SECRETARY OF DEFENSE
1000 DEFENSE PENTAGON
WASHINGTON. DC. 20301-1000



 

The Honorable Mitch McConnell
Majority Leader

United States Senate
Washington. DC 20510

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You recently received a letter from several former government of?cials regarding the
President?s request to lower the nuclear explosive yield of a small number of existing submarine
launched ballistic missile warheads As you know. the President requested this modest
adjustment to our nuclear capabilities to counter Russia's apparent belief that it could use its low
yield nuclear weapons to coerce the North Atlantic Treaty Organization or otherwise support
conventional aggression against US. allies and partners.

Critics ol'this approach argue that current US. nuclear forces and nuclear doctrine can
counter Russia?s limited nuclear use doctrine and tactical nuclear weapons. It is not possible to
determine precisely what is needed to deter with high con?dence. it is. however. possible to get
indications that one's deterrence strategy, posture, and capabilities are potentially inadequate.
Since the 2010 Nuclear Posture Review (N PR). Russia has increased the num her and diversity of
its "nuclear capabilities. continues to practice and exercise with these forces. and has issued veiled
nuclear threats against the United States, its allies. and partners. This suggests that Russia is
seeking ways to use nuclear weapons in support of its national security policy. and it suggests
that measures by the previous Administration to modernize our nuclear forces may not be
suf?cient to deter Russian aggression. North Korea has made similar, coercive nuclear threats.

Particularly in the casc of Russia. although it is true that the United States already has
low?yield capable nuclear weapons, these weapons must be delivered by aircraft. which are
vulnerable to formidable existing Russian air defenses. Russia may conclude that it can blunt the
current US. low-yield response and that the United States would be self-deterred from using
strategic nuclear weapons; the low-yield warhead dispels this notion however mistaken
it might be.

The authors of the letter argue that nuclear war cannot be controlled and that there is no
such thing as a limited nuclear war. Unfortunately, pcten?al adversaries have openly discussed
the bene?ts of limited nuclear employment. "therefore, effective U.S. deterrence requires
ensuring that potential adversaries do not miscalculate regarding the consequences of nuclear
first use. either regionally or against the United States itself. They must understand that there are
no possible bene?ts from non-nuclear aggression or limited nuclear escalation. The W762
warhead is meant to reinforce the credibility of our response. which strengthens deterrence by
denying potential adversaries the advantages they appear to believe they could realize from
nuclear ?rst use. It Sends a signal to Russia and other potential adversaries that, in the words oi"

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the authors of the letter, ?the United States is serious about maintaining an unambiguously strong
nuclear deterrent."

Finally,we gettothecruxoftheauthors? 
feel less restrained about using it in a crisis.? Let me be clear, any decision to employ nuclear
weapons would be the most di?icult decision a President has to make. This Administration, like
the ones before it, has said that nuclear weapons would be employed only in extreme
circumstances to protect our vital interests and those of our allies and partners. The W764
strengthens deterrence by raising the threshold to nuclear employment.

The 2018 NPR has received broad bipartisan support. The modernization of US. nuclear
forceswas previous Administra?onandwill continueoverthe nexttwentyyears.
The President?s request for the WG-2, a supplemental capability, is in response to developments
in Russian nuclear doctrine, exercises, and its new nuclear capabilities. While strengthening the
deterrence of attacks against the U.S.. allies. and partners. it does not require developing a new
nuclear warhead or nuclear testing, it does not violate any nuclear arms control treaty, and it does
not increase the size of the nuclear stockpile.

Nuclear modernization is affordable and is the number one priority of the Department of
Defense. Thank you for your continued support.



 



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