Stop the low-yield Trident nuclear warhead

On Tuesday,  the House Subcommittee on Strategic Forces debated the draft Fiscal Year 2020 National Defense Authorization Act. 

It voted out, on party lines, language that prohibits deployment of a low-yield warhead on the Trident D5 submarine-launched ballistic missile. That makes sense: The rationale for the warhead is dubious, and the weapon likely would never be selected for use.

The Trump administration’s 2018 Nuclear Posture Review called for a low-yield warhead on some Trident D5 submarine-launched ballistic missiles (SLBMs). The plan modifies a W76-1 warhead, which has an explosive yield of 100 kilotons — seven times the size of the weapon used against Hiroshima — to produce the W76-2, reportedly with a yield of “just” five-seven kilotons. 

Adding this weapon to the arsenal would risk lowering the nuclear threshold. To be sure, Pentagon officials assert that new low-yield weapons would not lower the threshold.

Yet the Nuclear Posture Review argued for low-yield weapons out of concern that Russia might feel it could use its “small” nuclear weapons free of concern about U.S. retaliation because the United States arsenal consists mainly of large-yield weapons. 

So, at a minimum, the goal of new U.S. low-yield nuclear weapons would appear to be to persuade Moscow that the United States is more likely to go nuclear. 

It is in the U.S. interest to maintain the highest possible threshold against the use of any nuclear arms. We should avoid steps that might signal, even inadvertently, that the use of “small” nukes is somehow acceptable. 

Moreover, the United States already has low-yield weapons and is modernizing them. Next year, serial production of the B61-12 nuclear gravity bomb will begin. That bomb, the result of a program costing $8-10 billion, supposedly has a variable yield range of 0.3 kilotons to 50 kilotons. 

Advocates of placing the W76-2 atop Trident SLBMs argue that the W76-2 could penetrate sophisticated air and missile defenses and reach its targets in minutes rather than hours. That’s true, but the U.S. military already is investing many tens of billions of dollars in the F-35 Joint Strike Fighter and B-21 bomber. 

Those aircraft are advertised as having stealth and advanced electronic warfare capabilities specifically designed to penetrate and defeat sophisticated air defenses. 

As for flight times, there may not be that much difference between minutes and hours for most non-strategic nuclear missions. That is especially the case in missions for which the primary purpose of delivering a low-yield warhead is to demonstrate U.S. resolve and try to arrest escalation rather than destroy a particular target.

Even if the W76-2 is deployed, would it ever be launched, even in a situation in which nuclear weapons had been used or were on the brink of use? 

SLBMs on submarines at sea constitute the most important and most survivable leg of the U.S. strategic triad, because the submarines can hide underwater and have lots of ocean in which to roam.  Each submarine at sea carries a significant portion of the survivable U.S. nuclear deterrent. 

The problem with launching an SLBM with a W76-2 is that it would reveal the submarine’s location. The submarine could maneuver away from the launch point, but it still would have compromised its general position, putting at risk the boat and the other 80-90 warheads it carried. Would the U.S. military run that risk, particularly given the availability of other low-yield options?

A bigger problem is discrimination. The Russians could not tell whether a launched SLBM carried a W76-2 or a W76-1 (100 kilotons) or, for that matter, a W88 (450 kilotons) until the weapon (or weapons) detonated.

The circumstances in which Washington might consider using a low-yield nuclear weapon against Russia or Russian military forces almost certainly would result from escalation of a conventional conflict. By far the most likely location for U.S.-Russia conventional conflict is the Baltic region in Europe. 

Assume a conventional NATO-Russia conflict in the Baltics, and Russia escalates by using a few “small” nuclear weapons. A decision to respond with a W76-2 would mean launching an SLBM from the Atlantic Ocean.

The problem is that a launch from many parts of the Atlantic toward the Baltics would also appear, at least initially, to be a launch against Moscow. 

Would the U.S. leadership launch a W76-2 — and run the risk that the Russians misread it as larger warhead intended to flatten Moscow in a decapitation strike — when F-35s and B61-12 bombs are available in Europe (as they will be in the early 2020s)? 

The W76-2 makes little strategic sense, could inadvertently lower the nuclear threshold and likely would never be used, even in the most dire circumstances. 

The Trump administration made a mistake by deciding to produce it. Congress should use the 2020 National Defense Authorization Act to correct that mistake and prohibit its deployment. 

Steven Pifer is a William Perry fellow at Stanford University’s Center for International Security and Cooperation.