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Updated December 14, 2022
Defense Primer: Strategic Nuclear Forces
The Nuclear Triad
launch a disarming first strike and to retaliate if such an
Since the early 1960s, the United States has maintained a
attack were attempted, and heavy bombers could be
“triad” of strategic nuclear delivery vehicles. These include
dispersed quickly and launched to enhance their
long-range land-based intercontinental ballistic missiles
survivability, and they could be recalled to their bases if a
(ICBMs), long-range submarine-launched ballistic missiles
crisis did not escalate into conflict.
(SLBMs), and long-range heavy bombers equipped to carry
The United States has reaffirmed the value of the nuclear
nuclear-armed cruise missiles and gravity bombs. The
triad. The Obama Administration noted, in the 2010
number of nuclear warheads carried on these delivery
Nuclear Posture Review (NPR), that the unique
vehicles peaked in the late 1980s, at around 14,000
characteristics of each leg of the triad were important to the
warheads. It has been declining ever since, both as the
goal of maintaining strategic stability at reduced numbers of
United States complies with limits in U.S.-Russian arms
warheads. It pointed out that strategic nuclear submarines
control agreements and as it has changed requirements after
(SSBNs) are the most survivable leg of the triad, that
the Cold War. As of February 2018, the United States had
single-warhead ICBMs contribute to stability and are not
reduced its forces to comply with the New START Treaty,
vulnerable to air defenses, and that bombers can be
which entered into force in early 2011. Table 1 displays the
deployed as a signal in crisis, to strengthen deterrence and
U.S. forces that counted under the treaty limits, as of
provide assurances to allies and partners. It also noted that
September 1, 2020. These forces fall below the treaty limits
“retaining sufficient force structure in each leg to allow the
of 1,550 deployed warheads on 700 deployed missiles due
ability to hedge effectively by shifting weight from one
to maintenance schedules and operational requirements.
Triad leg to another if necessary due to unexpected
Table 1. U.S. Strategic Nuclear Forces Under New
technological problems or operational vulnerabilities.”
START
The Trump Administration also reaffirmed the U.S.
Total
Deployed
commitment to the nuclear triad and to the modernization
System
Launchers
Launchers
Warheads
programs for each of the components of that force structure.
Minuteman
The 2018 NPR notes that “the triad’s synergy and
454
397
397
III ICBM
overlapping attributes help ensure the enduring
Trident
survivability of our deterrence capabilities against attack
280
230
1,012
(D-5) SLBM
and our capacity to hold a range of adversary targets at risk
throughout a crisis or conflict. Eliminating any leg of the
B-52
46
36
36a
triad would greatly ease adversary attack planning and
bombers
allow an adversary to concentrate resources and attention
B-2 bombers
20
12
12a
on defeating the remaining two legs.” The Biden
Total
800
675
1,467
Administration’s 2022 NPR supports continuing
Source: U.S. Department of State. New START Treaty Aggregate
investments in the modernization programs for all three legs
Numbers of Strategic Offensive Arms, December 1, 2020.
of the triad.
a. The treaty attributes one warhead to each deployed bomber,
Current Forces and Modernization Plans
although they could carry up to 20 bombs or cruise missiles.
The United States is recapitalizing each leg of its nuclear
b. A 2022 update says only that the United States had 1,420
triad and refurbishing many of the warheads carried by
warheads deployed on 659 missiles and bombers, as of
those systems.
September 1, 2022.
ICBMs
Rationale for the Triad
Before implementing the New START Treaty, the United
Early in the Cold War, the United States developed these
States deployed 450 Minuteman III ICBMs at three Air
three types of nuclear delivery vehicles, in large part
Force bases: F.E. Warren AFB in Wyoming, Malmstrom
because each of the military services wanted to play a role
AFB in Montana, and Minot AFB in North Dakota. Under
in the U.S. nuclear arsenal. However, during the 1960s and
New START, the number has declined to 400 deployed
1970s, analysts developed a more reasoned rationale for the
missiles, although the Air Force has retained all 450 silo
nuclear triad. They argued that these different basing modes
launchers. While each Minuteman III missile originally
had complementary strengths and weaknesses that would
carried three warheads, each now carries a single warhead,
enhance deterrence and discourage a Soviet first strike. For
both to reduce U.S. forces to New START levels and to
example, ICBMs were believed to have the accuracy and
adopt what is considered a more stabilizing posture.
prompt responsiveness needed to attack hardened targets
The Air Force has completed several programs designed to
such as Soviet command posts and ICBM silos, SLBMs had
improve the accuracy and reliability of the Minuteman fleet
the survivability needed to complicate Soviet efforts to
and to “support the operational capability ... through 2030.”
