The Potential Costs of 

Expanding U.S. Strategic 

Nuclear Forces If the New 

START Treaty Expires

AUGUST 2020

CONGRESS OF THE UNITED STATES

CONGRESSIONAL BUDGET OFFICE
At a Glance

The New START Treaty will expire in February 2021 unless the United States and Russia agree to extend it for 

up to five years. Expiration of the treaty would end several decades of continuous coverage under arms control agreements that limit strategic nuclear forces and provide transparency. If the treaty expired in 2021, the 

United States and Russia could respond by maintaining the status quo. Alternatively, they could take various 

actions to compensate for the lack of treaty limits, perhaps to address a real or perceived buildup of forces by 

the other party. 

The Congressional Budget Office was asked to examine what the costs would be if the United States pursued one 

type of outcome: increasing its deployed strategic nuclear forces from no more than 1,550 warheads as specified in New START to the levels specified in the three most recent agreements—the Moscow, START II, and 

START I treaties. Because forces could be expanded in many ways to meet those levels, CBO looked at a range 

of outcomes and their costs. 

• Expanding forces to Moscow Treaty limits (1,700 to 2,200 warheads) would not increase the Department 

of Defense’s (DoD’s) costs relative to its current plans, which call for fielding a new generation of strategic 

nuclear delivery vehicles to replace the current generation. CBO estimates that DoD’s production costs (not 

including development or operation costs) for implementing its current plans would total $240 billion over 

the next few decades.

• Expanding forces to START II limits (3,000 to 3,500 warheads) or to START I limits (6,000 warheads) 

could be accomplished by increasing the number of warheads on each missile (which CBO refers to as the 

lower-cost approach) or by increasing the number of delivery vehicles (missiles, submarines, and bombers), 

which CBO refers to as the more flexible approach, or by some combination of the two. 

• Increasing warhead loadings to reach the START II limits would incur about $100 million in onetime costs 

for DoD. Increasing the number of delivery vehicles while maintaining current warhead loadings would 

increase DoD’s onetime costs by up to $172 billion over several decades and annual operating costs by 

$3 billion to $8 billion. (All costs are in fiscal year 2020 dollars.)

• If DoD expanded forces to START I limits using the lower-cost approach, its onetime costs would rise 

by $88 billion to $149 billion and its annual costs by $4 billion to $10 billion. Under the more flexible 

approach, DoD’s onetime costs could increase by $410 billion to $439 billion and its annual costs by 

$24 billion to $28 billion. Total production costs would be nearly triple what DoD is currently planning to 

spend on production over the next few decades.

• Although some of those strategies would require the production of additional warheads, those estimates do not 

include additional costs for the Department of Energy to produce more warheads. The estimates also exclude 

costs for DoD to establish new operating bases and training facilities, if necessary, or to expand production 

capability for delivery vehicles and the platforms that carry them (to accelerate production if that is desired). 

Costs, therefore, would probably be higher—in some cases, considerably so—than CBO estimates. 

• Expanding its forces could take the United States many years. Available warheads could be uploaded relatively 

quickly, but additional delivery systems and warheads would probably not be available before the late 2030s or 

early 2040s. Most of the additional costs of expanding forces would thus occur a few decades from now.

www.cbo.gov/publication/56475
Contents

Summary 1

What Could Happen If New START Expired? 1

How Did CBO Analyze the Issue? 1

What Did CBO Find? 2

What Costs Were Excluded From This Analysis? 4

Background on the Treaty and Arguments For and Against Its Extension 4

Arguments Against Extension 5

Arguments For Extension 6

Possible U.S. Responses to New START’s Expiration 6

Maintain the Status Quo 7

Expand U.S. Intelligence Capabilities 7

Expand Missile Defenses 8

Expand Conventional Missile Forces 8

Expand Nonstrategic Nuclear Forces 9

Strategic Nuclear Forces and Broad Approaches for Their Expansion 9

Current and Planned Nuclear Forces 10

Expansion by Uploading Additional Warheads 10

Expansion by Fielding Additional Delivery Vehicles 12

Costs of Producing New Nuclear Systems 13

Costs of Purchasing Additional Delivery Vehicles 13

Costs of Producing New Warheads 14

Costs of Expanding Strategic Nuclear Forces to the Limits Under Previous Treaties 15

CBO’s Approach 15

BOX 1. COUNTING RULES USED IN THIS ANALYSIS 16

Costs of Expanding Forces to Moscow Treaty Limits 17

Costs of Expanding Forces to START II Treaty Limits 17

Costs of Expanding Forces to START I Treaty Limits 19

List of Tables and Figures 21

About This Document 22
Notes

Unless this report indicates otherwise, all years referred to are federal fiscal years, 

which run from October 1 to September 30 and are designated by the calendar year 

in which they end.

Numbers in the text and tables may not add up to totals because of rounding. 

In this report, “cost” refers to budget authority, the amount that would need to be 

appropriated to implement the Administration’s plans. All costs are in fiscal year 

2020 dollars.

On the cover (clockwise from upper left): an Ohio class submarine, a B-52 bomber, a 

Minuteman III intercontinental ballistic missile, and a B-2 bomber.
The Potential Costs of Expanding U.S. Strategic 

Nuclear Forces If the New START Treaty Expires

Summary

The New Strategic Arms Reduction Treaty (New 

START) between the United States and Russia will 

expire in February 2021 unless both parties agree to an 

extension, which could last for up to five years. That 

treaty places limits on the number of deployed strategic 

nuclear warheads (1,550) and delivery systems (800 

missile launchers and bombers, 700 of which may be 

deployed at any given time) that each country may field. 

How and when the United States or Russia would 

respond to the expiration of New START is unclear. To 

help policymakers understand the budgetary implications of one potential course of action the United States 

could take, the Congressional Budget Office was asked 

to examine the potential costs that the Department of 

Defense (DoD) might incur if the United States chose 

to increase its strategic nuclear forces to levels that are 

roughly consistent with the limits under three earlier 

arms control treaties. 

What Could Happen If New START Expired?

If the New START treaty was allowed to expire, the size 

of the nuclear arsenals of the United States and Russia 

would be without limits for the first time in decades. 

The transparency and confidence-building procedures 

included in New START and previous treaties would 

cease, in which case both parties would lose the means to 

have direct knowledge of their adversary’s capabilities. In 

the absence of on-site inspections, data exchanges, and 

limits on the encryption of flight text data, uncertainty 

about each other’s forces would grow over time. 

Many responses to the end of strategic nuclear arms 

control would be possible, including some that would 

not affect the size of strategic nuclear forces. For example, uncertainty about the other party’s forces might lead 

the United States to expand its intelligence capabilities 

or to hedge against uncertainty about the other party’s 

intentions by expanding missile defenses. Conversely, the 

United States might choose to emphasize conventional 

deterrence by expanding its conventional missile forces 

or to increase its capabilities for regional conflict by 

expanding nonstrategic nuclear forces.

In terms of strategic nuclear forces, many different 

responses also are possible. Each party might opt to 

make no changes to its current plans for nuclear forces 

for many years. Or one party might choose to expand its 

forces, either to seek an advantage or because, without 

the ability to inspect the other’s forces, it was concerned 

that the other is building up its arsenal and wants to 

hedge against that uncertainty. Or both parties might 

choose to expand their forces, perhaps significantly. The 

lack of constraints on ballistic missile defenses could 

further complicate that dynamic. (The United States 

withdrew from the ABM Treaty, which limited the number and locations of Russian and U.S. defenses against 

long-range missiles, in 2002.)

How Did CBO Analyze the Issue?

CBO was asked to estimate the costs of increasing 

deployed U.S. strategic nuclear forces to the levels specified in three previous arms control treaties: the Moscow 

Treaty (1,700 to 2,200 warheads), the START II treaty 

(3,000 to 3,500 warheads), and the START I treaty 

(6,000 warheads). Although each treaty had a different 

protocol for counting warheads, for this analysis CBO 

used the rules for the Moscow Treaty because they most 

closely reflect the number of nuclear weapons actually 

deployed.

The United States could field a wide variety of force 

structures, each with very different costs, to reach 

those levels. To illustrate both ends of the distribution 

of potential forces and their associated costs, CBO 

examined two approaches for expanding forces at each 

warhead level.

• A lower-cost and less flexible approach would increase 

the number of warheads allocated to each missile and 

bomber to, or near to, its maximum (an approach 
2 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

known as uploading) and minimize the number of 

additional delivery systems purchased, if any.

• A more flexible and higher-cost approach would 

purchase enough delivery systems to reach the desired 

total numbers of warheads while maintaining (as 

nearly as possible) the current number of warheads 

allocated to each missile and bomber. 

DoD also could choose to field a force that lies between 

those two approaches. To estimate costs, CBO used 

methods from its previous work on nuclear forces.1

1. See Congressional Budget Office, Approaches for Managing the 

Costs of U.S. Nuclear Forces, 2017 to 2046 (October 2017), 

www.cbo.gov/publication/53211. 

What Did CBO Find?

If the New START treaty expired, the United States 

could choose to make no changes to its current plans for 

nuclear forces, in which case it would incur no additional 

costs. If the United States chose to increase its forces in 

response to the expiration of the treaty, modest expansions could be relatively inexpensive and could be done 

quickly. Larger expansions could be quite costly, however, and could take several decades to accomplish (see 

Table 1). Accelerating production of additional forces 

would probably have only a small effect on that timeline 

and could increase costs.

• Expanding forces to the Moscow Treaty limits would 

have no effect on DoD’s costs, because current and 

Table 1.

Approaches for Fielding Nuclear Warheads at Selected Treaty Limits

Additional Costs for DoD

(Billions of 2020 dollars)

Approach Description

Total Number of 

SDVs

One-Time 

Acquisition Costs

Annual Operation 

and Sustainment 

Costs

Moscow Treaty

No Change 

From Current 

Plans

Keep the plans for current-generation and 

next-generation forces as they are

As planned 0 0

START II

Lower Cost

(Upload only)

Reach START II levels with currrent-generation or planned nextgeneration forces by uploading ICBMs and SLBMs to highest levelsAs planned 0.1 0

More Flexible Expand next-generation forces to 3,000 warheads at current SLBM 

and ICBM warhead loadings

1,004 to 1,221 114 to 172 3 to 8

START I

Lower Cost Expand next-generation forces to 6,000 warheads by 

uploading warheads to high levels; purchase sufficient new SDVs

1,043 to 1,359 88 to 149 4 to 10

More Flexible Expand next-generation forces to 6,000 warheads at 

current ICBM loadings; purchase sufficient new SDVs to 

reach limit of 1,600

1,544 to 1,600 410 to 439 24 to 28

Source: Congressional Budget Office.

Costs are for production of delivery systems only and do not include research and development costs or the Department of Energy’s costs to produce, 

sustain, or store more nuclear warheads (if necessary).

