A few weeks ago — ok, maybe longer — I commented on an interesting proposal (that I nevertheless disagree with) by Crispin Rovere and Kalman Robertson to prohibit low yield nuclear weapons. I agued (“Size Doesn’t Matter“) that I didn’t agree with the problem as framed, didn’t think the treaty could be verified and, in any event, thought entry-into-force of the CTBT would be a better use of our time and energy.
Rovere and Robertson asked for the opportunity to respond, which I think is quite reasonable:
Size Matters
Crispin Rovere and Kalman A. Robertson
The following is our response to Jeffrey’s challenge to our study and its conclusions. We apologise for this taking some weeks, Crispin has been lost in the internet black hole of the DPRK for much of that intervening period, and has only just rejoined the technological landscape.
Jeffrey critiques our study in precisely the right way, asking what problem we are trying to solve, examining our proposed solution, and then comparing it to the possible alternatives. He posits that low-yield nuclear weapons are not uniquely dangerous, that a treaty prohibiting nuclear weapons with design yields below five kilotons would not be an effective way of dealing with them anyway, and that universalisation of the Comprehensive Nuclear Test Ban Treaty would achieve the desired result.
We shall frame our response to these arguments in precisely the way that Jeffrey so excellently presented them…
1. What problem are we trying to solve?
We are concerned about the perceived usability of nuclear weapons, and we argue that low-yield weapons are more ‘usable’, on aggregate, than other kinds of nuclear weapon. Unlike nuclear weapons of higher yields, low-yield weapons make nuclear conflict more likely by weakening the firebreak that separates conventional and nuclear war. As the yields of nuclear weapons approach those of conventional weapons, the probability of conventional conflict escalating to the nuclear level increases.
It is true, as Jeffrey argues, that in the case of the United States the retention of low-yield weapons within its arsenal may not greatly increase the probability of America conducting a nuclear first strike. This is due to America’s overwhelming conventional superiority, because the contingencies in which the United States would consider a nuclear strike are likely to require higher yield weapons (see pages 36-37 of the full study). Nevertheless, U.S. possession of low-yield weapons causes non-nuclear armed states to apprehend the risk of their use in counter-proliferating strikes and they may respond accordingly by developing their own nuclear arsenals. Indeed it is for these very reasons that low-yield weapons are utterly pointless for the U.S to possess, and yet they are distinctly dangerous for other states such as Pakistan and Russia to retain. It is therefore in America’s interests to support the restriction of these weapons in a multilateral framework – precisely where the proposed treaty comes in.
2. Does our proposal solve this problem better?
Jeffrey is concerned that “if the Russians build these things, they will do so not for deterrence but because they plan to use them.” If this is true, then Jeffrey is right – it doesn’t matter what treaty is in place because we’re all going to be in a nuclear war.
But this is not typically why states pursue low-yield weapons. Rather, low-yield weapons are sought principally in order to deter conventionally powerful rivals. In other words, they are designed specifically as first strike weapons, to be used against conventional forces. Jeffrey is sceptical of Pakistan’s claims to be developing low-yield artillery, but even if they aren’t, India apprehends that Pakistan’s nuclear doctrine incorporates first strike scenarios involving low-yield weapons and is responding on that basis.
On verification, Jeffrey states that ‘in order to verify that no state possesses nuclear weapons of a certain yield, very intrusive measures would be necessary’. That would be true if the aim was to eliminate the technological possibility that a nuclear-armed state possesses nuclear weapons of low yield. But this is not the role of adequate verification.
In any nuclear arms control agreement, adequate verification means that, if a nuclear-armed state commits a militarily significant violation, it will be detected in sufficient time for other parties to take action that will effectively neutralise any resulting military advantage. If any nuclear-armed state violates a treaty banning low-yield weapons, it gets at most a marginal discernible advantage, immediately neutralised by the higher yield weapons held by potential rivals and/or the legal mechanism of the treaty. Consequently, verification requirements are almost vanishingly small.
