March 21, 2019
A Low-Yield, Submarine-Launched Nuclear Warhead:
Overview of the Expert Debate
The Low-Yield D-5 Warhead
weapons after an adversary’s nuclear use in a regional
The Trump Administration is developing a new low-yield
conflict, and therefore could be coerced into withdrawing
version of the W-76 warhead for existing submarine-
from the fight if an adversary threatened nuclear use. They
launched Trident II (D-5) missiles. Unclassified sources
contend that Russia in particular might threaten to escalate
state that the current W76-1 warhead has an explosive yield
to nuclear weapons if it were losing a conventional conflict,
of around 100 kilotons. The National Nuclear Security
and note that Russia has exercised the use of low-yield
Administration (NNSA) has said the low-yield version, the
nuclear weapons for this type of contingency. They argue
W76-2, would be configured “for primary-only detonation.”
that if Russia pursued this approach, the United States
This could mean a yield of less than 10 kilotons.
would only be able to respond with the higher-yield
weapons like those currently deployed on submarine-
Congress appropriated $65 million for work on the W76-2
launched missiles. The deployment of a low-yield D-5
warhead in FY2019. According to NNSA, the first modified
warhead would therefore bolster deterrence by convincing
warhead was completed on February 22, 2019; the program
Russia that the United States could respond with a
is scheduled to complete the planned production run and
proportional, limited attack.
deliver the warheads to the Navy by late 2019. NNSA has
not disclosed the total number of planned W76-2 warheads,
Critics of the NPR’s analysis question whether the United
although it is expected to be a very small portion of the
States needs a new weapon to address Russia’s mistaken
W76 stockpile (estimated, in unclassified sources, to be
belief that it could threaten escalation without fearing U.S.
around 1,300 total warheads).
retaliation. If the belief is mistaken, they argue, then the
United States could respond by reasserting and reaffirming
The Trump Administration outlined its desire to produce a
its commitment to its allies in Europe, so that Russia would
low-yield version of the W76 warhead in the 2018 Nuclear
know that this type of threat would not be met with a U.S.
Posture Review (NPR). It cited the need for additional
or NATO retreat. They also contend that the deployment of
“tailored” and “flexible” capabilities to address the danger
new low-yield options could increase the risk of nuclear
of coercive nuclear use, a concept described below, by
war because their existence would make it easier for U.S.
Russia and North Korea. The NPR stated that this warhead
officials to consider the use of nuclear weapons in a
would supplement existing U.S. strategic nuclear
conflict. Some have also argued that there is no “gap” in
capabilities to “enhance deterrence by denying potential
capabilities because the United States already has low-yield
adversaries any mistaken confidence that limited nuclear
warhead options for gravity bombs and cruise missiles
employment can provide a useful advantage over the United
deployed on U.S. and NATO aircraft.
States and its allies,” and that low-yield warheads would
not add to the number of deployed SLBM warheads, but
On these latter points, those who support the NPR’s
would replace some “higher-yield [SLBM warheads]
analysis have pointed out that the low-yield SLBM offers
currently deployed.”
improved survivability and penetration because weapons
delivered by aircraft would be vulnerable to an adversary’s
The NPR report, and its argument in favor of a low-yield
air defenses. Some have also cited the U.S. experience of
SLBM warhead, launched a debate among U.S. experts
deploying lower-yield nuclear weapons during the Cold
about the rationale for the development of such a warhead
War to posit that there is no evidence that United States is
and the benefits and risks that might accrue from its
more likely to use these weapons just because it has them.
deployment. While some argue that this warhead is a
response to Russia’s so-called “escalate to de-escalate”
The Potential for Limited Nuclear War
strategy that will strengthen deterrence and raise the nuclear
The debate has also included discussions about whether a
threshold, others contend that it will lower the threshold for
war in which nations used small numbers of low-yield
U.S. use and increase the risk of nuclear war.
nuclear weapons could remain “limited,” or whether it
would inevitably escalate to a more extensive nuclear
Deterrence vs. Warfighting
exchange. The NPR’s analysis rests on the view that
The core of the debate over the low-yield D-5 warhead
Russian doctrine contemplates the limited use of nuclear
focuses on the question of whether the United States has a
weapons in a conflict where Russia is losing a conventional
gap in its current nuclear deterrent capabilities that can be
war, and that the United States needs to be able to threaten
filled by the deployment of a new low-yield warhead. The
a limited retaliatory attack to deter Russia. Critics of this
2018 NPR and experts who support the report’s assessment
analysis have countered that there is no such thing as
argue that adversaries might mistakenly believe the United
“limited” nuclear war because any use of a nuclear weapon
States would be self-deterred from responding with nuclear
would make a conflict something more than limited. Even if
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A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate
the numbers are small and the yields are low, they argue,
daunting search area, making it very difficult for Russia to
the damage would be extensive. They have also argued that
pinpoint the boat’s location with enough confidence to
nuclear war could not be controlled, so even the limited use
launch a successful attack.
of nuclear weapons would risk a global catastrophe.
Collateral Damage
Some analysts dispute the idea that nuclear war cannot
Considerations about a potential reduction in collateral
remain limited. Others, however, agree that the use of
damage have also entered into the debate about the
nuclear weapons would increase the risk of broader
development of low-yield SLBM warheads. The U.S.
escalation and see this as a point in favor of the U.S.
military has generally favored, based on the Law of Armed
deployment of low-yield nuclear weapons. They argue that
Conflict, providing the President with nuclear options that
Russia seems to believe that it could use nuclear weapons in
have “less collateral effect.” By extension, some experts
a limited way and deter the United States from responding
have posited the need for a “nuclear necessity principle,”
with its larger warheads. By deploying a low-yield SLBM
where U.S. nuclear planners would “use the lowest-yield
warhead, the United States would not only aim to convince
nuclear weapon possible,” and only in cases where
Russia that the United States would respond after a limited
hardened and buried targets could not be destroyed by
attack, but would also bolster deterrence precisely because
conventional weapons. A low-yield D-5 warhead, they
Russia’s limited use of nuclear weapons could lead to an
argue, would support this goal.
escalation to a broader nuclear exchange.
Others counter that the lower-yield warhead and less-
In disputing this analysis, some have questioned the NPR’s
stringent use parameters would actually increase the risk of
assessment of Russian nuclear doctrine and have countered
nuclear use in a conflict. This, they argue, would actually
that the NPR’s assertion that Russia has lowered its nuclear
increase the risk of nuclear war, and therefore increase the
threshold is not based on sufficient evidence. They argue
risk of devastating nuclear destruction, possibly in violation
that the possible first use of nuclear weapons by Russia and
of the Law of Armed Conflict.
North Korea would likely have less to do with a coercive
nuclear strategy intended to deter the United States than
with these countries’ concerns about U.S. conventional
Anya Fink provided valued assistance in preparing this report.
superiority—that they would resort to nuclear weapons
because they could not fight and win a conventional war.