The lower-cost approach would increase the number of warheads on delivery systems (known as uploading) and minimize the number of additional 

delivery systems; the more flexible approach would purchase additional delivery systems to reach the desired warhead levels, preserving as much as 

possible the flexibility provided by today’s smaller number of warheads on each delivery vehicle. Other approaches to expand forces would lie between 

those two approaches.

Under the Moscow Treaty, warheads are limited to 1,700 to 2,000, and there are no limits on SDVs (ballistic missiles and bombers). Under START II, 

warheads are limited to 3,000 to 3,500, and there are no limits on SDVs. Under START I, warheads are limited to 6,000 and SDVs to 1,600. 

DoD = Department of Defense; ICBM = intercontinental ballistic missile; SDV = strategic delivery vehicle; SLBM = submarine-launched ballistic missile; 

START = Strategic Arms Reduction Treaty.
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 3

planned next-generation forces are both already at 

those limits.

• Expanding forces to START II limits could be 

relatively inexpensive if DoD used a lower-cost 

approach that involved uploading warheads only: 

about $100 million in onetime costs for DoD (with 

no additional ongoing operation and sustainment 

costs) for both current and next-generation forces, 

CBO estimates. If DoD used a more flexible 

approach that involved purchasing enough delivery 

systems to maintain current warhead loading levels, 

that expansion would be much more expensive, 

eventually totaling $114 billion to $172 billion in 

acquisition costs over several decades and $3 billion 

to $8 billion in additional annual costs after the 

expanded forces were in place. The additional costs 

of expanding to START II limits under the more 

flexible approach would lead to total production costs 

roughly 50 percent higher than currently planned (see 

Figure 1). 

• Expanding forces to START I limits would require 

even more new delivery systems and warheads. 

Under a lower-cost approach that minimized the 

number of additional delivery systems, DoD would 

incur onetime costs of $88 billion to $149 billion 

over several decades to buy additional delivery 

vehicles and $4 billion to $10 billion in additional 

operation and sustainment costs each year, in CBO’s 

estimation. Under a more flexible approach that 

maintained as much as possible the current number 

of warheads loaded on missiles and allocated to 

bombers by having DoD purchase enough delivery 

systems, CBO estimates that DoD would incur 

onetime costs eventually totaling $410 billion to 

$439 billion to purchase additional systems as well 

as additional annual operation and sustainment costs 

(beyond those for planned forces) of $24 billion to 

$28 billion after the expanded forces were in place. 

The additional costs of expanding to START I limits 

under the more flexible approach would lead to 

Figure 1.

Estimated Total DoD Production Costs for Planned Next-Generation Nuclear Forces and 

Expanded Nuclear Forces at Different Force Levels

Billions of Fiscal Year 2020 Dollars

START II

Level

START I

Level

0 100 200 300 400 500 600 700 800

Lower-Cost

Approach

Other

Approaches

More Flexible

Approach

Planned Forces

and Moscow

Treaty Forcesa

Under the more flexible 

approach, the additional 

costs of expanding to START 

II limits would lead to total 

production costs roughly 

50 percent higher than 

those currently planned. 

For START I, the costs would 

be nearly three times those 

currently planned.

Source: Congressional Budget Office.

DoD = Department of Defense; START = Strategic Arms Reduction Treaty.

Costs are for production of delivery systems only and do not include research and development costs or the Department of Energy’s costs to produce, 

sustain, or store more nuclear warheads (if necessary). 

The lower-cost approach would increase the number of warheads and minimize the number of additional delivery systems; the more flexible approach 

would purchase additional delivery systems to reach the desired number of warheads, preserving as much as possible the flexibility provided by 

today’s smaller number of warheads on each delivery vehicle. Other approaches to expand forces would lie between those two approaches.

a. Current and planned next-generation forces are both already at Moscow Treaty limits, so there would be no additional costs.
4 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

production costs nearly three times those currently 

planned (see Figure 1).

For comparison, the costs to produce the currently 

planned quantities of next-generation delivery systems 

is about $240 billion, CBO estimates, not including 

development costs. 

What Costs Were Excluded From This Analysis?

The figures cited in this report do not include the 

Department of Energy’s (DOE’s) costs of producing or 

maintaining additional warheads. Most information 

about the nuclear stockpile is classified, so it is difficult to determine whether and how many additional 

warheads would be needed and thus what additional 

funding would be required. Those costs could be considerable, though, for all but modest increases in forces.

CBO’s estimates also exclude DoD’s costs of establishing 

new operating bases and training facilities (if needed) 

and DoD’s costs of expanding production capability 

for delivery systems (if needed because production 

is accelerated). CBO also excluded the costs of other 

actions that the United States might take if New START 

expired without another agreement in place, including 

expanding U.S. intelligence capabilities, strengthening 

missile defenses, increasing long-range conventional (that 

is, nonnuclear) missile forces, or expanding short-range 

nuclear forces.

Background on the Treaty and 

Arguments For and Against Its Extension

The New START treaty is the latest in a series of strategic nuclear arms control treaties—following START I, 

START II, and the Moscow Treaty—between the United 

States and Russia (or the Soviet Union).2

 Those four 

treaties, which together span more than 25 years of continuous coverage, placed increasingly stringent limits on 

the size (and sometimes the capability) of each country’s 

2. The four most recent U.S.–Russian nuclear strategic arms control 

agreements are (in chronological order): the Treaty on the 

Reduction and Limitation of Strategic Offensive Arms (known 

as START I); the START II treaty, which was signed by the U.S. 

and Russian presidents but was never fully ratified and never 

entered into force; the Strategic Offensive Reductions Treaty (or 

the Moscow Treaty); and the Treaty on Measures for the Further 

Reduction and Limitation of Strategic Offensive Arms (known 

as the New Strategic Arms Reduction Treaty, or New START). 

For details on those agreements, see Amy F. Woolf, Paul K. Kerr, 

and Mary Beth D. Nikitin, Arms Control and Nonproliferation: A 

Catalog of Treaties and Agreements, Report for Congress RL33865 

(Congressional Research Service, updated March 26, 2020).

strategic nuclear arsenal (see Table 2).3 The New START 

treaty limits each country to 800 total deployed and 

nondeployed strategic delivery vehicles (SDVs) and missile launchers, 700 deployed SDVs, and 1,550 deployed 

warheads. Those limits represent about a 50 percent 

decrease in “accountable” (counting toward the total) 

SDVs and a 75 percent decrease in accountable warheads 

from the limits in the START I treaty (although the 

rules for counting warheads differed markedly between 

the two treaties). The New START treaty will expire in 

February 2021 unless both Russia and the United States 

agree to extend it for up to five years.

In addition to placing limits on the size of strategic 

nuclear forces, the New START treaty (like the others 

before it) provides extensive verification, data exchange, 

and confidence-building measures that allow each party 

insight into the other’s capabilities. In New START, 

those measures include the following: 

• Up to 18 on-site inspections each year (and the right 

to verify the number of warheads on an SDV of the 

inspector’s choice); 

• Biannual declarations of the total number of SDVs, 

the number of warheads on each type of SDV, and 

the bases where they are located; 

• Notification whenever the status of any SDV changes 

(if it switches from deployed to not deployed, for 

example, or if it is relocated to a different base); and 

• A pledge to not interfere with the other party’s 

national technical means (which primarily refers to 

satellite imagery and electronic signals collection 

during testing), including not concealing SDVs from 

satellite observation.

Whether the New START treaty should be extended 

has been the subject of debate. Administration officials 

have said that the United States would prefer to pursue a 

new trilateral treaty that would include both Russia and 

China.4

 Statements from Russian officials have generally 

3. Nuclear weapons are referred to as strategic if the delivery system 

(ground-launched missile, submarine-launched missile, or 

bomber) is capable of delivering them over long ranges, typically 

3,000 miles or more. Nuclear weapons that are deliverable over 

shorter ranges are referred to as nonstrategic, or tactical, weapons.

4. See Department of State, Office of the Spokesperson, “Briefing 

With Senior State Department Official on the New START” 

(March 9, 2020), https://go.usa.gov/xwt94. 
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 5

supported the extension of New START.5 China has 

stated that it has “no intention to participate” in trilateral 

arms control negotiations.6

Arguments Against Extension 

Opponents of extending the treaty often cite a history 

of Russian violations of other treaties as a reason to not 

extend this one. Other arguments against extension are 

centered on shortcomings of the New START treaty: 

5. See Ankit Panda, “Putin: Russia Ready to Extend New START 

With U.S. ‘Without Any Preconditions,’” The Diplomat

(December 6, 2019), https://tinyurl.com/ycbpssyn.

6. See Agence France-Presse, “China Says It Has ‘No Intention’ of 

Joining Arms Talks With U.S. and Russia,” South China Morning 

Post (January 22, 2020), https://tinyurl.com/y7je8o8g. 

Opponents contend that even though the treaty may 

have met U.S. and allied national security requirements 

in 2010, it no longer does because it does not cover 

new developments, including growth in the number of 

Russian shorter-range nuclear weapons capable of striking North Atlantic Treaty Organization (NATO) allies 

of the United States.7

 (New START places no limits on 

nonstrategic nuclear weapons, of which Russia has substantially more than the United States.) 

In addition, opponents argue that the treaty does not 

cover new exotic systems that Russia has developed while 

7. See Eric Edelman and Franklin C. Miller, “Russia Is Beefing Up 

Its Nuclear Arsenal; Here’s What the U.S. Needs to Do,” Politico

(December 31, 2019), https://tinyurl.com/sgej9z6. 

Table 2.

Details of Recent Strategic Arms Control Treaties

New START Moscow (SORT) START IIa START I

Timeline

Entry Into Force 2011 2003 n.a. 1994

Deadline to Meet Limits 2018 2012 n.a. 2001

Expiration 2021 2011b n.a. 2009

Limits on Forces

Number of Strategic Delivery 

Vehicles

800 n.a. n.a. 1,600

Number of Deployed Strategic 

Delivery Vehicles

700 n.a. n.a. n.a.

Number of Warheads 1,550 1,700 to 2,200 3,000 to 3,500 6,000

Warhead Counting Rules

Description Deployed bombers count as 

1 warhead each; deployed 

ICBMs and SLBMs count as 

the actual number of war- heads deployed rather than 

a fixed maximum value

No counting rules described 

in the treaty's text; the 

United States informed 

Russian negotiators it would 

use actual deployed warheads on ICBMs and SLBMs 

and bomber weapons 

deployed on bombers or 

stored at bomber bases

Phased out bomber discounts from START I (see 

the next panel) but allowed 

ICBMs and SLBMs to count 

as fewer than the maximum 

under some conditions

Warhead count set to the 

maximum number tested 

on each platform, except 

the first 150 bombers that 

carry cruise missiles were 

discounted to count as 10 

warheads each (compared 

with 20 maximum on the 

B-52); bombers that carry 

only bombs count as 

1 warhead each

Warheads on Current Forces 

as Calculated Using Each 

Treaty's Counting Rules

1,467 1,962 2,760 3,920

Source: Congressional Budget Office, using information from the Department of State, the Nuclear Threat Initiative, and the Arms Control Association.

