How Many Nukes Make Deterrence Credible?

Military and political leaders frequently emphasize the need for the United States to maintain a credible deterrent. While I have never seen them define that term*, there has always been an implicit assertion that a much smaller nuclear arsenal would not be a credible deterrent. As with my approach to the risk posed by nuclear weapons, it is wise to delve beneath vague platitudes and ask for hard numbers, in this case: “How many nuclear weapons are needed to make deterrence credible?”

Is it the 5,113 in our current arsenal (plus several thousand more that are admitted to be awaiting dismantlement)? Is it the 31,255 that we had at the peak of the arms race? Or some other number?

An OpEd in today’s New York Times whose authors are at the Air War College and the USAF School of Advanced Air and Space Studies puts the number at several hundred, shining a spotlight on the bloated nature of our current arsenal. That number came as no surprise since a statement that has been on my web site for over two years says in part:

Russia and the United States each have thousands of nuclear weapons, whereas a few hundred would more than deter any rational actor and no number will deter an irrational one. Either side could therefore reduce its nuclear arsenal with little to no loss in national security, even if the other side did not immediately reciprocate. In light of the growing specter of nuclear terrorism, a reduced nuclear arsenal could even enhance national security by lessening the chance for theft or illicit sale of a weapon.

Of the seven prestigious signers of that statement, two have notable national security backgrounds: Adm. Bobby R. Inman, was Director of the National Security Agency and Deputy Director of the CIA as well as a nominee for Secretary of Defense, while Dr. Richard Garwin is recognized as one of the top few contributors to the first thermonuclear weapon or H-bomb.

The last sentence of the above excerpt refers to the fact that keeping track of thousands of nuclear weapons is an almost impossible task, as evidenced by our Air Force misplacing six warheads back in 2007. A B-52 was supposed to fly from Minot AFB in North Dakota to Barksdale AFB in Louisiana with 12 cruise missiles under its wings, all with dummy warheads. By mistake, only 6 dummies were used, with 6 real warheads on the remaining missiles. For over a day, those warheads were improperly guarded and vulnerable to theft.

An even more basic question that needs to be asked is whether any number of nuclear weapons constitutes a credible deterrent. How credible is a threat to destroy the world, ourselves included?

Martin Hellman
Member, National Academy of Engineering
Professor Emeritus of Electrical Engineering, Stanford University

* Interestingly, the only time I have seen this question raised was in 2006, when the US asked India to define its minimum credible deterrent. That seems to be a question that we should be asking ourselves as well. If anyone is aware of other times that a definition was sought, please add it as a comment below so I can add it to my knowledge data base.