Jeffrey Lewis (aka Armscontrolwonk) and Elbridge Colby recently penned a provocative article calling on the Obama administration to modify the B83 gravity bomb in order to hold certain hard and deeply buried targets (HDBTs) in North Korea at risk.
According to Jeffrey and Bridge, this capability would threaten underground bunkers where Kim Jong-Il might seek refuge or hide some of his nuclear forces that cannot be targeted by existing conventional earth penetrators or nuclear weapons, thereby enhancing deterrence and our ability to reassure South Korea. In addition, they argue that such a weapon wouldn’t violate the Nuclear Posture Review’s prohibition on the design and construction of new nuclear weapons with new military capabilities.
The piece has prompted many reactions and in response Jeffrey wrote a follow-up post over at Armscontrolwonk expanding on and clarifying some of their arguments. I think Jeffrey and Bridge highlight a very serious issue (how to deter North Korea), but I disagree with their proposed solution. I laid out my objections in a comment on Armscontrolwonk, which I’m crossposting below the jumb. Be sure to check out the other comments, as well as Jeffrey’s responses, over at his blog here. It’s a fascinating and important debate.
Thanks for the follow up post. A few thoughts:
I don’t really disagree with your point that a modified B83 would not be considered a new weapon under the Nuclear Posture Review – for better or for worse. However, in my view that’s not what this debate should be about.
For me the issue is whether your proposal makes sense for U.S. and South Korean security. I don’t think it does for the following reasons.
First, you write:
“there is some deterrent benefit to being able to hold at risk Kim Jong Il’s leadership facilities and nuclear forces, some of which are likely located in hard and deeply buried facilities immune to conventional attack. Or, to be more precise, I believe deterrence suffers some difficult-to-measure harm from not being able to hold those targets at risk and that steps to remedy that gap may be more reassuring to South Korea than other proposals, such as the deployment of fighter-delivered tactical nuclear weapons that Gary Samore mentioned.”
As you note, this is hardly a ringing endorsement, and still I think it overstates the ability of earth penetrating weapons to hold HDBTs at risk. As others have already pointed out, reliable intelligence about the location of underground targets (and whatever is inside them at a given point in time) is difficult to come by, North Korea could build deeper facilities or shift more assets to mobile facilities, and the collateral damage from an earth penetrating weapon would be extreme, further undermining its credibility. Moreover, an additional earth penetrator would give North Korea a convenient excuse to accelerate its nuclear program, thereby undermining U.S. and South Korean efforts to denuclearize the peninsula. Of course without access to all the relevant classified intelligence information, I can’t rule out that some targets might be susceptible to destruction by a modified B83, but given that North Korea could simply dig deeper in response to the U.S. deployment of such a weapon, I still doubt its’ deterrent benefit.
I also think you could be more precise about what exactly it is you mean to deter. Are you trying to deter North Korea from engaging in limited “peacetime” conventional provocations against the U.S. or U.S. allies, in light of mutual deterrence at the nuclear level (also known as the stability-instability paradox)? Put in another way, are you seeking to enhance deterrence of low-level conventional conflict by denying Kim Jong-Il a nuclear retaliatory capability (and a secure place to hide), such that the U.S. would have less fear of escalating in response to North Korean conventional provocations?
If so, I don’t think a modified B83 would do the heavy lifting you want it to do, for the reasons I’ve already laid out: namely, it can’t effectively hold HDBTs at risk. Furthermore, given Pyongyang’s ability to wreak terrible destruction on Seoul with its conventional forces, I imagine the U.S. would be wary of escalating even if North Korea didn’t have nuclear weapons.
If you’re trying to deter North Korea from launching a large-scale conventional attack against South Korea or threatening to use or using nuclear weapons in a conventional conflict with the U.S. or South Korea (i.e. all-out war), I doubt a modified B83 would add anything to deterrence, as the U.S. already possesses robust nuclear and conventional capabilities with which to eliminate the North Korean regime.
Moreover, I think you also need to consider the implications of a modified B83 for crisis stability. In the event of a severe crisis or once a conventional war has begun, enhanced U.S. counterforce capabilities could prompt North Korea to take destabilizing measures to enhance the survivability of its forces by, for example, predelegating launch authority to field commanders. Likewise, the perceived ability to take out Kim Jong-Il in a hardened underground bunker could also create strong incentives for the U.S. to attack early in a conflict, lest the Dear Leader take steps to increase the survivability of his bunkers and forces, thereby closing the U.S. window of opportunity. While some of these crisis pressures would exist even in the absence of a modified B83, the additional capability would exacerbate them.
Regarding the reassurance of South Korea, I agree that a modified B83 is a better alternative than redeploying U.S. tactical nuclear weapons to the Peninsula. However, that’s the wrong standard by which to judge your proposal, especially since (as far as I can tell) the constituency in South Korea in favor of redeployment is confined to a small number of conservative Korean officials and academics.
I don’t doubt that North Korea’s recent provocations present real security challenges, but I don’t see how the deployment of a small number of modified B83s would be anything more than a temporary means of reassurance – North Korea can simply build deeper bunkers.
In addition, I think there’s a risk to relying on a nuclear capability of highly questionable utility as a measure of the strength and vitality of the U.S. commitment to South Korea’s security. The more the U.S. and South Korea lean on such capabilities as a crutch, the easier it is to avoid difficult but much needed discussions about how the U.S. can continue to guarantee South Korea’s security even as we continue to reduce our reliance on nuclear weapons. I think the extensive discussions among the U.S., South Korea, and Japan that ultimately led to the retirement of the TLAM-N provide an excellent model as to how this can be achieved.
I also weigh the balance of nonproliferation and deterrence goals differently than you do. Regardless of an existing mid-1990s era requirement for a hard rock penetrator, a modified B83 (particularly to deter limited conventional attacks) would signal a step back in the U.S. effort to reduce its reliance on nuclear weapons, thereby undermining U.S. nonproliferation objectives. I think this cost (along with the others I’ve highlighted above) outweighs the very minimal (at best) deterrence benefit a modified B83 might provide.
Finally, given the current economic environment, I think you need to at least offer an estimated cost of the modification you’re proposing. Given that you don’t envision this as anything more than a niche capability, perhaps the cost would be minimal, but it would be helpful in assessing its affordability and opportunity costs.