There is no higher security requirement than deterring a nuclear attack against the U.S. homeland or our allies and partners. Today, the United States is in the early stages of comprehensively modernizing the nuclear forces to protect the United States from such an attack. Redeveloping a nuclear sea-launched cruise missile, or SLCM-N, is a vital component of our modernization plan.

Since the end of the Cold War, the U.S. reduced the size of its nuclear stockpile by over 80 percent. This includes a more than 90 percent reduction in weapons carried by theater and tactical — or “nonstrategic” — nuclear systems. The United States retired both the warheads and the systems that carried them, including the nuclear Tomahawk Land Attack Cruise Missile. The TLAM-N was deployed from 1983 to 1991 on surface ships and submarines before being retired in 2010. Unfortunately, Russia and China did not follow our example regarding this class of weapons, and are instead expanding their arsenals despite repeated U.S. overtures for negotiations.

Russia has approximately 2,000 “nonstrategic” nuclear weapons on a wide range of delivery platforms. These include nuclear armed torpedoes, depth charges, anti-ship missiles, anti-submarine missiles, gravity weapons, anti-aircraft missiles, ground-launched cruise missiles and short-range ballistic missiles. Russia has amassed this array of nuclear systems even though the comparable U.S. inventory only contains gravity weapons in quantities that are an order of magnitude less than Russia’s. Russia’s investment in and integration of these capabilities into its escalation doctrine and exercises raise the disturbing prospect that Russia perceives vulnerabilities in the current U.S. nuclear posture, exploitable by their “nonstrategic” nuclear arsenal during a crisis.

The SLCM-N is one of two supplemental capabilities recommended by the 2018 Nuclear Posture Review designed to address this risk. It accomplishes several goals. First, the SLCM-N demonstrates to adversaries that they cannot expect to conduct a limited nuclear attack without having to face the prospect of a U.S. nuclear response in kind or worse. The SLCM-N is not an attempt to match the size and diversity of the Russian nonstrategic nuclear arsenal. Rather, by providing the president with a wider range of credible response options, it strengthens deterrence of Russian nuclear use, however limited, in the first place.

Second, the SLCM-N assures allies in multiple theaters by providing or enhancing regional capabilities so important to our extended deterrence commitments. Importantly, the SLCM-N provides this assurance without exposing — or further exposing — allies to politically fraught basing decisions that potential adversaries will seek to exploit.

SLCM-N brings back significant advantages of TLAM-N to include the survivability of being deployed on either a covert, submerged platform, or spread out on several surface ships. Operating from highly survivable undersea platforms, SLCM-N will reinforce the credibility of tailored deterrent options in both Europe and East Asian contingencies. Sea-based systems can exploit an extensive operating area in which they will be difficult to find and destroy, preserving the ability to respond. In this way, SLCM-N will add to the flexibility and diversity of regional deterrence forces and provide an assured response capability in demanding operational environments.

Another timeless capability of SLCM-N is the gained advantage of having an in-theater, distributed surface fleet or submerged asset that provides the prompt response inherent in an ubiquitous system. SLCM-N provides the ability to strike a target quickly once the order to execute is received, removing time delays as a factor in a potential adversary’s decision-making calculus for limited nuclear weapon employment.

Critics, including Russia, will inevitably label the decision to procure the SLCM-N as the start of an “arms race,” but that charge is detached from reality. Rather than follow our lead and reduce the number and types of theater and tactical nuclear weapons, Russia is modernizing and expanding the full suite of its capabilities. The United States is looking to add a capability to fill a perceived gap in our deterrence posture.

The SLCM-N is a measured response to a growing threat and will be a crucial element to deterring the war that must never be fought. The deterrence effects it will provide are unique and essential to preventing adversarial nuclear attacks, which is the highest defense priority of the United States.

Vic Mercado is the assistant secretary of defense for strategy, plans and capabilities, and he is performing the duties of deputy undersecretary of defense for policy.

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