ICBM = intercontinental ballistic missile; SLBM = submarine-launched ballistic missile; SORT = Strategic Offensive Reductions Treaty; START = Strategic 

Arms Reduction Treaty; n.a. = not applicable.

a. The START II treaty was negotiated and signed, but it was never fully ratified and never entered into force. Both sides largely complied with its terms, 

however.

b. The Moscow treaty was not scheduled to expire until 2012. However, it was superseded by New START when that treaty went into effect.
6 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

New START has been in force and, given the bilateral 

nature of the treaty, places no constraints on China’s 

expanding nuclear forces. Those analysts often argue that 

there is no rush to extend the treaty and that holding 

out on extension could be used as leverage to negotiate 

improvements to the existing agreement or perhaps a 

new trilateral agreement that includes China.8

 Other 

critics argue that Russia uses arms control as a tool for 

competition by locking in advantages through the terms 

of the treaty.9

 One analysis asserts that New START’s 

approach of counting the actual number of deployed 

warheads and disregarding the potential for loading 

more warheads on SDVs has positioned Russia to be 

able to expand its forces much more rapidly than the 

United States. That conclusion is based on assertions that 

Russia’s intercontinental ballistic missiles (ICBMs) have 

the capacity to carry many more warheads than they do 

currently and that Russia has the ability to manufacture 

thousands of new warheads each year.10

Arguments For Extension 

Proponents of extending the treaty offer counterarguments. They contend that Russia has consistently 

complied with the New START treaty (despite violating 

some earlier treaties). Proponents also argue that engaging China in arms control talks is a worthwhile goal but 

will be difficult and that extending New START would 

provide “a necessary foundation from which to pursue 

more ambitious arms control talks.”11 Moreover, extending New START would provide time for what would 

probably be long and extensive negotiations for a multilateral arms control agreement or for making changes 

to New START. For example, including nonstrategic 

weapons in a modified New START or a new bilateral 

agreement would take time because Russia would probably ask for limits on U.S. missile defenses in return.12

8. See Rebecca L. Heinrichs, “Automatically Extending New 

START Will Not Increase Stability,” Real Clear Defense

(February 28, 2020), https://tinyurl.com/yak99rrq. 

9. See Thomas G. Mahnken, Forging the Tools of 21st Century Great 

Power Competition (Center for Strategic and Budgetary Analysis, 

2020).

10. See Mark B. Schneider, “Russian Nuclear Force Expansion and 

the Failure of Arms Control,” Real Clear Defense (October 29, 

2019), https://tinyurl.com/y7ldmfa8. 

11. See Kingston Reif, Responses to Common Criticisms About 

Extending New START, Arms Control Association Issue Brief, 

vol. 12, no. 1 (February 5, 2020), https://tinyurl.com/ybuhx3fk. 

12. See Frank A. Rose, Brookings Institution, “Deterrence, 

Modernization, and Alliance Cohesion: The Case for Extending 

Additionally, proponents point out that, as a signatory 

to the international Non-Proliferation Treaty, the United 

States, along with all nations possessing nuclear weapons, 

is obligated to pursue reductions in its nuclear arsenal.13

One analysis that assessed the military implications of 

the expiration of New START concluded that the United 

States would lose insight into Russian forces that was 

provided by on-site inspections; that loss, in turn, would 

probably lead to increased costs associated with expanding intelligence capabilities or personnel and would also 

probably lead to a costly expansion of planned U.S. 

nuclear modernization programs.14 That analysis argued 

that Russia has the ability to upload and produce more 

warheads quickly, which would enable that country to 

expand its strategic nuclear forces at a faster rate than 

the United States could (at least initially). That potential 

Russian advantage is a reason to extend New START, 

according to proponents, not to let it expire. 

Possible U.S. Responses to New START’s 

Expiration

The United States might keep its current plans for 

nuclear forces unchanged, even if it decides not to renew 

New START. According to public reports from shortly 

after the New START treaty went into force, DoD 

concluded that Russia “would not be able to achieve a 

militarily significant advantage by any plausible expansion of its strategic nuclear forces, even in a cheating or 

breakout scenario under the New START Treaty, primarily because of the inherent survivability of the planned 

U.S. strategic force structure, particularly the Ohio class 

ballistic missile submarines, a number of which are at sea 

at any given time.”15 The United States might conclude 

that that assessment is still valid even if New START has 

expired.

Whether the United States chose to increase its nuclear 

forces might depend on the circumstances. For example, 

New START With Russia,” Order From Chaos (blog entry, 

January 16, 2020), https://tinyurl.com/ycmszay5. 

13. See Thomas Countryman, “Russia, China, Arms Control, 

and the Value of New START,” Arms Control Today

(November 2019), https://tinyurl.com/yanfmw3n. 

14. See Frank G. Klotz, The Military Case for Extending the New 

START Agreement (RAND Corporation, February 2020), 

www.rand.org/pubs/perspectives/PE350.html.

15. See Department of Defense, as cited in Hans Kristensen, 

Federation of American Scientists, “DoD: Strategic 

Stability Not Threatened Even by Greater Russian Nuclear 

Forces,” Strategic Security Blog (October 10, 2012) 

https://fas.org/blogs/security/2012/10/strategicstability/.
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 7

if Russia uploaded warheads onto its ICBMs but did not 

increase the number of ICBMs, the United States might 

opt not to act, if the current U.S. force was deemed adequate to cover the assigned targets. If Russia’s uploading 

of warheads passed a certain point, however, a decision might be made that too large a Russian numerical 

advantage would cause foreign policy problems. In that 

case, even if the United States still felt there was no military reason to expand its force, it might do so to avoid 

problems that could affect crisis management, unnerve 

U.S. allies, or embolden Russian leaders to threaten use 

of nuclear weapons. In another case, if neither Russia nor 

the United States increased their forces after the treaty’s 

expiration but China did, either Moscow or Washington 

(or both) might decide that additional nuclear forces 

were needed. 

A U.S. response, should one occur, could happen soon 

after the treaty expired or in later years. If the treaty was 

not extended, the resulting lack of transparency and 

on-site inspections over time could lead to increasing 

U.S. uncertainty about Russian forces and could create 

pressure to act. As a hedge against that uncertainty, U.S. 

planners might decide to expand strategic nuclear forces. 

Such an expansion could occur in a number of ways. 

CBO was asked to analyze a range of potential costs that 

might be incurred if forces were expanded to levels consistent with the limits established under three previous 

arms control treaties (see Table 2 on page 5).

In addition to expanding strategic nuclear forces (or 

instead of doing so), the United States could take other 

actions if the treaty was not extended: It could expand its 

intelligence capabilities, for instance, or it could expand 

its missile defenses, conventional forces, or nonstrategic 

nuclear forces (that is, nuclear weapons that are delivered 

by shorter-range systems, like certain tactical aircraft). 

Those actions could be spurred by a real or perceived 

expansion of Russian forces, concern about uncertainty 

of the state of Russian nuclear forces in the absence of 

verification, or some other stimulus. Taking any of those 

actions (or, as is more likely to occur, taking a combination of two or more of them, possibly in addition to 

expanding strategic nuclear forces) could impose costs on 

the United States. CBO has not estimated those costs, 

however, given the significant uncertainty about what 

actions might be taken and to what extent.

Maintain the Status Quo

The United States could decide that its forces, as currently planned, are appropriate and sufficient for the 

geopolitical environment, even in the absence of treaties that constrain strategic nuclear forces and permit 

inspections and other transparency measures. Current 

plans already call for the development of new technologies in several areas (some of which are described below) 

to respond to advances in the capabilities of potential 

adversaries. 

Not expanding U.S. strategic nuclear forces in response 

to an expansion of Russian strategic nuclear forces would 

represent a change in U.S. strategy. Historically, the 

United States has generally pursued a deterrence strategy 

that features elements of both punishment and denial to 

varying degrees. According to that strategy, the best way 

to avoid nuclear war is to deny the adversary any plausible notion of victory, however it defines victory, at any 

level of nuclear conflict, from limited strikes through an 

all-out nuclear exchange.16 That strategy could change 

for a number of reasons, however, including a decision to 

fund other defense priorities instead. 

Hewing to the status quo would not increase DoD’s costs 

beyond those it expects to incur for currently planned 

programs.

Expand U.S. Intelligence Capabilities

The United States fields a variety of satellites, both 

classified and unclassified, to collect intelligence about 

adversaries through high-resolution imagery, infrared 

detection of missile launches, interception of electromagnetic communication, and other methods. Without 

insight into Russian strategic forces from on-site inspections and other transparency measures provided by a 

treaty, the United States would probably need to rely 

more heavily on satellite intelligence; moreover, it might 

feel the need to increase the number of satellites in orbit 

or purchase more commercial satellite imagery (or both) 

and bolster its capabilities to analyze intelligence data.17

Those approaches are not without risk, however. The 

New START treaty, like the treaties that preceded it, prohibits interference with the other party’s national technical means (a catchall term for intelligence and national 

security satellites and other means to verify treaty compliance). If that prohibition expired, U.S. satellites would 

16. For more details, see Congressional Budget Office, Approaches for 

Managing the Costs of U.S. Nuclear Forces, 2017 to 2046 (October 

2017), pp. 24–25, www.cbo.gov/publication/53211.

17. For a more detailed discussion of the consequences of the lack of 

transparency into Russian forces, see Vince Manzo, Nuclear Arms 

Control Without a Treaty? Risks and Options After New START, 

Deterrence and Arms Control Paper no. 1 (CNA Corporation, 

March 2019), pp. 38–49, www.cna.org/research/NAC.
8 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

be at risk of interference ranging from performance 

degradation (through jamming or other techniques) to 

destruction from a direct attack.18

If the United States decided to replace or augment its 

intelligence systems, the costs could be sizable. Highcapability satellites can be expensive—for example, 

producing the fifth and sixth geostationary satellites 

in the Space-Based Infrared Satellite-High system, an 

unclassified missile launch detection constellation, cost 

an average of about $1.1 billion each (in 2020 dollars). 

Because it is unclear what steps, if any, the United States 

would take to compensate for the loss of monitoring and 

transparency measures that would have been provided 

under New START, CBO did not estimate those costs.