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Defense Primer: Strategic Nuclear Forces
The Air Force is also developing a new ICBM, the Ground-
first entered service in 1961, is equipped to carry nuclear or
based Strategic Deterrent (GBSD), which will replace all
conventional air-launched cruise missiles (ALCMs). The B-
missiles and ground launch control facilities. It plans to
52 bombers can also deliver a wide range of conventional
acquire 642 missiles to support testing and the deployment
arms, and are currently receiving numerous upgrades to
of a force of 400 missiles. The Air Force expects the
their communications and electronics systems. The Air
program to reach its initial operational capacity, with 9
Force is also acquiring a new B-21 bomber, for both
missiles on alert, by 2029; it expects to complete the
conventional and nuclear missions. It hopes to field
deployment, with 400 missiles on alert, in 2036. The Biden
between 80 and 100 of the new bombers, with the first to
Administration has included $3.6 billion for the program in
enter service around 2025. The Air Force has included $5
its FY2023 budget request.
billion for this bomber in its FY2023 budget request.
The National Nuclear Security Administration (NNSA), a
According to unclassified estimates, the United States has
semi-autonomous agency in the Department of Energy, is
around 475 B61 and B83 bombs. Several variants of the
working on a new warhead—known as the W87-1—that
B61 bomb are undergoing a life extension program (LEP),
will deploy on the new GBSD missile.
to enhance the bomb’s safety, security, and use control
SLBMs
features. This program will produce a single variant, known
as the B61-12, which will deploy with a new tail kit. This
The United States currently has 14 Trident (Ohio-class)
will replace the parachute currently used to slow the
ballistic missile submarines, with 2 in overhaul and 12 in
bomb’s descent and will improve its accuracy. NNSA
the operational fleet. Under New START, each submarine
estimates that the B61 LEP will cost nearly $9 billion, with
carries only 20, rather than the original 24, missiles. Using
an additional $1-$2 billion in Air Force funding for the new
treaty counting rules, the 14 submarines count as a total of
tailkit. The new model is expected to begin to enter the
280 deployed and nondeployed launchers, with a maximum
force in 2022. NNSA had planned to retire the B83, the
of 240 deployed launchers and around 1,000 warheads
largest bomb remaining in the U.S. arsenal, around 2025,
counting on the 12 operational submarines. The Navy
after the completion of the B61 LEP. The 2018 NPR
operates two bases for these submarines—one in Bangor,
supported plans to retain the B83, but the 2022 NPR also
WA, and one in Kings Bay, GA.
announces retirement of the weapon.
The Navy plans to begin retiring Ohio-class submarines in
The Air Force is planning to replace the aging air-launched
2027, with the new Columbia-class submarine expected to
cruise missiles carried by B-52 bombers with a new
begin entering the fleet in 2031. The Navy has recently
advanced Long Range Standoff (LRSO) cruise missile.
indicated that the fleet of 12 new submarines will cost $139
According to the Air Force, the existing ALCM has been
billion. It has requested $6.3 billion for the Columbia-class
through several life extension programs and is beginning to
submarine in its FY2023 budget.
show reliability problems. Reports indicate that the Air
Force plans to buy a total of 1,000-1,100 LRSO missiles, at
The Navy purchased over 530 D-5 missiles to support the
a cost of around $10.8 billion. It has included $1 billion for
Trident fleet. It has pursued a life-extension program for the
the missile in its FY2023 budget request. NNSA is also
missiles, funded at about $1 billion per year, so that they
conducting a life-extension program on the W80 warhead to
will remain capable and reliable into the deployment of a
provide a warhead for the new LRSO.
new, Columbia-class submarine. It has also initiated a
second life extension program for these missiles, known as
CRS Products
the D5LE II, and has included $173 million in its budget
request for FY2023.
CRS Report R41219, The New START Treaty: Central Limits and
Key Provisions, by Amy F. Woolf
NNSA is also working to extend the life of the warheads
CRS Report RL33640, U.S. Strategic Nuclear Forces: Background,
carried by U.S. SLBMs. It has conducted a life extension
Developments, and Issues, by Amy F. Woolf
program (LEP) for the W76 warhead, which is carried by
most Trident missiles, and provided a small number of low-
yield warheads, known as the W76-2, to the Navy in late
2019. NNSA is also altering the W88 warhead, which is
carried by a portion of the fleet, to address concerns with its
Other Resources
safety and reliability. In particular, the program will replace
DOD. Nuclear Posture Review Report. April 2010.
the aging arming, fuzing, and firing components. It has also
State Department. New START Treaty. April 2010
initiated work on the W93 warhead, which will eventually
deploy on D-5 missiles.
Heavy Bombers
This In Focus was originally authored by Amy F. Woolf,
The Air Force has 20 B-2 bombers, based at Whiteman
Specialist in Nuclear Weapons Policy.
AFB in Missouri. The B-2 bomber can carry both B61 and
B83 nuclear bombs, but it is not equipped to carry cruise
missiles. It can also carry conventional weapons and has
Paul K. Kerr, Specialist in Nonproliferation
participated in U.S. military campaigns from Bosnia to Iraq.
IF10519
The Air Force maintains 76 B-52H bombers at two bases,
Barksdale, LA, and Minot, ND. The B-52 bomber, which
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Defense Primer: Strategic Nuclear Forces
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