Low Yield Nuclear Weapons, Earth Penetrating Warheads, and Tailored Deterrence

Recently the question of low yield nuclear weapons made a bit of a splash, as it has done from time to time from the 90s on to today. Analysts, in my view, are too fixated on the question of nuclear yield. Yes, this is important, but not enough emphasis is placed upon the matter of earth penetration capabilities.

The Defense Science Board, which kicked off the latest round of discussion, in December 2016 produced a paper on future defence priorities, and the section on nuclear weapons and nuclear deterrence caught quite a lot of attention. Most especially this passage;

A more flexible nuclear enterprise that could produce, if needed, a rapid, tailored nuclear option for limited use should existing non-nuclear or nuclear options prove insufficient

Notice that this is consistent with the remit of the Trump administration’s Nuclear Posture Review

The Secretary shall initiate a new Nuclear Posture Review to ensure that the United States nuclear deterrent is modern, robust, flexible, resilient, ready, and appropriately tailored to deter 21st-century threats and reassure our allies

Tailored deterrence was quite a popular concept during the Bush era, and it underpinned Bush’s own Nuclear Posture Review in my opinion. I wrote a lot about that at the time. One of the things the Bush administration wanted to develop was the Robust Nuclear Earth Penetrator. The idea, of a new earth penetrating nuclear weapon, had important antecedents, especially in the Clinton administration.

Now very good things have been said in very good analysis about the Defense Science Board report and low yield nuclear weapons by Michael Krepon and Philip Coyle, amongst others. I don’t disagree with the points made in these, important, analyses. But I feel they deemphasise the question of earth penetrating nuclear weapons.

It, correctly, is pointed out that the B61 and various of its modifications have dial-a-yield options, including a 0.3 Kiloton option. But the B61-12, the latest modification developed through the Stockpile Stewardship based Life Extension Programme, has an earth penetrating capacity.

During the Clinton administration advocates of a new earth penetrating nuclear weapon spoke of it as being a low yield earth penetrating weapon. The plan with the RNEP, however, was to use the B83 bomb as its basis, which had a yield of 1.2 megatonnes which is hardly low. That said, however, the B83 did have dial-a-yield options ranging from low kilotons up to 1.2 megatonnes, and it may well also, in part, have had a similar physics package to the B61. So the RNEP could well have also been used as a low yield earth penetrator.

Very recently an F-16 dropped a B61-12 in a mock, non-nuclear components, bombing run. In very good analysis, Hans Kristensen of the Federation of American Scientists, demonstrated that the B61-12 has an earth penetrating capacity

This is very important as Kristensen, correctly, stated,

The evidence that the B61-12 can penetrate below the surface has significant implications for the types of targets that can be held at risk with the bomb. A nuclear weapon that detonates after penetrating the earth more efficiently transmits its explosive energy to the ground, thus is more effective at destroying deeply buried targets for a given nuclear yield

The two, low yield and earth penetration, it is my hunch, go together when it comes to tailored nuclear weapons. Analysts need to consider both, I tend to think.

But why emphasise earth penetration?

Because tailored deterrence is code for intra-war deterrence. The object is to develop a nuclear strategy that provides de-escalation options through the capability to hold at risk deeply buried targets with minimal, it is hoped, collateral damage, for both the central strategic balance (Russia and China) and regional contingencies (“rogue states” with WMD).

Now there was a time, not long ago, that inclusion of the central strategic balance in all this would have caused consternation. Advocates of low yield earth penetrating nuclear weapons always spoke of them in the context of regional contingencies. Now the B61 and its modifications is a weapon that is NATO, and therefore Russia, centric. For me that is a big change, which we’ve hardly noticed. A lot of my analysis during the Bush era emphasised this because I felt it was an important consideration, but now it’s open and we hardly blink an eye.

The DSB report itself puts tailored nuclear weapons in the Russian context

Russian doctrine is publicly stated as “escalate to de-escalate” based on the assumption that its first use of low yield nuclear weapons against a conventionally superior NATO force would engender a halt to further aggression

This statement is important because, through reasonable mirror imaging, it demonstrates that tailored deterrence is about escalation control through intrawar deterrence.

The interesting thing about the DSB report is that it argues for developing tailored nuclear weapons, both in term of mission and effects, that are new. The B61-12 has an earth penetrating capacity, so that expands its repertoire, but the B61-12 is an LEP warhead so technically speaking not new.

A new low yield earth penetrator would go beyond LEP and would probably be something not too dissimilar to the Robust Nuclear Earth Penetrator, that is a new weapon with a new bomb casing designed for penetrating into the ground and with dial-a-yield options including low yield options.

That’s my hunch. Time will tell whether this hunch is a good one.