Expand Missile Defenses

The United States could strengthen its defenses against 

long-range ballistic missiles if it concluded that the risk 

of a nuclear attack from Russia had increased or that 

stronger defenses would be prudent in the face of uncertainty about the state of Russian nuclear forces. Such an 

expansion in missile defenses would constitute a significant policy change, however. Previous statements of U.S. 

missile defense policy, including the 2019 Missile Defense 

Review, have held that missile defenses of the homeland 

were intended to counter long-range missile attacks from 

rogue states and that nuclear deterrence was intended to 

address the nuclear threat from Russia and China. 

Currently, U.S. missile defense comes primarily from 

the Ground-Based Midcourse Defense (GMD) system, 

which comprises silo-based long-range interceptor missiles in Alaska and California, supported by an array of 

radars around the world. That system is complemented 

by Aegis Ballistic Missile Defense interceptors based both 

on ships and at ground sites; a test is slated for later this 

year to determine the efficacy of Aegis against ICBMs. 

The 2019 Missile Defense Review stated that GMD could 

be expanded by building new silos at the Alaska base if 

“emerging threat conditions” suggested they were needed.19

18. See Theresa Hitchens, “End of New START Could Risk U.S. 

Sats: Aerospace Corp.,” Breaking Defense (January 15, 2020), 

https://tinyurl.com/yassuhrk. 

19. See Department of Defense, Missile Defense Review (January 

2019), p. XVI, https://go.usa.gov/xwtmx (PDF, 26.6 MB). 

Building 40 new silos at the Alaska GMD base and 

purchasing interceptors for them would cost about 

$5 billion, CBO estimates. That amount is very uncertain, though, because the GMD program is in the early 

stages of a complete redesign.20 The United States also 

could choose to expand or accelerate the development of 

other missile defense systems, including those designed 

to counter new hypersonic weapons (described in the 

next section), which would result in additional costs.

Expand Conventional Missile Forces

The United States could choose to increase its conventional (that is, nonnuclear) capabilities to strengthen 

deterrence, if an expansion was deemed necessary to 

respond to an unconstrained Russian strategic nuclear 

force. One way to do that would be to accelerate or 

otherwise expand development programs for hypersonic 

weapons or conventional intermediate-range ballistic 

missiles (IRBMs). Both of those types of weapons are 

already under development for conventional missions 

to counter Russia’s and China’s antiaccess strategies.21

Those weapons also could be designed to perform some 

missions that in the past might have required nuclear 

weapons, like striking high-value or hardened targets at 

long range on short notice. 

Hypersonic weapons have three salient characteristics, all 

of which give them advantages over other weapons and 

make them difficult to defend against: 

• They can travel at least five times the speed of sound 

(or Mach 5, which is equivalent to about 3,800 miles 

per hour or 1.7 kilometers, or km, per second) for at 

least part of their trajectory; 

• They spend a significant fraction of their trajectory 

(the midcourse phase) flying through the upper 

atmosphere and use the atmosphere to provide lift; 

and 

20. See Congressional Budget Office, Assessing the Cost of 

the Recommendations of the 2019 Missile Defense Review

(forthcoming).

21. Antiaccess strategies are actions that would impede the 

deployment of U.S. forces into the combat theater, limit the 

locations from which those forces could effectively operate, or 

force them to operate from locations farther from the locus of 

conflict than they would normally prefer. See Roger Cliff and 

others, Entering the Dragon’s Lair: Chinese Antiaccess Strategies and 

Their Implications for the United States (RAND, 2007).
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 9

• They have the ability to maneuver to avoid enemy 

defenses in the midcourse phase. 

Several U.S. programs are seeking to develop hypersonic 

weapons, including hypersonic glide weapons (which 

are launched with a rocket booster and then use aerodynamic lift to maneuver and to extend their range). 

At least one program is developing a hypersonic cruise 

missile (which is launched with a rocket booster to gain 

enough speed to enable it to use an exotic engine called 

a scramjet to reach hypersonic speeds). Some of those 

programs have begun flight-testing their prototypes. 

The United States also could choose to accelerate 

or expand its development and fielding of groundlaunched IRBMs now that it is no longer constrained 

by the Intermediate-Range Nuclear Forces treaty. That 

treaty barred the United States and Russia from possessing ground-launched cruise or ballistic missiles with 

ranges between 500 km and 5,500 km (or 300 miles to 

3,400 miles). Citing an ongoing Russian violation of 

the treaty, the United States recently withdrew from it. 

Currently, at least one program is working on developing 

a conventionally armed IRBM. 

Programs to develop hypersonic and IRBM weapons are 

in the early stages, so their development and production 

costs are not yet known. For that reason, CBO did not 

estimate those costs. 

Expand Nonstrategic Nuclear Forces

The United States currently fields only one type of 

nonstrategic nuclear weapon, the B61 bomb, which 

is carried by F-15E tactical aircraft as well as NATO 

allies’ aircraft.22 According to one report, about 150 of 

those bombs are based in Europe in support of NATO, 

and some are stored in the United States.23 Unclassified 

sources estimate that Russia, by comparison, maintains a 

substantially larger stockpile of about 1,800 nonstrategic 

22. There are several versions of the B61 bomb. Some are carried 

by tactical aircraft for nonstrategic missions, whereas others are 

carried by B-2 bombers for strategic missions. The Department of 

Energy’s B61-12 life-extension program, which is currently in the 

design phase, will combine the current types into a single version 

that can perform both strategic and nonstrategic missions.

23. Those bombs also can be carried by NATO partners’ 

aircraft. See Hans M. Kristensen and Matt Korda, “United 

States Nuclear Forces, 2020,” Bulletin of the Atomic 

Scientists (January 2020), https://thebulletin.org/2020/01/

united-states-nuclear-forces-2020/. 

warheads that can be delivered by several different 

vehicles.24

Citing Russia’s advantage in the number and types 

of nonstrategic nuclear weapons it fields, the most 

recent Nuclear Posture Review (NPR), released in 

January 2018, called for putting the United States on a 

path to expand its nonstrategic nuclear forces by developing and fielding a new nuclear-armed, sea-launched 

cruise missile (SLCM). DoD is analyzing alternatives to 

determine the concept for the SLCM. 

In 2019, CBO estimated that the cost of fielding a 

SLCM would be about $9 billion (in current dollars). 

CBO assumed that the design of the SLCM would draw 

heavily from the Long-Range Standoff (LRSO) weapon, 

a nuclear-armed, air-launched cruise missile now in 

development.25 (CBO’s estimate did not include the 

costs to integrate the SLCMs onto the ships selected to 

carry them or associated costs like nuclear-specific training, weapon storage, or security.) 

If the United States felt that conditions warranted additional expansion of nonstrategic nuclear forces, it could 

develop nuclear warheads for hypersonic missiles or 

IRBMs (discussed in the previous section) or add nuclear 

capability to one of the Navy’s tactical aircraft. Those 

approaches would incur additional costs; operation costs 

for training, weapon storage, and security could be substantial, particularly if nuclear weapons were deployed on 

platforms that do not currently carry them.

Strategic Nuclear Forces and 

Broad Approaches for Their Expansion

The Department of Defense operates a strategic nuclear 

force that complies with the limits specified in the New 

START treaty (up to 1,550 warheads and 800 delivery vehicles and missile launchers, 700 of which can 

be deployed). Those forces are aging, so DoD has 

started replacing them—a process that will continue 

over the next few decades. If the United States decided 

to expand its strategic nuclear forces, DoD could do 

so in two ways: by uploading warheads on currently 

24. See Hans M. Kristensen and Matt Korda, “Russian Nuclear 

Forces, 2020,” Bulletin of the Atomic Scientists (March 2020), 

https://thebulletin.org/2020/03/russian-nuclear-forces-2020/. 

25. See Congressional Budget Office, Projected Costs of U.S. Nuclear 

Forces, 2019 to 2028 (January 2019), p. 4, www.cbo.gov/

publication/54914.
10 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

fielded delivery systems or by fielding additional delivery systems. Any substantial expansion of U.S. forces in 

response to a real or perceived Russian buildup would 

probably include a combination of the two.

To develop the approaches used in this analysis, which 

would increase nuclear forces to the limits set in previous 

treaties, CBO considered force structures comprising 

either currently deployed systems or next-generation 

systems that are being developed to replace the currentgeneration systems. Reconstituting nuclear forces as 

they had been deployed (or had planned to be deployed) 

when the previous treaties were in force is not possible. Many of the systems that were in service then have 

been out of production for decades and have since been 

retired, have had their inventory substantially reduced, or 

have been converted to serve only nonnuclear roles.

Current and Planned Nuclear Forces

For many years, U.S. strategic nuclear forces have been 

made up of three components: intercontinental ballistic 

missiles, ballistic missile submarines (SSBNs) carrying long-range submarine-launched ballistic missiles 

(SLBMs), and long-range bombers carrying nuclear 

bombs or nuclear-armed cruise missiles; together, 

those forces are commonly referred to as the triad. The 

Department of Defense currently fields these systems:

• Ohio class SSBNs that are configured to carry 

20 D5 SLBMs, 

• Silo-based Minuteman III ICBMs, 

• B-52H bombers that carry Air-Launched Cruise 

Missiles (ALCMs), and 

• B-2A bombers that carry B61 and B83 bombs. (For 

quantities and other details for all of those systems, 

see Table 3, top panel).

Nearly all of those systems are nearing the end of their 

operational life, and many have undergone one or more 

life-extension programs (LEPs). Over the past decade, 

DoD has been designing replacements for those systems, 

most of which are slated to enter production over the 

next five years or so. The next-generation systems will 

comprise the following:

• Columbia class SSBNs carrying 16 existing D5 

SLBMs and, eventually, newly constructed SLBMs 

using an updated design of the D5 missile, 

• Ground-Based Strategic Deterrent (GBSD) ICBMs 

in refurbished Minuteman III silos, 

• B-52H bombers with new engines and other 

refurbishments carrying LRSO cruise missiles, and 

• New B-21 bombers, which will be capable of carrying 

both B61 nuclear bombs and LRSOs. (For details, see 

Table 3, bottom panel).26

At planned rates of production, those new systems will 

not be fully in place until the early 2040s.

As configured, current- and next-generation forces 

comply with New START’s limits on delivery systems 

and deployed warheads, according to the definitions and 

counting rules laid out in that treaty. The rules with the 

greatest impact are those that affect how warheads are 

counted: Deployed ICBMs and SLBMs count as the 

actual number of warheads they carry, whereas deployed 

bombers count for only a single warhead each (regardless of how many warheads they carry). To meet the 

1,550-warhead limit, therefore, current forces carry an 

average of 4.2 warheads on each deployed SLBM (individual SLBMs might carry any number up to the maximum 

load of 8), deployed Minuteman III ICBMs carry 1 warhead each (by U.S. policy, out of a maximum of 3 for that 

missile), and deployed bombers count as 1 warhead each 

(see the description in Table 2 on page 5).27

Expansion by Uploading Additional Warheads

Current versions of SLBMs and ICBMs are capable of 

carrying more warheads than they typically do under 

New START. Similarly, the next generation of delivery vehicles would also have the capacity to carry more 

warheads than they most likely would be allowed to do 

under New START rules if the treaty remained in force 

(see Table 3). 

