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Updated July 19, 2024
Defense Primer: Strategic Nuclear Forces
The United States is in the process of modernizing its
Rationale for the Triad
strategic nuclear forces. This modernization effort includes
Early in the Cold War, the United States developed three
numerous Department of Defense (DOD) major defense
types of nuclear delivery vehicles, in large part because
acquisition programs, some of which are annually assessed
each of the military services wanted part of the U.S. nuclear
by the Government Accountability Office, and warhead
arsenal. Eventually, DOD came to argue that different
modernization programs implemented by the National
basing modes’ complementary strengths could enhance
Nuclear Security Administration (NNSA), a semi-
nuclear deterrence. As the 2010 Nuclear Posture Review
autonomous agency in the Department of Energy. In 2023,
(NPR), a periodic assessment of U.S. nuclear policy,
the Congressional Budget Office estimated that U.S.
summarized the post-Cold War evolution of this thinking:
programs to operate and modernize nuclear forces would
cost $756 billion over the next 10 years. The FY2025 DOD
[SSBNs] and the SLBMs they carry represent the
budget requests “$49.2 billion for the modernization,
most survivable leg of the U.S. nuclear Triad.…
sustainment, and operations of all three legs of the nuclear
Single-warhead ICBMs contribute to stability, and
triad.” Members of Congress have shown strong interest in
like SLBMs are not vulnerable to air defenses.
conducting oversight of U.S. nuclear modernization efforts.
Unlike ICBMs and SLBMs, bombers can be visibly
The Nuclear Triad
deployed forward, as a signal in crisis to strengthen
deterrence of potential adversaries and assurance of
Since the early 1960s, the United States has maintained a
allies and partners.
“triad” of strategic nuclear delivery vehicles. These include
long-range land-based intercontinental ballistic missiles
The U.S. government has reaffirmed the value of the
(ICBMs), long-range submarine-launched ballistic missiles
nuclear triad and the importance of its modernization in a
(SLBMs) on strategic nuclear submarines (SSBNs), and
series of NPRs. The Obama Administration stated in the
long-range heavy bombers. The U.S. nuclear warhead
2010 NPR that the unique characteristics of each leg of the
stockpile has decreased in number as the United States
triad were important to “maintain strategic stability at
changed nuclear planning requirements after the Cold War
reasonable cost, while hedging against potential technical
and complied with arms control agreements.
problems or vulnerabilities.” The Trump Administration
stated in the 2018 NPR that “the triad’s synergy and
U.S. strategic forces are currently limited by the 2011 U.S.-
overlapping attributes help ensure the enduring
Russian New START treaty. Table 1 displays U.S. nuclear
survivability of our deterrence capabilities against attack
forces, as of September 1, 2022, accountable under that
and our capacity to hold a range of adversary targets at risk
treaty. The United States had 1,419 warheads deployed on
throughout a crisis or conflict.” The Biden Administration’s
662 missiles and bombers as of March 1, 2023, according to
2022 NPR argued that “maintaining a modern triad
a more recent State Department fact sheet. The State
possessing these attributes—effectiveness, responsiveness,
Department has stated that the United States “is prepared to
survivability, flexibility, and visibility—ensures that the
adhere” to the treaty’s central limits (1,550 deployed
United States can withstand and respond to any strategic
warheads on 700 deployed strategic launchers; 800 total
attack, tailor its deterrence strategies as needed, and assure
strategic launchers) “as long as it assesses the Russian
Allies in support of our extended deterrence commitments.”
Federation is doing so.”
Current Forces and Modernization Plans
Table 1. U.S. Strategic Nuclear Forces in 2022
Total
Deployed
ICBMs
System
Launchers
Launchers
Warheads
Before implementing the New START Treaty, the United
Minuteman III
454
396
396
States deployed 450 Minuteman III ICBMs at Air Force
ICBM
bases in Wyoming, Montana, and North Dakota. Under
New START, the number has declined to 400 deployed
Trident (D-5)
280
220
981
missiles, although the Air Force has retained all 450 silo
SLBM
launchers. While each Minuteman III missile originally
B-52 bombers
46
33
33a
carried three warheads, the United States deploys the
B-2 bombers
20
10
10a
missile with a single warhead in order to comply with New
Total
800
659
1,420
START levels. The Air Force has completed life extension
Source: U.S. Department of State. New START Treaty Aggregate
programs (LEPs) to improve the accuracy and reliability of
Numbers of Strategic Offensive Arms, September 1, 2022.
the Minuteman.
a. The treaty attributes one warhead to each deployed bomber,
The Air Force is also developing a new ICBM, the Sentinel,
although each could carry up to 20 bombs or cruise missiles.
previously known as the Ground-based Strategic Deterrent
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Defense Primer: Strategic Nuclear Forces
(GBSD), which will replace all Minuteman ICBMs. The
According to unclassified nongovernmental estimates, the
Air Force plans to acquire 659 missiles to support testing
United States has around 488 B61 and B83 gravity bombs.
and the deployment of 400 missiles. The NNSA is
NNSA is conducting an LEP on several variants of the B61
developing a new W87-1 warhead to deploy on the
to produce a single variant, known as the B61-12, which
Sentinel. For FY2025, the Biden Administration requested
began entry into the stockpile in 2022. DOD and NNSA
$3.7 billion for the Sentinel in the DOD budget and $1.1
have planned to retire the B83, the largest bomb remaining
billion for the W87-1 warhead in the NNSA budget. In
in the U.S. arsenal. The 2018 NPR supported retaining the
2024, DOD conducted a congressionally mandated review
B83, but the 2022 NPR announced retirement of the
of the Sentinel program due to cost overruns and delays.
weapon. In 2023, DOD announced that NNSA would
(See CRS In Focus IF11681, Defense Primer: LGM-35A
develop a new B61-13 bomb to give the President
Sentinel Intercontinental Ballistic Missile.) Some analysts
“additional options against certain harder and large-area
have argued that the ICBM leg in particular may be too
military targets” as it “works to retire” the B83.
costly to recapitalize or even unnecessary.