The Discrimination Problem
CRS Products
Some experts have posited that the deployment of a low-
CRS Report RL33640, U.S. Strategic Nuclear Forces: Background,
yield SLBM warhead could create a new “discrimination
Developments, and Issues, by Amy F. Woolf
problem,” in which an adversary like Russia would be
unable to distinguish during a conflict if an SLBM launched

by the United States carried just one low-yield warhead and
was not part of a large attack. In this view, a U.S. launch
intended to control the escalation of a regional conflict
Other Resources
could contribute to Russia’s decision to escalate to the
U.S. Department of Defense, Nuclear Posture Review,
strategic level due to misinterpretation and doubts about its
Washington, DC, February 5, 2018.
early warning systems’ accuracy.
John R. Harvey, Franklin C. Mil er, Keith B. Payne, and Bradley
Others have disputed this assessment, arguing that the U.S.
H. Roberts, “Continuity and Change in U.S. Nuclear Policy,”
policy of “limited nuclear options” has historically been,
RealClear Defense, February 7, 2018.
and continues to be, based on assessments that Russia’s
Jon Wolfsthal, “Say No to New, Smaller Nuclear Weapons,”
early warning systems could tell the difference between a
War on the Rocks, November 22, 2017.
single launch and large attack. They contend that Russia
Francis J. Gavin, chair, “Policy Roundtable: The Trump
would likely delay its response until it had made that
Administration’s Nuclear Posture Review,” Texas National
assessment. They also claim that the novelty of this
Security Review, February 13, 2018.
“discrimination problem” is overstated because the United
Daryl Kimball and Kingston Reif, “The New U.S. Nuclear
Kingdom already deploys low-yield warheads on its
Strategy is Flawed and Dangerous. Here’s Why,” Arms
SLBMs, and the United States and United Kingdom rely on
a “common pool” of Trident II D5 missiles—
Control Association, February 15, 2018.
yet no one has
ever claimed that this arrangement might lead to confusion
Austin Long, “Discrimination Details Matter,” War on the
about the size or scale of a U.S. retaliatory attack.
Rocks, February 16, 2018, also Austin Long, “Location,
Location, Location,” Lawfare, March 11, 2018.
Submarine Vulnerability
Scott Sagan, “Armed and Dangerous,” Foreign Affairs,
Some have advanced the argument that U.S. ballistic
November 2018.
missile submarines could be vulnerable to detection after
the launch of a single or small number of missiles carrying

low-yield warheads because the launch would reveal the
boat’s location. Others have countered that the boat would
Amy F. Woolf, Specialist in Nuclear Weapons Policy
be able to move quickly enough to create a large, possibly
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A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate


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