26. For more details on those modernization programs, see 

Congressional Budget Office, Approaches for Managing the 

Costs of U.S. Nuclear Forces, 2017 to 2046 (October 2017), 

www.cbo.gov/publication/53211.

27. The counting rule for bombers was chosen to balance the 

facts that bombers are capable of carrying nuclear weapons 

but that neither the United States nor Russia keeps bombers 

loaded with those weapons on a day-to-day basis. See Senate 

Committee on Foreign Relations, Treaty With Russia on Measures 

for Further Reduction and Limitation of Strategic Offensive Arms 

(The New START Treaty), Exec. Report 111-6 (October 1, 

2010), www.congress.gov/111/crpt/erpt6/CRPT-111erpt6.pdf

(701 MB).
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 11

If enough warheads of the correct types were available, 

the current generation of forces could carry up to about 

4,600, and the next generation of forces (when fully 

fielded) could carry up to about 4,400, CBO estimates. 

(Those numbers are theoretical maximums; they include 

full weapon loads on all bombers and incorporate the 

idealized assumption that all delivery systems would be 

in good repair and available.)28 That approach would be 

roughly consistent with the counting rules of the START 

I treaty, which did not distinguish between deployed and 

nondeployed delivery vehicles and which attributed to 

28. For this analysis, CBO’s estimates of next-generation forces 

incorporate the assumption that the B-21 bomber could carry 

up to eight nuclear weapons, half the number that the B-2A 

can carry. The actual number and types of nuclear weapons 

the B-21 will carry have not been publicly disclosed. For a 

public analysis of the potential capabilities of the B-21, see 

David Cenciotti and Tom Denerly, “Let’s Have a Look at 

the New B-21 ‘Raider’ Stealth Bomber Renderings the Air 

Force Has Just Released,” The Aviationist (January 31, 2020), 

https://tinyurl.com/ya6kvudz. 

each delivery vehicle the maximum number of warheads 

used in any test of that system (except for bombers, 

which counted as fewer warheads than they were capable 

of carrying).

In all likelihood, however, the United States would not 

be able to field that many warheads in practice, primarily 

because they would not be available. According to the 

most recent unclassified data released by the Department 

of Defense, the United States’ nuclear stockpile totaled 

3,822 warheads as of 2017.29 Another estimate, from 

an oft-cited public analysis of U.S. nuclear forces, puts 

the number of strategic warheads at 3,570, comprising 800 ICBM warheads, 1,920 SLBM warheads, and 

850 bomber warheads (with an additional 230 nonstrategic warheads), as well as about 2,000 warheads that 

29. See Department of Defense, “U.S. Nuclear Weapons Claims and 

Responses” (April 2019), https://go.usa.gov/xwtvc (PDF, 2.82 

MB). 

Table 3.

U.S. Nuclear Forces, as Currently Planned

How Deployed Warheads 

Would Count Under 

Treaty Counting Rules

Triad 

Component

Delivery Systems 

Under Current Plans

Warheads If 

Delivery Systems 

Loaded to 

Maximum Capacity New START Moscow Comments

Current Generation of Forces

SSBNs 14 Ohio class submarines with

280 D5 SLBMs (20 per submarine)

2,240 1,008 1,008 8 warheads maximum per SLBM; currently 

deployed average about 4.2 per SLBM

ICBMs 450 silos with 400 MMIII missiles 1,200 400 400 3 warheads maximum per ICBM; actual 

deployed ICBMs have 1 each by policy

Bombers 43 B-52Hs and 20 B-2As 1,180 56 524 20 warheads maximum per B-52; 

16 warheads per B-2

Total 791 4,620 1,464 1,932

Next Generation of Forces

SSBNs 12 Columbia class submarines with 

192 D5 SLBMs (16 per submarine)

1,536 739 739 8 warheads maximum per SLBM; 

deployed average 4.2 per SLBM

ICBMs 450 silos with 400 GBSD missiles 1,200 400 400 3 warheads maximum per ICBM; 

1 warhead per deployed ICBM

Bombers 43 B-52Hs and 100 B-21s 1,660 128 740 20 warheads maximum per B-52; 

8 warheads per B-21

Total 783 4,396 1,267 1,879

Source: Congressional Budget Office.

GBSD = Ground-Based Strategic Deterrent; ICBM = intercontinental ballistic missile; MMIII = Minuteman III; SLBM = submarine-launched ballistic missile; 

SSBN = ballistic missile submarine; START = Strategic Arms Reduction Treaty.
12 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

have been retired and are awaiting dismantlement.30

Those estimates, if accurate, suggest that it would not be 

possible to load any of the three components of the triad 

to their full potential capacity or to field any configuration of nuclear forces with more than about 3,800 warheads, without either returning retired warheads to active 

service or producing new warheads, either of which 

could incur substantial costs and delays. CBO has not 

estimated those costs in this analysis because it is not 

clear to what extent those actions would be required.

At times, the number of available delivery systems 

would probably be smaller than CBO estimates, too. As 

current-generation delivery systems were retired and were 

replaced by newly produced next-generation systems, a 

period of reduced inventory would probably occur, particularly for SSBNs; if the program stays on schedule, the 

United States is expected to have 10 of them for several 

years (down from 14 now) before reaching the planned 

goal of 12. Maintaining current-generation systems at 

high levels of availability as they near the end of their 

operational life also might prove difficult.31

In addition to the practical reasons for fielding ICBMs 

and SLBMs at less than their full warhead loading, that 

configuration might make sense for operational and 

policy reasons. Many nuclear analysts have argued that 

placing more than one warhead on silo-based ICBMs 

(which have fixed and widely known locations) is strategically destabilizing because those missiles present an 

inviting target: By attacking such an ICBM, an adversary 

could destroy multiple warheads at once and gain an 

advantage. The 2010 Nuclear Posture Review established 

a U.S. policy to field only single-warhead ICBMs, and 

the 2018 NPR continued that policy. Operationally, 

increasing the weight that a missile has to carry reduces 

30. That estimate combines weapons in the active and inactive 

stockpiles. Weapons in the inactive stockpile have had certain 

limited-lifetime components removed to reduce maintenance 

requirements. If needed, those weapons could be returned to 

active status; the time required to do so would depend on the 

condition of each weapon, whether it was up to date on life 

extensions and other modifications that active weapons of its type 

received, and the availability of limited-lifetime components, 

particularly tritium. For an unclassified analysis of the size and 

composition of the U.S. stockpile, see Hans M. Kristensen and 

Matt Korda, “United States Nuclear Forces, 2020,” Bulletin of the 

Atomic Scientists (January 2020), https://thebulletin.org/2020/01/

united-states-nuclear-forces-2020/. 

31. See Rachel S. Cohen, “Report: ICBMs to Fall Short of Mission 

Needs in 2026,” Air Force Magazine (March 30, 2020), 

https://tinyurl.com/ycrfymmt. 

its maximum range, so carrying the full load of warheads 

on an ICBM might require changing its assigned targets. 

Similarly, loading SLBMs with more warheads could 

force SSBNs to operate in areas closer to their targets 

(as they did during the Cold War). That configuration 

would require more time for the submarines to transit to 

and from their operating areas at the beginning and end 

of their deployments and would reduce planners’ flexibility in choosing operating areas. 

Expansion by Fielding Additional Delivery Vehicles

The United States could expand its nuclear forces 

by fielding additional strategic delivery vehicles—an 

approach that would provide limited options for growth 

with the current generation of delivery vehicles but 

more options for the next generation of vehicles. Those 

additional purchases of next-generation systems would 

probably not be available for decades, however, unless 

production capacity for DoD’s delivery systems and 

DOE’s nuclear production facilities was expanded, which 

would require a significant investment.

Current-Generation Delivery Vehicles. Potentially, the 

number of deployed current-generation delivery vehicles could be increased from the current 700 to as many 

as about 880 (the number that the United States had 

before New START) without producing new systems, 

probably within several years of the decision to do so. 

Expanding the number of current-generation delivery 

vehicles beyond 880, however, is unlikely to occur. All of 

those systems have been in service for many years, and 

replacement systems are in development. For those reasons, CBO did not consider the possibility of producing 

additional current-generation systems. 

To meet the limits for deployed delivery vehicles under 

the New START treaty, the United States had to reduce 

its inventory of each type of vehicle. To do so, it took 

three actions: disabling four SLBM launch tubes on each 

Ohio class SSBN (decreasing the number of operational tubes from 24 to 20 per submarine), removing 

50 Minuteman III ICBMs from their silos, and converting about 30 B-52H bombers to conventional-only 

missions. 

Increasing the number of deployed delivery vehicles 

would mean reversing at least one of those actions. The 

most straightforward would be increasing the number 

of deployed ICBMs by returning up to 50 missiles to 

their silos, because the United States elected to keep 

the 50 emptied silos in an operational status to serve 
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 13

as backups during the GBSD program’s planned silo 

refurbishment. The total stock of Minuteman III missiles 

is limited, though, so placing additional missiles in silos 

might adversely affect their testing and reliability program.32 Before the missiles were removed, the Air Force 

estimated that the costs of removing them from their 

silos and storing them would be $20 million (in current dollars) over the 2014–2018 period. Returning the 

missiles to their silos might incur similar costs, although 

some of those silos would probably be left empty to 

facilitate refurbishment. 

Some analysts have argued that it may be possible to 

reverse the changes made to SSBN tubes or B-52H 

bombers as a means to expand the number of currentgeneration delivery systems. Those actions—if possible—

could probably be accomplished more quickly and at a 

lower cost than purchasing new next-generation delivery 

vehicles.

Next-Generation Delivery Vehicles. Expanding the 

number of next-generation delivery systems could be 

accomplished by increasing the number produced. 

Production of each of those systems is expected to run 

for many years. If the additional units were produced at 

the end of the planned production run for each system, 

the full complement of additional systems would probably not be available before the mid-2040s. 

If DoD funded additional production facilities, then it 

might be possible to get those extra systems deployed 

sooner by accelerating their production. Construction 

costs could be substantial, though, particularly for 

SSBNs. And even if production started sooner than 

planned, it would still take many years to produce the 

desired quantity of delivery vehicles.

Costs of Producing New Nuclear Systems 

The main contributors to the costs of producing new 

nuclear systems are the costs to purchase additional 

delivery vehicles and the costs to produce new warheads. 

