' sake, this tool also includes sliders with values for each military department's acquisition and infrastructure budgets, as if those activities were additional major units. (No military personnel costs are associated with acquisition and infrastructure budgets, however, because those personnel are funded elsewhere in the defense budget.) Changing the slider associated with any type of major combat unit will not affect a department's acquisition and infrastructure budgets, but users can alter those budgets separately. Changing DoD's total budget, however, will cause the tool to adjust the acquisition and infrastructure sliders to reflect the changes in those budget accounts that would be proportional to the change in the total budget.

A spreadsheet containing CBO's estimates of personnel numbers and costs for each type of major combat unit over the 2021-2025 period is available below (titled "Data Underlying Appendix Tables in the U.S. Military's Force Structure: A Primer, 2021 Update").

Where do the numbers in the tool come from?

For 2021 to 2025, the total costs of the force are based on the projected costs in DoD's budget request for that period, the 2021 Future Years Defense Program (FYDP). Those costs, which are shown in 2021 dollars, include all costs except those marked as "Anticipated OCO" (for overseas contingency operations). For years after 2025, total costs increase in a manner consistent with DoD's plans and CBO's analyses of the long-term implications of those plans.

If a user downloads raw data using the "Export 10-year data (as .csv)" button, the resulting file will include costs for the 5-year period of the FYDP and the following 5 years, as well as the real growth rate used to transform average costs from the FYDP into costs for each year of that 10-year period. Annual costs, and any changes to them, are based on the cost in the 10th year of that period.

The costs for individual units shown in the pop-up boxes are average annual costs over the 5 years of the FYDP. Those costs are for display purposes only. For all calculations and outputs, the tool internally converts those costs to the relevant year using an escalation rate. That conversion is necessary because costs change from year to year as a result of pay raises and other factors, so there is no single cost value for a unit over the full 10-year period. The quantities shown for individual units are also averages over the 5 years of the FYDP.

Any unit or slider shown as a percentage (all of which have a planned value of 100 percent) represents some element of the force or budget that is not best described as a specific number of forces. For example, "Classified Defensewide Funding" represents funding for a wide variety of classified programs. In such cases, the simplest description is to present the planned force as having 100 percent of its planned funding and then let users adjust that funding to the percentage they feel is appropriate (for example, setting classified defensewide funding at 90 percent or 110 percent of the currently planned funding).

What types of units are included in the tool?

This tool focuses on the same types of units as CBO's force structure primer: high-level combat units that exist in the current force. Like the primer, the tool presents all unit costs and sizes as they are in DoD's 2021 budget request. In some cases, the selection of unit types was limited by the amount of detail in DoD's budget documents.

Any choice of which high-level combat units to include reflects a judgment about whether a type of unit will be prominent enough in planning discussions to merit being the focus of policy choices. In general, CBO assumed that less prominent types of units (of which DoD has thousands) would have their numbers adjusted in a manner consistent with policy choices about more prominent units. For example, the Army has many types of brigades that are traditionally assumed to support brigade combat teams (BCTs). CBO judged that those types of brigades did not need be shown independently because the Army would most likely adjust their numbers accordingly if the number of BCTs changed. Hence, the tool makes such adjustments automatically to indirect personnel and costs. In different contexts, however, some of those brigades (such as artillery brigades that can provide long-range fire) might be seen as prominent separate combat elements, not as support units for BCTs.

Because CBO based all unit costs and sizes on DoD's 2021 budget request, the tool does not include any hypothetical or potential future types of units. In some cases, DoD's plans call for introducing new types of units in the future (such as squadrons of B-21 bombers for the Air Force). But if those units are not included in DoD's budget documents, CBO has no official basis for providing DoD numbers for their cost or size. That does not mean it would be impossible to produce estimates for such units, only that the estimates-unlike all other unit costs and sizes presented here-would not be grounded in DoD's official plans.

In addition, CBO could not distinguish between certain types of current units because of a lack of detail in DoD's budget documents. For example, although CBO presented some units in the Army National Guard and Marine Corps Reserve separately from units in the active components of those services, it could not do the same for units of the Air Force Reserve and Air National Guard, because of the way in which the Air Force structures its units and presents their budgets.

Why might some forces not change proportionally when I change DoD's budget?

By default, the tool will try to alter the force in a proportional manner (that is, all forces will be changed by the same percentage). The changes might not be proportional in all cases, however, because of limits that CBO included in the tool. For example, some types of major units cannot be altered freely over short time periods, so CBO limited the extent to which sliders for those units could move. CBO also restricted the size of some changes if they might alter DoD's costs beyond the limits of CBO's analytic model of the military's costs, which underlies this tool. When users adjust DoD's total budget, such limits may cause some types of changes to vary in ways that are not proportional to the current force. (For more details about those limits, see the next answer.)

In addition, small changes to DoD's budget may result in greater-than-proportional changes to less expensive units because treating the number of units as integers restricts the level of detail that the tool can present. For example, a budget cut of $5 billion in the 10th year might lead to reductions in a few small units (such as National Guard brigades) but no large units (such as active-component brigades) because cutting even a single large unit would produce disproportionate savings.

Why can't I increase or decrease some elements of the force?

In many cases, CBO judged that it would be unrealistic to allow the force to vary beyond certain parameters in the next 5 to 10 years. For example, some models of aircraft, such as B-52 bombers, no longer have an active production line, so it would be extremely difficult to procure more of those aircraft. For aircraft carriers and some other ships, it is unlikely that the shipbuilding industry could produce an additional ship in the relevant time frame-either because of constraints on the industrial base or because of the time required to build and commission such ships (9 years for an aircraft carrier).

