https://crsreports.congress.gov
August 8, 2024
U.S. Extended Deterrence and Regional Nuclear Capabilities
One of the stated goals of U.S. nuclear weapons policy is to
extend deterrence to over 30 U.S. “allies and partners” and
assure these countries that the United States will come to
their aid, including potentially by using U.S. nuclear
weapons, if they are attacked. The 2010, 2018, and 2022
Nuclear Posture Reviews (NPRs), which are periodic
assessments of U.S. nuclear policy, argued for
strengthening extended deterrence and posited that such
deterrence supported U.S. nuclear nonproliferation goals.
The 2022 NPR stated
Allies must be confident that the United States is
willing and able to deter the range of strategic
threats they face, and mitigate the risks they will
assume in a crisis or conflict.… Extended nuclear
deterrence contributes to U.S. non-proliferation
goals by giving Allies and partners confidence that
they can resist strategic threats and remain secure
without acquiring nuclear weapons of their own.
Congress authorizes and appropriates funds for, and
conducts oversight of, U.S. deterrence policies and their
implementation, as well as U.S. defense and other
cooperation with allies and partners.
Evolution of Extended Deterrence
Since the beginning of the Cold War, as part of its
participation in NATO’s collective defense commitment
enshrined in the 1949 North Atlantic Treaty, the United
States threatened to use military force, including the first
use of U.S. nuclear weapons, in response to an act of Soviet
armed aggression against Western Europe. Such limited
U.S. nuclear use carried the possibility of escalation to an
all-out nuclear war between the United States and the
Soviet Union; U.S. policymakers deemed this a credible
deterrent of potential Soviet attack. The United States also
eventually provided assurances to several allies in Asia that
it would back their security with U.S. nuclear weapons.
Since the late 1950s, successive U.S. Administrations have
expressed concerns about the security threats posed by the
possible proliferation of nuclear weapons. During the
negotiations on the Treaty on the Non-Proliferation of
Nuclear Weapons in the 1960s, several U.S. allies sought
additional U.S. security assurances while pledging that they
would not develop nuclear weapons. U.S. policy has thus
sought to extend the U.S. “nuclear umbrella” over allies in
Europe and Asia in part as a means to reduce the incentive
for them to acquire their own nuclear weapons.
Policymakers and experts in allied countries may debate the
extent to which U.S. official statements, capabilities, and
plans to defend them constitute a credible security
commitment. If an allied government doubts the U.S.
extended deterrence commitment, the government may
respond by requesting additional U.S. security assurances
or by improving its own perceived security through other
means. These means may include the development of
independent or cooperative nuclear weapons capabilities.
After the end of the Cold War, the United States reduced its
nuclear forces, including those stationed abroad, and
narrowed the range of contingencies for which the United
States would consider the first use of nuclear weapons. The
2010 and 2022 NPRs, which articulated a reduced role for
nuclear weapons in U.S. military planning, emphasized the
importance for extended deterrence of U.S. and allied
nonnuclear capabilities, such as theater missile defense, and
the forward presence of U.S. conventional forces. Allied
perceptions of U.S. security commitments may be sensitive
to U.S. domestic debates about possible shifts in U.S.
nuclear policy or posture.
U.S. Regional Nuclear Capabilities
During the Cold War, the United States deployed various
nonstrategic nuclear weapons, including capabilities that
later were eliminated as part of U.S.-Soviet arms control
and unilateral commitments, to allied countries. Today, the
United States extends deterrence to its allies through
forward-deployed nuclear weapons, U.S.-based aircraft
capable of conventional or nuclear missions that could be
deployed in a crisis, and strategic nuclear forces. (See CRS
In Focus IF10519, Defense Primer: Strategic Nuclear
Forces.)
The primary stated purpose of U.S. regional nuclear
deterrence capabilities is to deter the limited use of nuclear
weapons by Russia, the People’s Republic of China (PRC),
and North Korea, and those countries’ nuclear coercion of
U.S. allies and partners. Regional nuclear deterrence
systems include the following:
• Dual-Capable Aircraft (DCA), including those
operated by seven NATO allies as part of NATO’s
“nuclear burden-sharing.” The last three NPRs have
supported transitioning from the F-16 aircraft to the F-
35 Joint Strike Fighter. The Air Force is procuring the
F-35 jointly with some NATO allies and other U.S.
allies and partners. The DCA can carry the B-61
gravity bomb, which is deployed from some NATO
bases under U.S. operational control.
• The U.S. Navy deploys a low-yield variant of the W76
warhead (the W76-2) on the Trident II D5 submarine-
launched ballistic missile, as per a requirement
articulated in the 2018 NPR.
• In 2024, the U.S. Department of Defense (DOD)
initiated a program to procure a nuclear-armed sea-
launched cruise missile as per Section 1640 of the
FY2024 National Defense Authorization Act (P.L.
118-31). (See CRS In Focus IF12084, Nuclear-Armed
Sea-Launched Cruise Missile (SLCM-N).)
