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Commentary: The US doesn't need new low-yield nuclear weapons

27 June 2019

A partisan battle in Congress over funding a new warhead program points to fundamental disagreements on the role of nuclear weapons.

Trident II D5 missile launch test.
An unarmed Trident II D5 missile launches from the USS Nebraska submarine off the cost of California in 2008. Credit: US Navy

As the only nation to have used nuclear weapons in anger, the US should be at the forefront of an urgent effort to eradicate them from the globe. Instead, the Trump administration is following the lead of Russian president Vladimir Putin by expanding the circumstances under which they could be used.

The fiscal-year 2020 defense authorization bill under consideration in the Republican-majority Senate includes $19 million to deploy a low-yield modification of the strategic W76 warhead, which tops most submarine-launched Trident II missiles. In its version of the defense bill, the Democrat-controlled House Armed Services Committee denied funds to deploy the warhead. (All but two committee Republicans voted to deploy the new weapon.) The House-passed FY 2020 defense appropriations bill also provided no funding for deployment.

Though the outcome of that conflict will be determined by the compromise to be worked out in a House–Senate conference committee in the coming weeks, the National Nuclear Security Administration has been manufacturing the low-yield warhead since February. Experts say that converting the 100-kiloton W76 to the low-yield version is accomplished by removing or disabling the weapon’s secondary, far more powerful stage.

According to the Trump administration’s 2018 nuclear posture review, the US needs more low-yield options to counter Russia’s purported “escalate to de-escalate” conflict strategy. The Russian doctrine, the review states, envisions striking the West with a low-yield nuke early in a conflict, on the assumption that the US, having only high-yield weapons in its inventory, would be reluctant to return fire. In theory, the US and its allies would then capitulate to Moscow’s demands. Trump’s military strategists reason that producing low-yield, less destructive weapons in the US might cause the Kremlin to rethink that war plan.

Many scholars doubt the existence of such a Russian nuclear strategy. Furthermore, the US has long deployed low-yield bombs. Although there is no standard definition for low yield, such weapons are generally regarded as those that produce a maximum of 15 to 20 kilotons—the respective yields of the Hiroshima and Nagasaki bombs. There are roughly 150 B61s deployed in NATO-member countries, each with an adjustable explosive force of 0.3 kilotons or more, according to an April update of US nuclear forces by Hans Kristensen and Matt Korda of the Federation of American Scientists. The US Air Force has about 500 nuclear-tipped air-launched cruise missiles that offer variable yields as low as 5 kilotons, they say.

The Trump administration’s nuclear posture review also argues that the new low-yield weapons would allow the US to respond proportionately to a nuclear provocation and do so without the need to seek approval from the countries that host B61s. The Pentagon has additional plans to acquire a new low-yield submarine-launched cruise missile, purportedly to address the same supposed Achilles’s heel of US nuclear deterrence. A previous generation of nuclear-tipped cruise missiles was removed from subs in 2011.

Altering a W76 warhead.
Technicians at the National Nuclear Security Administration’s Pantex Plant make adjustments to a W76 warhead. Credit: NNSA

But what happens if the new low-yield weapons don’t succeed in deterring a Russian low-yield attack? Or what if the US decides to preemptively launch a low-yield weapon during a conflict? Russia may not be able to determine whether an incoming US W76 is carrying a high- or low-yield business end. If the missile is assumed to be the more powerful strategic version, the situation could escalate into a full-blown intercontinental exchange.

The idea that a nuclear conflict, whether with low- or high-yield nukes, could be limited to a single exchange is questionable at best. And there is a danger that this sort of thinking, plus the prospect of fewer casualties, would lower the threshold at which the US would decide to go nuclear.

That bar had been raised significantly by the 1987 Intermediate-Range Nuclear Forces Treaty (INF), which prompted the US and the Soviet Union to eliminate nearly 2700 ground-based and cruise missiles in Europe having a range of 500–5500 kilometers. But both countries recently announced that they are abandoning the INF. The US says Russia has been in violation of the treaty since 2012, when it began testing a new ground-based cruise missile. According to the posture review, Russia currently has about 2000 tactical nuclear weapons, including antiship, antiaircraft, ground-launched, and air-launched missiles, torpedoes, bombs, and depth charges. Arrayed against that arsenal, the Pentagon says, the US has only the B61.

At various times during the past two decades, the defense establishment and the national labs have proposed new types of nukes to address various perceived needs, including a bunker buster. Each time, there was resistance from Congress, and the plans were dropped. The US hasn’t produced a new nuclear warhead since 1991.

Technically, the US still isn’t producing new warheads, since the low-yield variants are being taken from the inventory of deployed high-yield W76s. But such conversions wouldn’t have been allowed under the previous administration’s nuclear policy. In his 2010 nuclear posture review, President Obama formally renounced all new weapons development and directed that the refurbishment of existing warheads not add new military missions or capabilities.

Obama’s stricture was apparently open to interpretation, however. The replacement of a key W76 targeting component during a refurbishment campaign completed last year dramatically upgraded confidence that a single warhead could destroy a Russian missile in its hardened silo. That new assurance freed warheads that had been doubled up on the same target to be aimed elsewhere. The Pentagon’s own documents described the new component as having added “an efficient hard target kill capability.”

An upcoming $7.6 billion B61 life extension program planned during the Obama years will transform it to the first-ever guided nuclear bomb, as it’s outfitted with a new, steerable tail fin. If the improvement to its accuracy limits civilian casualties, that could be a good thing. But that could also result in a further lowering of the threshold for its use.

The Trump administration has shown a willingness to enlarge the role of nuclear weapons beyond strategic deterrence. Thankfully, the president and other top officials have said in recent months that they have begun to think about negotiating a follow-on to New START, the 2011 treaty that cut by 30% the number of warheads the two nuclear superpowers have pointed at each other, to 1550 apiece. The treaty expires in February 2021. If a new pact can be worked out, it would at least keep a lid on that number.

Editor’s note, 3 July: An earlier version of this article mischaracterized the prohibition on the W76 contained in the House defense authorization bill. The measure denies funding for the Navy to deploy the low-yield weapons, not funding for the National Nuclear Security Administration to convert the warhead.

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