CBO used analyses from its previous reports to estimate 

the marginal costs of producing additional delivery 

systems and warheads. But CBO’s estimates of the costs 

to expand nuclear forces to treaty levels do not include 

DOE’s costs to produce additional warheads, because 

information about the current inventory of weapons is 

classified so it is not clear how many warheads would be 

required. 

32. Ibid. 

The estimates also do not include other potential sources 

of substantial costs: the cost to sustain new warheads for 

the delivery systems to carry, should that be necessary; 

the cost to add production capacity for delivery systems 

or for warheads, should that be necessary; and the cost to 

establish and operate new bases for the delivery systems, 

should those be required.

Costs of Purchasing Additional Delivery Vehicles

To estimate the costs of producing additional delivery 

systems—submarines, missiles, and bombers—CBO 

grouped those systems into sets (see Table 4). For example, the estimated cost for an SSBN includes the cost of 

the submarine plus the cost of 18 SLBMs, comprising 

the 16 that a single SSBN carries plus 2 spares. Using 

that general approach, CBO estimates that purchasing one outfitted Columbia class SSBN would cost 

$8.5 billion, one launch control center’s worth of silos 

and ICBMs would cost $1.0 billion, and one B-21 with 

LRSO cruise missiles would cost about $0.5 billion (all 

in 2020 dollars).

Unlike ICBMs and SSBNs, which are exclusively nuclear 

systems, bombers perform both nuclear and nonnuclear missions. CBO’s estimates include the full cost 

of additional B-21 bombers because they are needed to 

reach the desired levels of nuclear forces. Those aircraft 

also would be available to perform nonnuclear missions, 

however, and thus would increase U.S. conventional 

capabilities as well.

Those estimates draw heavily on previously published 

CBO analyses. In particular, CBO’s approach for estimating the production costs for delivery systems in this 

report is the same one it used in its 2017 report on the 

30-year costs of nuclear forces.33 Production costs were 

estimated using a model in which additional production 

would occur at the end of the planned production run, 

when the unit cost of produced units is typically at its 

lowest. Those production runs are currently scheduled to 

be completed in the late 2030s or early 2040s. If additional delivery systems were desired earlier, it might be 

necessary to construct additional production facilities, 

but CBO did not estimate the costs to do so. 

33. Costs in this report have been updated to 2020 dollars. For 

details on the methodology CBO used, see Congressional Budget 

Office, Approaches for Managing the Costs of U.S. Nuclear Forces, 

2017 to 2046 (October 2017), Appendix A, www.cbo.gov/

publication/53211.
14 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

CBO’s estimates of marginal operation and sustainment 

costs are based on the actual costs of analogous systems.34

They incorporate the assumption that, as the size of the 

fleet changes, half of all operation and sustainment costs 

would be fixed, and half would vary linearly with the size 

of the force. If the size of the fleet doubled, for instance, 

the fixed half of operation and sustainment costs would 

stay the same, whereas the variable half of those costs 

would double, resulting in operation and sustainment 

costs for the double-sized fleet that were 150 percent of 

the costs of the original fleet.

Costs of Producing New Warheads 

Expanding the number of warheads in the stockpile 

could add to costs in two ways: The additional warheads 

would need to be produced, and larger production facilities might need to be built to support a larger stockpile. 

Although CBO could not estimate the total costs for the 

Department of Energy to produce enough new warheads 

to reach the limits under the various treaties, it was able 

to roughly estimate the average cost of producing each 

additional warhead by gauging the average marginal cost 

to produce a new warhead of a type that is already in 

the stockpile. (That estimate does not include the costs 

to develop the design and procedures for producing 

34. Sustainment means providing incremental upgrades to a system 

over time, often by adding components that are easier to 

maintain or that add capability.

the warhead.) DOE is in the process of performing life 

extensions on essentially all of the types of warheads in 

the stockpile. Drawing on analysis done for a previous 

report, CBO estimates that the average production cost 

per warhead for those LEPs would be about $9 million 

to $12 million, assuming that there was a one-to-one 

replacement of warheads in the existing active stockpile. 

One variable that would affect the costs of producing 

new warheads is whether enough plutonium pits of the 

appropriate type would be available.35 Life-extension 

programs generally reuse a plutonium pit from an 

existing warhead, but there may not be enough existing pits to support a substantial increase in the size of 

the stockpile. DOE is in the planning stages for a new 

plutonium pit facility, but completion would be years 

away. Based on an analysis of DOE’s information about 

operating costs for that facility when it reaches full 

production capacity of 50 pits per year, CBO estimates 

that the marginal cost of producing a pit would be about 

$6 million. Combining that cost with the other warhead 

production costs yields a rough marginal cost estimate 

of $15 million to $20 million per warhead. Thus, if 

3,000 new warheads were required to expand U.S. forces 

to the START I limit of 6,000, for example, the total 

35. A pit is a hollow shell of fissile material, such as plutonium, at 

the core of a modern nuclear weapon. Detonation of the weapon 

begins with the implosion of the pit. Each type of nuclear 

weapon generally uses a custom-designed pit.

Table 4.

CBO’s Estimates of DoD’s Marginal Costs of Purchasing Additional Next-Generation Delivery Vehicles

Triad Component Items Purchased

Maximum 

Warhead 

Capacity 

Added

Marginal One-Time 

Acquisition Cost 

(Billions of 

2020 dollars)

Additional Annual 

Operation and 

Sustainment Costs 

(Millions of 

2020 dollars)

Department of 

Energy's Additional 

Costs to Produce, 

Sustain, and Store 

New Warheads Comments

SSBNs 1 Columbia class SSBN 

and 18 D5 SLBMs

128 8.5 180 Not estimated Includes 2 spare SLBMs

ICBMs 10 silos and 

11 GBSD ICBMs

30 1.0 20 Not estimated ICBMs are grouped as 10 

per launch control center; 

includes 1 spare ICBM

Bombers 1 B-21 and 10 LRSO 

cruise missiles

8 0.5 40 Not estimated Includes 2 spare LRSOs

Source: Congressional Budget Office, using information from the Department of Defense.

Marginal cost is the cost added by producing one additional unit of a product or service.

CBO did not estimate DoD’s costs of new bases or new facilities for training and maintenance (if needed).

GBSD = Ground-Based Strategic Deterrent; ICBM = intercontinental ballistic missile; LRSO = Long-Range Standoff weapon; SLBM = submarine-launched 

ballistic missile; SSBN = strategic ballistic missile submarine.
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 15

cost for new warheads would be about $45 billion to 

$60 billion. That estimate is highly uncertain, though, 

primarily because it is not clear how well LEP costs serve 

as an analogue for the costs of producing a new warhead. 

If the number of warheads in the stockpile was 

expanded, DOE might need to make some changes to its 

weapons complex beyond those it already has planned. 

Many of its production facilities are more than 40 years 

old. Over the past several years, DOE has developed 

a plan to rebuild much of the infrastructure used to 

produce the components that make up nuclear warheads: the plutonium pits; strategic materials, such as 

tritium; and other nonnuclear components, including 

radiation-hardened electronics and the conventional 

explosives used to begin the nuclear chain reaction in the 

warhead. 

In its fiscal year 2021 budget submission, DOE estimated that it would need $15.5 billion (in current 

dollars) to modernize its production facilities over the 

2021–2025 period, and additional funding for that 

effort is slated to run through the mid-2040s. If DOE’s 

planned facilities are sized to support a future stockpile 

that is the same size as the current one, though, and later 

the decision is made to expand the stockpile substantially, those planned facilities might need to be expanded 

as well. DOE also would have to increase its capacity to 

maintain a larger stockpile. Those changes, if necessary, 

would incur additional costs, possibly substantial, particularly if the United States returned its nuclear forces to 

START I levels.

Costs of Expanding Strategic Nuclear Forces 

to the Limits Under Previous Treaties

Because it is unclear how the United States might expand 

its strategic nuclear forces if New START expired, CBO 

looked at a range of possible outcomes using the limits 

under the Moscow Treaty, the START II treaty, and the 

START I treaty. Each treaty had a unique set of rules for 

counting the number of warheads and delivery vehicles. 

To make the possible outcomes under the various treaties 

easier to compare, CBO used a single set of counting 

rules—those from the Moscow Treaty, which come the 

closest to counting the actual number of deployed warheads (see Box 1).

CBO’s Approach

The United States could expand its nuclear forces by 

uploading warheads on missiles, fielding additional 

delivery systems, or doing both. Because myriad combinations are possible, CBO estimated costs for the full 

range of possible combinations but focused on two general approaches—one at each end of the spectrum—to 

show the range of potential costs:

• A lower-cost and less flexible approach under which 

the United States would expand its nuclear forces 

primarily by uploading warheads on missiles and 

increasing the number of warheads allocated to each 

bomber to, or nearly to, the maximum level while 

fielding as few additional delivery systems as possible; 

and

• A more flexible and higher-cost approach under 

which the United States would expand its nuclear 

forces primarily by fielding additional delivery 

systems while maintaining, to the extent possible, 

the current levels of warhead loading on missiles and 

warheads allocated to bombers.

The lower-cost approach would be less expensive generally because it would lead to the purchase of fewer new 

delivery systems. The more flexible approach would be 

more expensive generally, but it would allow expanded 

forces to operate in a manner similar to that of current 

forces by maintaining current warhead loadings. 

Increasing the number of warheads on missiles reduces 

their maximum range. Under the lower-cost approach, 

fully loaded ICBMs might not be able to reach all of 

their currently assigned targets, and SSBNs might have 

to change their operating areas to reach all of their 

current targets. Having fewer warheads on delivery 

vehicles—as the more flexible approach would do—

might provide more capability to execute limited nuclear 

strikes, yielding more flexibility in managing nuclear 

escalation. 

Criteria That CBO Considered. In constructing 

potential force structures, CBO considered only those 

in which warheads would be distributed among the 

components of the triad in proportions that were 

roughly similar to those of current forces and planned 

next-generation forces (when possible). Historically, 

each component of the triad has been thought to make 

a unique contribution to deterrence, so fielding an 

expanded force with a structure close to that of current 
16 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

or planned forces would maintain a similar mix of those 

deterrence features.36

Applying the Moscow Treaty’s counting rules to 

current-generation forces means that about half of 

accountable warheads are carried on SLBMs, and ICBMs 

and bombers each account for about one-quarter of warheads. Similarly, for next-generation forces as currently 

36. In brief, SSBNs provide survivable nuclear weapons and thus 

guarantee the ability to execute a retaliatory second strike if 

an adversary strikes the United States; ICBMs provide rapid 

response and a large number of targets that raise the threshold 

for a potential adversary’s disarming first strike; and bombers 

provide flexibility by allowing leaders to ramp up operations 

quickly (to signal intent to an adversary) and by being able to be 

recalled after launch if circumstances change. For more details, 

see Congressional Budget Office, Approaches for Managing the 

Costs of Nuclear Forces, 2017 to 2046 (October 2017), Chapter 3, 

www.cbo.gov/publication/53211. 

planned, SLBMs and bombers would each account for 

about 40 percent of warheads under those counting 

rules, and ICBMs would account for about 20 percent. 