The Air Force is planning to replace the aging air-launched
SLBMs
cruise missiles carried by B-52 bombers with a new
advanced Long Range Standoff (LRSO) cruise missile. The
The United States currently has 14 Trident (Ohio-class)
Air Force plans to buy a total of 1,087 missiles and has
SSBNs. Under New START, each submarine carries only
included $834 million for the missile in its FY2025 budget
20, rather than the original 24, missiles. Using treaty
request. NNSA is also conducting an LEP on the W80
counting rules, the 14 submarines count as a total of 280
warhead to provide a warhead for the LRSO.
deployed and nondeployed launchers, with a maximum of
240 deployed launchers and around 1,000 warheads
Nuclear Command, Control, and Communications
counting on 12 operational boats (assuming two submarines
The United States is also modernizing its nuclear command,
are in overhaul). The Navy operates SSBN bases in
control, and communications (NC3) architecture consisting
Washington and Georgia.
of “warning satellites and radars; communications satellites,
aircraft, and ground stations; fixed and mobile command
The Navy is procuring 12 new Columbia-class submarines
posts; and … control centers for nuclear systems.” The
that feature 16 SLBM tubes each. The lead boat was
FY2025 budget request includes $11 billion for NC3.
supposed to enter service in 2031, but the Navy recently
stated that it is delayed by over a year. The Navy requested
Employment Planning and Force Sizing
$9.9 billion for the Columbia-class submarine in its
The U.S. President, the Secretary of Defense, the Chairman
FY2025 budget submission. (See CRS Report R41129,
of the Joint Chiefs of Staff, and other stakeholders in the
Navy Columbia (SSBN-826) Class Ballistic Missile
U.S. government and military participate in a process of
Submarine Program: Background and Issues for
planning for the potential employment of U.S. nuclear
Congress.)
forces that, inter alia, contributes to determining an
appropriate size and mix of U.S. strategic and nonstrategic
U.S. SSBNs carry the D-5 SLBMs. The Navy conducts Life
nuclear forces to meet U.S. national security requirements.
Extension Programs (LEPs) so that the missile remains
capable and reliable throughout the deployment of the new
The 2023 report of the Congressional Commission on the
Columbia-class SSBN. The Navy’s FY2025 budget request
U.S. Strategic Posture argued that the current U.S. nuclear
includes $2.5 billion for the D5LE and D5LE2 programs.
forces modernization plan (the so-called program of record,
NNSA has conducted an LEP for the W76 warhead, which
or POR) is “necessary, but not sufficient” because it does
is carried by most Trident missiles, and provided a small
not account for an emerging environment where the United
number of low-yield warheads, known as the W76-2, to the
States will face two nuclear peers—Russia and the People’s
Navy in FY2020. NNSA is also improving the safety and
Republic of China (PRC). (See CRS In Focus IF12621,
reliability of the W88 warhead, which is carried by a
Congressional Commission on the U.S. Strategic Posture.)
portion of the fleet, and has initiated work on the W93
warhead, which is to eventually deploy on D-5 missiles.
In 2024 testimony, Biden Administration officials have
stated that “the administration is prepared to further adjust
Heavy Bombers
the [POR] and the posture, readiness, and composition of
The Air Force has 20 B-2 bombers based in Missouri. The
nuclear forces if needed to sustain deterrence, assure allies,
B-2 bomber can carry B61 and B83 nuclear gravity bombs,
and achieve U.S. objectives if deterrence fails.” According
but it is not equipped to carry cruise missiles. The Air Force
to Administration officials, the President also updated the
maintains 76 B-52H bombers at bases in Louisiana and
U.S. nuclear employment guidance in 2024 to account for
North Dakota. The B-52 bomber, which first entered
PRC’s expanding nuclear weapons program “and the need
service in 1961, is equipped to carry nuclear air-launched
to deter Russia, the PRC, and North Korea simultaneously.”
cruise missiles (ALCMs). The B-2 and B-52 bombers can
also carry conventional weapons and participate in U.S.
This In Focus was originally authored by Amy F. Woolf,
conventional military operations. The Air Force also is
Specialist in Nuclear Weapons Policy.
acquiring a new B-21 Raider bomber for conventional and
nuclear missions; the service plans to “procure a minimum
Anya L. Fink, Analyst in U.S. Defense Policy
of” 100 of the new bomber, which is currently in testing
and initial production. The Air Force has included $5.3
IF10519
billion for this bomber in its FY2025 budget request.
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Defense Primer: Strategic Nuclear Forces
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