This tutorial will walk you through how to use the various options in the Congressional Budget Office’s Interactive Force Structure Tool to create a scenario that matches the particular policy choices you want to explore.
For the purposes of the tutorial, we’ll use an illustrative scenario. The scenario is intended purely to show how the tool can be used. In other words, it isn’t some real policy proposal that we intend to evaluate seriously; it’s simply a learning exercise.
Step 1: Define Your Goals
The interactive tool can be used to explore simple “what if” changes (such as “what if we added an aircraft carrier?” or “what if we cut an armored brigade?”). In most cases, though, the tool will be more useful if you have a clear vision of what you're trying to learn about. That vision can take various forms. For example:
- You may primarily be interested in the effects of adding to or cutting the Department of Defense's (DoD’s) budget, or
- You may primarily have a vision of a particular type of force and be curious about how moving to that type of force would affect DoD's total costs, or
- You may be interested in seeing what different types of forces DoD could sustain with a budget similar to its current one.
For the purposes of this tutorial, we're going to assume that we want to explore a large cut to DoD's overall budget—decreasing currently planned funding by about 10 percent. We don't want that cut to just reduce everything by 10 percent, though. We're going to focus the cuts mostly on reducing higher-end (and higher-cost) elements of the force, to see if we can maintain a robust force structure with less funding. In this sample scenario, we're trying to preserve lower-end and lower-cost elements of the force.
Step 2: Make Broad Adjustments—Using “Change the Overall Budget”
The first element of our sample scenario is to make a large cut, so we'll just enter the large cut first and then fine-tune it later. Open the interactive tool in your web browser and, on the Overall tab, find the header called Change the overall budget by. Here, we can adjust either DoD's projected annual budget 10 years from now (the end of the usual Congressional budgeting period) or DoD's total budget over 10 years. For this tutorial, let's accept the default setting and adjust the annual budget in the 10th year. We've decided that we want to see whether we can maintain a lower-cost, but still robust, force by shifting to a greater reliance on more basic forces. The total change in costs over the next decade isn't very relevant for that purpose.
We decided earlier that we want to reduce DoD's annual budget by about 10 percent. In the View Results table, we can see that DoD's planned force is projected to have an annual cost of about $889 billion 10 years from now. So we'll make sure to select “in the 10th year” for the type of change and then type in -89 (about 10 percent) for the size of the change.
As soon as we do that, several things in the tool change. You should now see, in the View Results table, that DoD's planned force has an annual cost of $888.8 billion in the 10th year, our custom force has an annual cost of $799.8 billion, and the difference is a reduction of $89 billion. The two results graphs—Total Costs and Number of Military Personnel—also now show cuts to each of the military departments: the Army, the Navy (which includes the Marine Corps), and the Air Force (which includes the Space Force).
To see how such a change might affect each of the military departments, you can go back up to where you clicked on the Overall tab and click on any of the departments. You'll notice that most of the sliders on the tabs for units in the military departments have been adjusted downward by about 10 percent. You can tell they've changed because the white circle (which represents the unit quantity or funding percentage in our custom force) has moved from the dark dot (which represents DoD's planned force). There are also negative numbers next to each slider, showing how much they've been reduced.
This is the interactive tool's default behavior when you change DoD's overall budget. The tool will try to spread the cut or addition in a proportional manner that preserves, as much as possible, the relative sizes of the different elements of the force. The tool can't always do that exactly. CBO included what it considers plausible limits on the minimum and maximum values allowed for each element of the force. For example, you can't increase the size of the B-52 force by 10 percent, because B-52s haven't been produced for decades, so it would be difficult to start building them again in the next decade.
For the purposes of this tutorial, we don't want to simply spread the total budget cut around in a proportional manner. So we'll fine-tune it a bit.
Step 3: Make Finer Adjustments—Using Sliders, Undo, and the Lock Buttons
For this scenario, we decided initially that we wanted to focus our cuts on higher-end units with higher costs. So let's go to the tabs for the different military departments and find units that look particularly pricey.