CBO considered force structures that fit roughly within 

the range between those two cases. 

In addition, CBO considered only expanded forces 

that would use the same delivery systems as currently 

planned—that is, Columbia class SSBNs, GBSD silobased ICBMs, B-52H bombers, and B-21 bombers. The 

United States could consider developing other delivery 

systems, though, particularly if forces were expanded 

substantially. For example, DoD’s original analysis of 

alternatives that led to creation of the GBSD program 

also considered a mobile ICBM concept.37 Development 

37. See Jason Sherman, “Trump Administration Wants to Retain 

Option for Road-Mobile GBSD Variant,” Inside Defense (July 18, 

2019), https://tinyurl.com/y85fq6zz. 

Box 1.

Counting Rules Used in This Analysis

To estimate the potential costs of expanding strategic nuclear 

forces to the levels defined in the Moscow, START II, and 

START I arms control treaties, the Congressional Budget Office 

needed to select an appropriate method for counting the 

number of warheads for a given set of nuclear forces. Each 

treaty has a set of negotiated counting rules to calculate the 

number of “accountable” warheads of each party to determine 

if they comply with the treaty’s limits.1 Generally, those rules 

were customized to address concerns about the makeup of the 

forces at the time; for example, when the START I treaty was 

negotiated in 1991, the United States was concerned about 

Russia fielding large intercontinental ballistic missiles (ICBMs) 

capable of carrying many warheads, so the rules count each 

missile as having the maximum number of warheads that a 

missile can carry rather than the (smaller) number with which 

it might typically be outfitted. Because of those idiosyncrasies, 

the numbers of accountable warheads can differ markedly 

depending on which counting rules are applied to a given force 

(see Table 2 on page 5). 

For consistency in comparing illustrative forces, CBO selected 

a single set of counting rules—those used for the Moscow 

Treaty in 2002—to determine the number of accountable warheads for each of the forces. Specifically, CBO used the rules 

1. Accountable warheads are those that count toward the maximum overall 

limits provided for in the treaty. They are not necessarily the same as the 

actual number of deployed warheads.

described in the transmittal documents submitting the treaty 

to the Congress: the actual number of warheads on deployed 

ICBMs and submarine-launched ballistic missiles (SLBMs), plus 

the number of warheads either loaded on deployed bombers 

or stored at active bomber bases.2

That formulation corresponds roughly to the number of warheads that the United States could bring to bear within a few 

weeks during a crisis and thus has a meaningful operational 

basis, particularly in a world without limits on nuclear forces. 

On the basis of its analysis of U.S. annual reports on treaty 

implementation and unclassified analyses of the makeup 

of U.S. strategic forces, CBO estimates that the number of 

accountable bomber warheads when the Moscow Treaty was 

in force was approximately half of the maximum warhead 

capacity for the deployed bomber force. In CBO’s application 

of the Moscow Treaty’s counting rules, deployed ICBMs include 

silos that have ICBMs in them, and deployed SLBMs include all 

missiles carried by submarines that are not being overhauled. 

CBO’s application of those rules also incorporates the assumption that 90 percent of delivery systems are deployed.

2. See “Message From The President of the United States Transmitting 

the Treaty Between the United States of America and the 

Russian Federation on Strategic Offensive Reduction, Signed 

at Moscow on May 24, 2002,” Senate Treaty Document 107-8, 

www.congress.gov/107/cdoc/tdoc8/CDOC-107tdoc8.pdf (522 KB).
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 17

of a new delivery system would incur additional costs, 

but it could lead to lower overall costs than those of the 

other force structures considered in this report, and the 

United States could choose to pursue it for operational 

or financial reasons. However, CBO did not consider the 

development of any new delivery systems in estimating 

the costs of expanded forces.

CBO’s Estimates of Costs. To show the range of DoD’s 

potential costs under each treaty, CBO estimated the 

costs of the full range of possible combinations of forces 

that added up to the treaty’s limit on warheads and still 

met the criteria described above. Those combinations 

were based on varying the number of components: 

SSBNs and the warheads carried by each SLBM on those 

submarines, ICBMs and the warheads carried by each 

of those missiles, and B-21 bombers. (The number of 

B-52 bombers was not varied.) 

Unlike ICBMs and SSBNs, which are exclusively nuclear 

systems, bombers perform both nuclear and nonnuclear 

missions. CBO’s estimates include the full cost of additional B-21 bombers because they would be needed to 

reach the desired levels of nuclear forces. Those aircraft 

also would be available to perform nonnuclear missions, 

however, and thus would increase U.S. conventional 

capabilities as well.

For treaties that have a range for the maximum number 

of warheads they allow, CBO assessed the cost of forces 

at the lower end of that limit—1,700 for the Moscow 

Treaty and 3,000 for the START II treaty. CBO did 

not consider decreasing any components of the triad; in 

other words, it excluded configurations that would field 

fewer than the planned number of delivery systems of 

any type or that would load missile warheads at an average of less than 4 per SLBM or 1 per ICBM. 

The resulting set of possible configurations provided a 

range of potential costs. Force configurations that correspond to what CBO has referred to as the lower-cost 

approach (which favors uploading warheads over purchasing any new delivery systems) generally have costs 

at the low end of the distribution for a given treaty; 

configurations that correspond to the more flexible 

approach (which prioritizes purchasing enough delivery 

systems to require little or no uploading of warheads on 

missiles beyond current levels) generally have costs at the 

high end of the distribution. Those two approaches are 

meant to illustrate what force structures and costs would 

look like at the ends of the cost distribution. Many other 

approaches and configurations are possible. 

Regardless of the approach chosen, actual costs for the 

forces in each range would probably exceed CBO’s estimates because they exclude two types of costs. 

• First, they exclude any costs incurred by DOE for 

additional warheads. If production of new warheads 

was necessary to reach the levels for a certain treaty, 

the process could take longer, and DOE could incur 

substantial costs. 

• Second, they exclude any costs for DoD to build 

additional weapons storage and maintenance facilities 

at bases or to establish operations at any additional 

bases, if those became necessary. 

CBO has not estimated those costs because it is not clear 

whether and to what extent new warheads or new facilities might be needed. The size of those excluded costs 

probably increases with the extent of the expansion of 

DoD’s forces, so greater expansion means more costs that 

are not included in CBO’s estimates.

Costs of Expanding Forces to Moscow Treaty Limits

Under the Moscow Treaty’s counting rules, both the 

current generation of forces and the planned next 

generation of forces would meet its limit of 1,700 to 

2,200 warheads with no changes and, thus, would not 

incur any additional costs (see Table 3 on page 11). 

Although that limit is higher than currently allowed 

under New START, more warheads are counted toward 

that limit under the Moscow Treaty’s counting rules, 

which fully account for the weapons that have been 

assigned to bombers. Under New START’s counting 

rules, by contrast, each bomber accounts for only one 

warhead.

Costs of Expanding Forces to START II Treaty Limits

CBO examined two approaches to constructing forces 

that would carry 3,000 to 3,500 warheads, the number 

allowed under the START II treaty.38 The lower-cost 

approach would upload warheads on existing and 

next-generation forces, and the more flexible approach 

would purchase enough additional next-generation 

delivery vehicles to reach START II limits using warhead 

38. START II’s limits on warheads were to be implemented in two 

phases. This analysis uses the more restrictive limits from the 

second phase.
18 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

loadings as they are today (to preserve the flexibility 

provided by that configuration).

Lower-Cost Approach. The United States could reach 

the START II warhead limit for the current and next 

generation of forces by increasing warhead loadings to 

near their maximum capacity on ICBMs and SLBMs 

and increasing the number of warheads allocated to 

bombers to near their maximum capacity (see Table 5, 

top panel). If enough warheads of the appropriate types 

were available, increasing warhead loadings to that extent 

could probably be accomplished within a few years, 

CBO estimates, and would cost about $100 million 

(based on the cost that DoD has reported for removing 

warheads from delivery systems to comply with the limit 

under the New START treaty). 

Increasing the number of warheads to 3,000 or more 

would put the total number close to the current stockpile 

of 3,800 active and inactive warheads. Probably only 

a few force structures, if any, could be fielded solely by 

uploading warheads without producing any new warheads. And producing new warheads would extend the 

time required to reach the START II warhead levels and 

would boost costs (which CBO did not estimate).

Table 5.

Examples of Nuclear Force Structures That Could Be Implemented to Reach START II Warhead Limits

DoD's Additional Costs

(Billions of 2020 dollars)

Triad 

Component Delivery Systems

Warheads 

at Maximum 

Capacity

Deployed 

Warheads 

(CBO's 

estimate)

One-Time 

Acquisition 

Costs

Annual 

Operation and 

Sustainment 

Costs

Department of Energy’s 

Additional Costs to 

Produce, Sustain, and 

Store New Warheads Comments

Lower-Cost and Less Flexible Approach 

SSBNs 12 Columbia class 

submarines with 

192 D5 SLBMs

1,536 1,408 0 0 Not estimated No additional SSBNs; 8 warheads per SLBM, on average

ICBMs 450 silos with 

405 GBSD missiles

1,350 810 0 0 Not estimated No additional ICBMs; 2 warheads per ICBM, on average

Bombers 43 B-52Hs and 

100 B-21s

1,660 782 0 0 Not estimated No additional bombers; 

warheads at about half-full 

bomber capacity

Total 785 4,546 3,000 0a 0

More Flexible and Higher-Cost Approach

SSBNs 19 Columbia class 

submarines with 

304 D5 SLBMs

2,432 1,169 60 1 Not estimated 7 additional SSBNs with 

SLBMs; 4.3 warheads per 

SLBM, on average

ICBMs 550 silos with 

495 GBSD missiles

1,650 495 10 0 Not estimated 100 additional ICBMs; 

1 warhead per ICBM

Bombers 43 B-52Hs and 

266 B-21s

2,988 1,336 91 7 Not estimated 166 additional B-21s with 

LRSOs; warheads at about 

half-full bomber capacity

Total 1,163 7,070 3,000 160b 8b

Source: Congressional Budget Office.

The approaches described in this table are two illustrative examples of the many force structures that CBO included in its cost range for expanding U.S. 

forces to START II treaty levels. The costs are estimated using the marginal cost factors from Table 4. The lower-cost approach to increasing warheads 

to START II limits (3,000 to 3,500) would increase the number of warheads on each missile; the more flexible approach would increase the number of 

delivery vehicles.

