I’ve been meaning to write something on my objections to a proposal by Crispin Rovere and Kalman Robertson to ban low-yield nuclear weapons.

Now, I should say that I think developing low-yield nuclear weapons seems like a pretty terrible idea. I am not much of a fan of what used to be called “plywood” (precision low-yield nuclear warheads) and bemoaned the loss of the admittedly flawed Spratt-Furse Amendment. (Although you should totally ask me about the Golan Lumber Company some time.) But I am not sure that a treaty banning nuclear weapons with yields of below five kilotons is a workable solution to the threat posed by so-called non-strategic nuclear weapons.

Rovere and Robertson present the proposal in a ”new ASPI Insight paper, and in a longer companion study,” as well as a presentation Rovere made at  CSIS PONI meeting.  Rovere and Robertson have also hosted a discussion on the ASPI blog, with an outline of the proposal and exchanges with Malcom Davis (Davis|Rovere and Roberston|Davis again) and Rod Lyons  (Lyons|Rovere and Robertson).

I don’t find the proposal very compelling.  In fact, I think it’s probably a bad idea.  But I didn’t want to write anything until I thought I could be constructive.  Hey, there is a first time for everything!

The short version of my argument is that the nuclear weapons most likely to be used have yields in excess of the treaty’s five kiloton threshold, the treaty is so unverifiable that it will amount of a meaningless political commitment that no one takes seriously and that a much better solution to the development of “more usable” nuclear weapons would simply to bring into force the Comprehensive Nuclear Test Ban Treaty

The long version is after the jump.

Let’s step back and ask two questions: First, what problem are we trying to solve?  Second, does Rovere and Robertson’s proposal solve this problem better than other, more likely outcomes such as entry-into-force of the Comprehensive Nuclear Test Ban Treaty?


What problem are we trying to solve?

Rovere and Robertson start from the premise that nuclear weapons with yields below about five kilotons pose a “unique threat to international security.”  If I understand them correctly, they believe that low-yield nuclear weapons are, or will be, more usable in some fashion.  If we eliminate these weapons, we eliminate the most likely pathway to a general nuclear exchange.   (There are other concerns relating to proliferation and theft that seem to be of secondary importance.)

I think this is wrong.  In terms of utility, all things being equal, it is easier to use a smaller warhead against a target than a larger one.  But all other things are not equal.  Yield is a secondary factor in terms of utility.  Consider the US program to develop a Robust Nuclear Earth Penetrator.  RNEP would have been one of the most powerful warheads in the US arsenal, with a yield of up to one megaton — all the better to crush underground bunkers with, my dearie. The most “usable” weapons are the ones that can blow up targets.  That means yields significantly larger than what was unleashed on Hiroshima and Nagasaki.  Rovere and Robertson mention the 2001 Nuclear Posture Review, which expressed interest in weapons with “lower yields.” Notice that says  lower yields, not low yields. No one in the United States is suggesting dropping sub-kiloton firecrackers on Fuhrerbunkers, the early-1990s insanity about PLYWD notwithstanding.  IN case there was any confusion about that, our friend Linton Brooks cleared up:

This is a nuclear weapon. This is a nuclear weapon that is going to be hugely destructive and destructive over a large area. No sane person would use a weapon like that lightly, and I regret any impression that anybody, including me, has given that would suggest that this is going to be any easier a decision — I mean if this weapon were in the arsenal today, it would still be a hugely difficult decision for any president to even contemplate it. So I — the administration believes and I personally believe that this study should continue, but … I do want to make it clear that any thought of sort of nuclear weapons that aren’t really destructive is just nuts.

I general, I don’t think “low yield” nuclear weapons are more worrisome than other nuclear weapons — with the possible exception that the Russians might build something really, really irresponsible. I am actually quite skeptical that any country is, at the moment, stockpiling weapons with yields below five kilotons.  There are a few exceptions worth mentioning.

First, I am skeptical of Pakistani claims to be developing nuclear artillery.

Second, there are some people who believe the Russians might be interested in developing nuclear weapons with yields below a kiloton. If Russia were building lots of artillery-fired atomic projectiles (AFAPs) or other low yield weapons, then I would almost certainly agree that we should discuss why that’s a bad idea.  But I don’t think the evidence on Russian activities at NZ supports this hypothesis.  We’ll come back to this.