In most cases, CBO also placed a general limit on changes beyond a certain size. Analytic models are generally most accurate when they attempt to model variations on changes that have occurred in the past. However, for most types of major combat units, there are no recent examples of those units being rapidly increased or decreased by very large amounts. Thus, it would be inappropriate to suggest that CBO's model could accurately represent changes significantly larger than those allowed under the general limits included in this tool.

Why does the tool use notional squadrons of aircraft?

In the Air Force and Navy, squadron sizes vary greatly even for the same type of aircraft, making counts of those squadrons an unreliable measure of force structure. To compare costs and personnel among squadrons, CBO's force structure primer translated all Navy and Air Force squadrons into notional squadrons of 12 aircraft.

In previous versions of this interactive tool, that approach caused the tool to display fractional squadrons of aircraft. For example, the Air Force's 2 squadrons of 8 B-2 bombers each (16 aircraft) became 1 and 1/3 squadrons (a notional squadron of 12 aircraft and 4 additional aircraft).

In this version of the tool, for ease of use, CBO instead followed the practice used in the primer and rounded notional aircraft squadrons to the nearest whole number. Thus, the B-2 fleet is shown not as 1 and 1/3 squadrons but as a single squadron, with its cost and personnel numbers adjusted accordingly.

Why don't changes to specific forces cause changes to acquisition or infrastructure funding?

CBO's model of the military's costs, which underlies this tool, focuses on operation and support costs. Changes to the force structure do not tightly constrain DoD's acquisition budget in the same way that they constrain the O&S budget. In some cases, changes to forces would have predictable effects on acquisition costs. For example, adding F-35 squadrons would require buying more F-35 aircraft. But in other cases, the military has some flexibility in deciding how changes to forces would affect its acquisition costs. For instance, the Navy can sometimes choose to increase the size of a fleet by either purchasing new ships or deferring the retirement of older ships. The Army can choose between equipping forces with current equipment, upgrading that equipment, or buying new equipment. Moreover, to be effective, a unit can require much more acquisition than simply its own equipment (new fighter aircraft are much more useful when also armed with precision munitions). DoD often chooses to upgrade or modify existing platforms to improve their performance in various ways.

Because DoD has many options available that would produce very different acquisition costs for a given force structure, CBO decided to have this tool show the acquisition budget as 100 percent of planned funding and let users adjust that percentage separately from their changes to the force structure. CBO followed the same practice for the military construction budget, which funds infrastructure, because DoD has similar flexibility with its construction funding and basing decisions.

How does a formal CBO cost estimate differ from the costs shown here?

The costs shown in this tool reflect averages for DoD's units over the 5 years of DoD's 2021 budget request. Thus, they are "generic" annual costs that should approximate, but not equal, the costs of specific units in specific years.

By incorporating many simplifying assumptions and focusing on a 5-year period, those average annual costs reflect a more abstract approach than the one CBO uses to estimate the costs of legislation. That simplified approach allows CBO to make comparisons among all elements of the force structure. Such an approach is generally appropriate for rough estimates used for planning purposes, but it is not the way CBO would evaluate a specific proposal to change DoD's budget. For such a proposal, CBO would consider the exact legislative language, the proposed timing of the change, the statutory and Congressional rules that govern CBO's estimates for proposed legislation, and many other factors to produce an estimate specific to that proposal.

To generate illustrative average annual costs (as this tool does) without specific bill language, CBO's estimates employ some assumptions about the ways in which legislation might direct DoD to change its force structure. For example, consider a hypothetical authorization bill that would forbid DoD from retiring a class of ships or a type of aircraft-an approach analogous to using this tool to increase the size of the CG-47 cruiser force. (The increase allowed by this tool reflects the possibility of keeping existing CG-47 cruisers by delaying their retirement rather than producing new CG-47s.) For the purposes of this tool, CBO has assumed that such a directive would come with a change in the Navy's total number of military personnel and with a corresponding change in the appropriations that pay for those personnel. Similarly, consider a hypothetical authorization bill that would expand DoD's purchases of a type of aircraft to equip Air National Guard units. For the purposes of this tool, CBO has assumed that any change in force structure would be implemented so as to preserve the current balance of units between the active and reserve components. In an official cost estimate, by contrast, CBO might not estimate a change in authorizations for military personnel appropriations.

• Data Underlying Appendix Tables in the U.S. Military's Force Structure: A Primer, 2021 Update
• Data Underlying Figures and Supplemental Data for the Long-Term Implications of the 2021 Future Years Defense Program

• The U.S. Military's Force Structure: A Primer, 2021 Update
  May 20, 2021
• Long-Term Implications of the 2021 Future Years Defense Program
  September 9, 2020
• The U.S. Military's Force Structure: A Primer
  July 29, 2016

CBO seeks feedback to make its work as useful as possible. Please send comments to [email protected].

Casey Labrack, Adam Talaber, and F. Matthew Woodward developed this interactive tool with guidance from David Mosher and Edward G. Keating. Several people within and outside CBO viewed earlier versions of it and provided helpful comments. Bernard Kempinski (formerly of CBO) created the graphics that appear with the descriptions of the units. Mark Doms and Robert Sunshine reviewed the tool, and Christian Howlett edited it. Rob Dean integrated the tool into CBO's website and prepared it for release.

This page was last updated on May 17, 2022; the underlying data, which can be found in CBO's report The U.S. Military's Force Structure: A Primer, 2021 Update, are based on DoD's fiscal year 2021 budget request.

Suggested citation: Congressional Budget Office, "CBO's Interactive Force Structure Tool" (May 17, 2022), www.cbo.gov/publication/54351.