DoD = Department of Defense; GBSD = Ground-Based Strategic Deterrent; ICBM = intercontinental ballistic missile; LRSO = Long-Range Standoff 

weapon; SLBM = submarine-launched ballistic missile; SSBN = strategic ballistic missile submarine; START = Strategic Arms Reduction Treaty.

a. Under the lower-cost approach, warheads could be uploaded only at a onetime additional cost of about $100 million. That approach might require 

the production of new warheads, but CBO did not estimate the costs to do so. 

b. The more flexible approach could incur costs for new warhead production, sustainment and infrastructure, production facilities for new delivery 

systems, and new bases and training facilities; CBO did not estimate the costs for any of those items, however.
August 2020 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires 19

More Flexible Approach. The United States could expand 

to START II warhead levels for next-generation forces 

by purchasing additional delivery systems. Warhead 

loading levels would stay close to their current values 

(4.2 per SLBM, on average, and 1 per ICBM), and 

warheads allocated to the bomber fleet would remain at 

about half of the maximum capacity. That more flexible 

approach would incur additional onetime acquisition 

costs of between $114 billion and $172 billion over 

several decades and additional operation and sustainment costs of between $3 billion and $8 billion a year, 

CBO estimates. Those costs would depend on the mix 

of additional delivery systems purchased to preserve the 

current relative distribution of warheads among the triad’s 

components. 

As an example, one potential configuration of forces 

would require DoD to purchase 7 additional Columbia 

class SSBNs and associated missiles, 100 additional 

GBSD ICBMs and associated infrastructure, and 

166 additional B-21 bombers with cruise missiles (see 

Table 5 on page 18, bottom panel).39 To field and 

maintain such a force, DoD would incur onetime 

acquisition costs of $160 billion and operating and sustainment costs of $8 billion a year, CBO estimates. Any 

additional costs for DOE would elevate those totals.

The more flexible approach would probably require the 

production of new warheads, which would increase costs. 

CBO did not estimate those additional costs.

Costs of Expanding Forces to START I Treaty Limits

CBO used the same two approaches to illustrate the 

range of possible forces under START I, which limits the 

number of warheads to a total of 6,000 and the number 

of delivery systems to 1,600.40 The lower-cost approach 

would emphasize uploading forces and would require 

the purchase of as few additional systems as possible. The 

more flexible approach would emphasize warhead loadings that were roughly similar to those of current forces.

39. The addition of 100 ICBMs comprises adding 100 silos and 110 

missiles. CBO’s estimate of the number of deployed warheads 

incorporates the assumption that missiles would be deployed 

in 90 percent of those silos (that is, they are loaded into a silo) 

at any given time, which is consistent with the current fraction 

of ICBMs deployed by DoD. The remaining missiles would be 

added to the Air Force’s inventory and would be available for 

deployment if that was desired.

40. CBO did not apply the sublimits that the treaty created for how 

the warheads would be distributed among the components of the 

triad, because the treaty is no longer in effect.

Because the 6,000-warhead limit would exceed the 

maximum capacity of both current- and next-generation 

forces, reaching it would require the purchase of additional delivery systems—a prospect that would be feasible only for next-generation forces. 

Lower-Cost Approach. To minimize the number of 

additional delivery systems needed under the lower-cost 

approach, ICBMs and SLBMs could be uploaded to the 

greatest extent possible, and the bomber fleet could be 

sized to match maximum capacity to warheads allocated 

to the fleet. If missiles were at their full loading (8 warheads per SLBM and 3 warheads per ICBM), reaching 

6,000 deployed warheads would cost DoD $88 billion to 

$149 billion in additional onetime acquisition costs and 

$4 billion to $10 billion a year in additional operation 

and sustainment costs. The costs would depend on the 

makeup of the additional delivery systems purchased, 

although any configuration would need to maintain 

roughly the same relative distribution of warheads 

among the components of the triad.

One potential configuration of forces would comprise 

3 additional Columbia class SSBNs with missiles, 

150 additional GBSD ICBMs, and 153 additional 

B-21 bombers with cruise missiles. That setup would 

cost DoD an additional $124 billion in acquisition costs 

and $7 billion annually in additional operation and 

sustainment costs (see Table 6, top panel).41

The lower-cost approach would probably require the 

production of new warheads, which could substantially 

increase costs. CBO did not estimate those additional 

costs.

More Flexible Approach. It is not possible to reach 

6,000 warheads while fully preserving the levels of warhead loading in the current force and remaining below 

the START I limit of 1,600 delivery systems. To remain 

below the limit on delivery vehicles, CBO considered 

force configurations that would load a single warhead 

on all ICBMs (maintaining current U.S. policy) and 

load SLBMs to near their maximum value. Those force 

configurations would not maintain the current relative 

41. The addition of 150 ICBMs comprises adding 150 silos and 165 

missiles. CBO’s estimate of the number of deployed warheads 

incorporates the assumption that missiles would be deployed 

in 90 percent of those silos (that is, they are loaded into a silo) 

at any given time, which is consistent with the current fraction 

of ICBMs deployed by DoD. The remaining missiles would be 

added to the Air Force’s inventory and would be available for 

deployment if that was desired.
20 The Potential Costs of Expanding U.S. Strategic Nuclear Forces If the New START Treaty Expires August 2020

distribution of warheads among the components of the 

triad—the ICBM component would carry a smaller 

fraction of warheads than it does currently. Under 

those conditions, DoD would incur $410 billion to 

$439 billion in additional onetime acquisition costs and 

$24 billion to $28 billion in additional annual operation 

and sustainment costs, CBO estimates. The range of 

costs reflects the makeup of additional delivery systems 

purchased. 

One potential configuration would add 12 Columbia 

class SSBNs with missiles and 586 B-21 bombers with 

cruise missiles to the force but would not change the 

number of GBSD ICBMs. Such a force would cost DoD 

$423 billion in additional onetime acquisition costs and 

$26 billion in additional operation and sustainment 

costs each year, in CBO’s estimation (see Table 6, bottom 

panel).

The more flexible approach would probably require the 

production of new warheads, which could substantially 

increase costs. CBO did not estimate those additional costs.

Table 6.

Examples of Nuclear Force Structures That Could Be Implemented to Reach START I Warhead Limits

DoD's Additional Costs

(Billions of 2020 dollars)

Triad 

Component Delivery Systems

Warheads 

at Maximum 

Capacity

Deployed 

Warheads 

(CBO's 

estimate)

One-Time 

Acquisition 

Costs

Annual 

Operation and 

Sustainment 

Costs

Department of Energy’s 

Additional Costs to 

Produce, Sustain, and 

Store New Warheads Comments

Lower-Cost and Less Flexible Approach 

SSBNs 15 Columbia class 

submarines with 

240 D5 SLBMs

1,920 1,792 26 1 Not estimated 3 additional SSBNs with 

SLBMs; 8 warheads per 

SLBM, on average

ICBMs 600 silos with 

540 GBSD missiles

1,800 1,620 14 0 Not estimated 150 additional ICBMs; 3 warheads per ICBM, on average

Bombers 43 B-52Hs and 

253 B-21s

2,884 2,576 84 6 Not estimated 153 additional B-21s with 

LRSOs; warheads at full 

bomber capacity

Total 1,059 6,604 5,988 124 7

More Flexible and Higher-Cost Approach

SSBNs 24 Columbia class 

submarines with 

384 D5 SLBMs

3,072 2,746 102 2 Not estimated 12 additional SSBNs with 

SLBMs; 7.8 warheads per 

SLBM, on average

ICBMs 450 silos with 

405 GBSD missiles

1,350 405 0 0 Not estimated No additional ICBMs; 

1 warhead per ICBM

Bombers 43 B-52Hs and 

686 B-21s

6,348 2,850 321 24 Not estimated 586 additional B-21s with 

LRSOs; warheads at half-full 

bomber capacity

Total 1,563 10,770 6,001 423 26

Source: Congressional Budget Office.

The approaches described in this table are two illustrative examples of the many force structures that CBO included in its cost range for expanding U.S. 

forces to START I treaty levels. The costs are estimated using the marginal cost factors from Table 4. The lower-cost approach to increasing warheads 

to START I’s limit of 6,000 would increase the number of warheads on each missile and purchase the minimum number of delivery vehicles necessary 

to reach the limit; the more flexible approach would maintain as much as possible the current number of warheads loaded on missiles and allocated to 

bombers by purchasing enough delivery systems.

Both the lower-cost and more flexible approaches could incur costs for new warhead production, sustainment and infrastructure, production facilities 

for new delivery systems, and new bases and training facilities; CBO did not estimate the costs for any of those items, however.

DoD = Department of Defense; GBSD = Ground-Based Strategic Deterrent; ICBM = intercontinental ballistic missile; LRSO = Long-Range Standoff 

weapon; SLBM = submarine-launched ballistic missile; SSBN = strategic ballistic missile submarine; START = Strategic Arms Reduction Treaty.
Tables

1. Approaches for Fielding Nuclear Warheads at Selected Treaty Limits 2

2. Details of Recent Strategic Arms Control Treaties 5

3. U.S. Nuclear Forces, as Currently Planned 11

4. CBO’s Estimates of DoD’s Marginal Costs of Purchasing Additional 

Next-Generation Delivery Vehicles 14

5. Examples of Nuclear Force Structures That Could Be Implemented to 

Reach START II Warhead Limits 18

6. Examples of Nuclear Force Structures That Could Be Implemented to 

Reach START I Warhead Limits 20

Figure

1. Estimated Total DoD Production Costs for Planned Next-Generation 

Nuclear Forces and Expanded Nuclear Forces at Different Force Levels 3

List of Tables and Figures
About This Document

This Congressional Budget Office report was prepared at the request of the Chairman of the 

House Armed Services Committee and the Ranking Member of the Senate Foreign Relations 

Committee. In keeping with CBO’s mandate to provide objective, impartial analysis, the report 

makes no recommendations.

Michael Bennett prepared the report with assistance from Joshua Wolfram, a visiting fellow 

at CBO from the Air Force, and with guidance from David Mosher and Edward G. Keating. 

Raymond J. Hall assisted in the research. John Kerman fact-checked the report.

Alissa Ardito Ashcroft of CBO provided helpful comments, as did Franklin C. Miller of the 

Scowcroft Group, Kingston Reif of the Arms Control Association, and Frank Rose of the 

Brookings Institution. (The assistance of external reviewers implies no responsibility for the final 

product, which rests solely with CBO.)

Mark Doms and Robert Sunshine reviewed the report. Christine Bogusz was the editor, and 

Robert Rebach was the graphics editor and cover illustrator. An electronic version is available on 

CBO’s website (www.cbo.gov/publication/56475).

CBO continually seeks feedback to make its work as useful as possible. Please send any comments 

to communications@cbo.gov.

Phillip L. Swagel

Director

August 2020