Indeed, there are many treaties in international law that achieve their objectives without intrusive verification mechanisms. This is for one obvious reason – there is nothing substantial to be gained through a violation. The Anti-Personnel Landmine Convention, the Convention on Cluster Munitions, and the Convention on Certain Conventional Weapons have all created effective bans and yet they do not have any intrusive verification measures. Conversely, the NPT has stringent verification requirements (by way of IAEA safeguards) because there is a great incentive for some states to pursue nuclear weapons and their clandestine acquisition has profound consequences for the security of others. A treaty prohibiting low-yield weapons sits firmly in the former category because any state that has them, or gives them up, also has larger strategic alternatives.
To explain why, we can take Jeffrey’s Russia example. In a conventional conflict with the United States, Russia may calculate that the use of a low-yield nuclear weapon would not result in escalation to the strategic level, and that the United States will instead respond in-kind with low-yield weapons of its own. This could arguably benefit Russia, as its nuclear forces are far more capable than its conventional forces vis-à-vis the United States. But if a treaty prohibiting low-yield weapons were in place, then not only would such an attack be condemned by the international community, Russia would also be aware that America’s only option for retaliation would be to escalate. This understanding would no doubt factor seriously into the Russian calculus when deciding whether to cross the nuclear threshold in the first place. In other words, a treaty prohibiting low-yield weapons strengthens America’s nuclear deterrent, irrespective of whether Russia cheats by developing low-yield weapons.
It is through this lense that the verification issue must be viewed. Jeffrey makes the clever quip about “Frank Miller’s head exploding when he learns that we’re going to let the Russians examine all the electronics in our nuclear weapons.” Of course that’s not what we recommend, we simply say that any verification measures specifically for existing variable-yield weapons will depend on the electronics, and this may be the subject of separate negotiations between the states that possess them. For the reasons articulated above, the verification requirements are going to be modest, and will really depend on whether a state may have confidence that parties to the treaty aren’t deliberately fielding weapons that are specifically designed for nuclear first strike against conventional forces.
It is reasonable to assume that many thermonuclear weapons in advanced arsenals have primaries that, if they could be separately detonated without boosting, would result in a low-yield explosion (because such primaries tend to contain relatively small quantities of fissile material). This is an integral part of the physics of thermonuclear weapons and in this sense “swapping hydrodynamic codes”, to use Jeffrey’s expression, would indeed be worse than useless as a verification measure.
The fact that a state may have the capacity to detonate the unboosted primary of an otherwise high-yield weapon, such as an SLBM, to produce a low-yield nuclear explosion is unlikely to be a significant issue since no state could use it to deter a conventional attack without also openly violating the treaty.
3. …than other, more likely outcomes? (such as entry-into-force of the Comprehensive Nuclear Test Ban Treaty)
Leaving aside the question of whether it is more likely or not, Jeffrey’s assertion is that universalisation of the CTBT would more effectively deal with the problems we seek to solve than the treaty we propose. Although Jeffrey is right to point out the importance of the CTBT, and makes a good recommendation regarding confidence building measures at old Russian and US test sites, we must respectfully disagree with his assessment that the CTBT can substitute for a treaty prohibiting low-yield weapons.
To revisit the beginning, the problem we are trying to solve is as follows: to ensure the firebreak that exists between conventional and nuclear war is not undermined by the proliferation of low-yield weapons. The CTBT does not meet this objective.
Nevertheless, both a treaty prohibiting low-yield weapons and the CTBT multilateralise the arms control process in a manner that allows continued progress to be made on other arms control initiatives. Our proposed treaty actually makes the universalisation of the CTBT easier to achieve because it reduces incentives to test new low-yield designs. There is no reason why these two initiatives should not be pursued together, and we have previously written on the imperative of securing entry into force of the CTBT here, and here.
Jeffrey begins his critique of our proposed treaty by saying “it’s probably a bad idea”, but nothing in his argument actually suggests that it is. At most, he argues that it isn’t worth the political effort required, and on that point we differ, since taking non-strategic nuclear weapons into account in a multilateral framework is almost certainly a requirement for continued progress on nuclear arms control elsewhere.
We welcome the discussion that this proposal has generated, for it draws attention to the specifics of low-yield weapons in the broader arms control discourse. We believe that the introduction of low-yield weapons into unbalanced and unstable strategic rivalries carries greater risks of nuclear conflict than strategic weapons, which hitherto dominated nuclear arms control.