Selecting the Army tab, we can see different types of Army units. For each type, we can hover the cursor over the ? icon next to the unit’s name and see a quick description of that type of unit. We can also see the average annual cost and number of military personnel for that type of unit, including the unit’s share of support forces and administrative activities. (Those average annual costs and personnel numbers are based on DoD’s budget request for fiscal years 2024 to 2028. Fuller descriptions of the units and their costs can be found in The U.S. Military’s Force Structure: A Primer, 2021 Update, and a table with all of the units’ costs can be found under the Data and Supplemental Information header near the bottom of the tool.)
Looking at costs per unit, it's clear that Active-Component Armored Brigade Combat Teams (BCTs) are the most expensive type of unit in the Army ($3 billion apiece). The total budget cut that we entered in step 2 has automatically reduced the number of armored BCTs in the Army's active component from 11 to 10. We can reduce those units much more by clicking on the white circle in the middle of the slider and pulling it all the way to the left before releasing it. It now shows the number of armored BCTs reduced from 11 to 6—a larger cut.
We want to make sure that the change sticks and doesn't automatically get adjusted when we make other changes later. So we can click on the small lock icon next to the armored BCT slider. That will lock the slider at the value we selected.
Next, we can do the same thing on the Navy tab with that department's most expensive units, Carriers and Carrier Air Wings. Pulling those sliders all the way to the left will reduce the number of carriers to 7 and the number of carrier air wings to 5. We'll lock the sliders at those values as well.
Finally, we'll go to the Air Force tab and reduce the number of F-22 Fighter Aircraft Squadrons to 8 and B-2 Bomber Squadrons to 0. We'll lock in those values too.
All of those adjustments have resulted in a larger budget cut than we initially entered. (We did, after all, just go and make bigger cuts to those forces than the default changes allocated to them.) Scrolling back up to the View Results table, we can see that we're now reducing DoD's annual budget in the 10th year by $120.6 billion, rather than the $89 billion we started with. If we check the Change the overall budget by header on the Overall tab again, we see that the -89 we entered has been adjusted to -121.
Thinking back to our original plan, we weren't trying to cut the defense budget by more than 10 percent. We were hoping to preserve more basic forces by disproportionately cutting high-cost elements of the force. So we're going to change the target budgetary change back to -89. That will automatically adjust every element of the force that can be adjusted, except the elements that we locked. Overall, given the savings on high-cost elements of the force that we've locked in, going back to an overall target of -$89 billion will cause everything else in the force to be cut by about 6 percent now, instead of the original 10 percent in step 2.
Step 4 (Optional): Modify the Initial Results
At this point, we've learned something. We could preserve more of our lower-cost units by disproportionately cutting higher-cost units, but doing that changes the lower-cost units from getting a 10 percent cut to getting a 6 percent cut. The preservation effect from focusing our cuts on higher-cost units wasn't really that large—certainly not big enough to let us retain the current number of lower-cost units in the force.
This is where we could make more modifications. Maybe we didn't identify and cut enough higher-cost units. We could repeat the adjustments in step 3 with other higher-cost units (for example, retiring all Zumwalt Class Destroyers or B-1B Bomber Squadrons as well).
Alternatively, we could decide that we're trying to make too large a total cut to DoD's budget. Instead, we could reduce the target budgetary change to a smaller amount, to see just how big a cut we could make without affecting the lower-cost units.
All of those approaches would be ways to explore what we've learned: that because DoD has many different types of units, and its costs aren't dominated by just a few high-cost units, large cuts to the defense budget would probably require broad cuts to many different types of forces. If we want to protect large parts of the force from being reduced, either we have to be willing to disproportionately cut a lot of other units to compensate, or we have to accept a smaller cut to the total budget than we might otherwise prefer. A similar logic would apply in reverse to increases to the force: adding only a few high-cost units would not produce large budgetary increases, but broad increases to the force would.
Step 5: Export Your Results for Further Analysis
Once you have a scenario you're happy with, you could simply jot down the results—the number of each type of force, everything in the View Results table and graphs, and so forth. But that would be a lot of numbers to write down if you wanted to preserve your scenario for the future! And it wouldn't be very convenient if you wanted to do some further work with your scenario that the interactive tool doesn't support.