Third, some US thermonuclear nuclear weapons contain a “variable yield” or “dial a yield” option to detonate at ”the full yield of the two-stage weapon, the yield of the boosted primary, or the yield of the unboosted primary explosion.” Notice how I just quoted Dick Garwin there?  We’ll come back to this, too.

I general, I don’t think “low yield” nuclear weapons are more worrisome than other nuclear weapons.  In principle, man-portable nuclear weapons or nuclear artillery would be very worrisome.  In practice, however, neither state is building these sorts of weapons.


Does Rovere and Robertson’s proposal solve this problem better … 

Now, obviously, if Russia is developing sub-kiloton nuclear weapons, that might be something we’d worry about.  The problem is that I don’t know how we would verify Russia’s compliance with the treaty.

Rovere and Robertson tend to view verification as relatively unimportant because there are few deterrent benefits from a covert arsenal of low-yield nuclear weapons, as opposed to an overt one.  I worry, on the other hand, that if the Russians build these things, they will do so not for deterrence but because they plan to use them. (Recall that, in the Cuban Missile Crisis, we did not know there were Soviet nuclear weapons already in Cuba. That would have been a very nasty surprise.)

In order to verify that no state possesses nuclear weapons of a certain yield, very intrusive measure measures would be necessary. The United States and Russia possess many, many, many nuclear weapons designs with yields below 5 kilotons they could deploy without further testing.  The states party are simply not going to exchange the details of these designs nor allow inspectors to verify the design-types currently deployed.  The US and Russia can’t agree to count warheads stored at bomber bases, let alone swap hydrodynamic codes.  The entire endeavor of figuring out how to count actual warheads in a treaty is about protecting precisely the information necessary to verify a yield threshold. See the UK-Norway Initiative and the Princeton effort.

These comes through when Rovere and Robertson confront the problem of variable-yield warheads — thermonuclear warheads in which the yield of the primary is smaller than the full yield of the weapon:

Mechanisms for verifying the removal of low-yield settings from variable yield  weapons will depend on the electronics used in these weapons and may be separately  negotiated between the states that possess them.

That sound you hear is Frank Miller’s head exploding when he learns that we’re going to let the Russians examine all the electronics in our nuclear weapons.

When pushed, Rovere and Robertson entertain the idea of a completely verification-free political commitment:

 If this proved impracticable then a simple agreement never to use or threaten to use nuclear weapons on yield settings below the minimum-yield threshold, coupled with an undertaking to phase out existing stockpiles as they approach the end of their ordinary replacement timeline, could be sufficient.

This doesn’t really solve the problem since the lowest yield setting is an integral part of the nuclear weapons design.  We aren’t going to stop designing small primaries, although I suppose we could promise the Russians that the AFF set won’t have a dial-a-yield option.  Still, they’ll have to take our word for it.

Rovere and Robertson mention the  Spratt Furse Amendment, which prohibited the development of certain low-yield nuclear weapons.  Spratt-Furse contained a large number of exceptions that permitted research on low yield nuclear weapons such as the development of new primaries.  

Although I think the Bush Administration was wrong to seek repeal of Spratt-Furse, any prohibition on low-yield nuclear weapons by necessity had to legislate intention. The result was, as Linton Brooks complained, Spratt-Furse “leads us to the situation in which in addition to physicists and engineers, we have to have lawyers in thinking about technical development.” Now, I wasn’t terribly sympathetic to the nation’s weaponeers for the inconvenience they suffered, but Spratt-Furse was a difficult creature. In a treaty context, we would need a much better model than Spratt-Furse.


… than other, more likely outcomes?

(such as entry-into-force of the Comprehensive Nuclear Test Ban Treaty)

If the problem really is that the Russians are conducting hydronuclear tests at Novaya Zemlya in order to develop sub-kiloton tactical nuclear weapons, there is a much easier solution than an unverifiable treaty to ban low-yield nuclear weapons.  (After all, the crux of the problem is that we worry the Russians are already cheating on the CTBT.)

Why not simply work with Russia to bring into force the Comprehensive Nuclear Test Ban Treaty and, perhaps, agree to a set of confidence building measures to increase transparency at our test sites surrounding subcritical and hydrodynamic testing? (And don’t forget the Chinese!) This is a point that I’ve made over and over again.

Such an effort would be far from politically painless, but its a garden party compared to the nightmare of negotiating a global Spratt-Furse agreement.