Instead, you can scroll down to the Download header and use the two buttons labeled Export custom data (as .csv) and Export 10-year data (as .csv). Each of those buttons will download a .csv (comma separated value) file to your computer. Those files contain all of the data you would otherwise need to jot down manually, and they can be opened easily in a spreadsheet or other program.
The first file, custom-data_CBO-armed-forces-tool_[date].csv, provides all of the information about the forces in your scenario. It includes DoD's planned numbers of different types of units, your customized numbers, the costs and sizes of those units, and the changes to those costs and sizes resulting from your scenario. The costs shown in that file are annual costs 10 years from now.
The second file, ten-year-data_CBO-armed-forces-tool_[date].csv, provides a table of the total costs of the planned force and your custom force over the next 10 years. The costs in that file are shown in 2024 dollars on a year-by-year basis. The real growth index (that is, the growth index adjusted to remove the effects of inflation) included in the file is the relative value of each year's costs compared with the 10th year's costs and is used to construct values for the current and custom forces in the 10-year table. The calculations also incorporate a phase-in value to represent the fact that it would take DoD time to make changes to the force structure, so costs or savings wouldn't appear immediately. (The value of the phase-in and real growth index, multiplied by each other and then by the 10th-year costs or savings, provides the change from DoD's current plan. That is, by the end of the phase-in period, the change to the budget—expressed as a percentage of DoD’s total budget—will be fully implemented and remain so for the remainder of the 10-year period.) The default phase-in value is 5 years, unless a user chooses a different value when making a cumulative 10-year budgetary change. The gross domestic product deflator that CBO used to convert DoD's budget data into real dollars is provided for users who wish to transform real dollars into nominal dollars. (That deflator comes from CBO's July 2023 economic projections.)
All of the data provided in those files are the same type of data used in the CBO cost model underlying the interactive tool. That means you can replicate and alter the basic model (multiplying costs by the quantities of each element of the force and then summing those costs).
CBO received suggestions from many reviewers about things they'd like to see the model do. CBO hasn't been able to incorporate all of those suggestions. But with a custom spreadsheet using the data from the .csv files, you could make a number of additional changes:
- Focusing on different types of units. For instance, CBO chose to include Army support brigades in the total costs and personnel numbers for brigade combat teams. But if you have some ideas about the cost and size of engineering brigades, for example, you can cut that chunk of support out of the BCTs and make it a separate element of the force.
- Adjusting units' costs. For simplicity, CBO chose to assume that changes to the force would not change units' readiness, or the pay and benefits of personnel, from the levels included in DoD's budget plans. But if you want to explore changes to readiness, you can adjust unit costs upward or downward to see what the effects would be. If you want to explore the effects of making changes to military compensation, you can slow its growth to better match DoD's goals or increase it faster than CBO projects it will rise. (CBO provides examples of different ways to slow the growth of military compensation in its Budget Options volumes and Budget Options web page.)
- Making detailed changes to acquisition funding. The interactive tool is largely based on DoD's operation and support budget, which excludes funding to acquire weapon systems or construct military facilities and other infrastructure. CBO included acquisition and infrastructure funding as if they were elements of the force to allow the tool to show DoD's total budget. For various technical reasons, those funding categories vary with the overall size of the budget but are not currently linked to specific changes in the force. But if you have some ideas about the costs of an acquisition program, you can make such linkages by directly changing the value of the relevant acquisition entry on your spreadsheet (for example, “if we cut the number of aircraft carriers, we could also skip purchasing new carriers”). CBO's Budget Options volumes and web page and some of its other reports provide various examples of how one might cut forces and acquisition.
- Creating more detailed graphs. The graphs included in the tool, which show changes to the total costs and number of military personnel by military department, certainly aren't the only way to display the data. With data from the .csv files, you can present DoD's forces and budgets in whatever manner you prefer.
The point of the exportable data files is to document the values used in the model—for both DoD's planned force and a user's custom force—in a transparent and convenient way that other analysts, researchers, or students can use for their own purposes. So feel free to do that!