rational defense

No nuclear weapons were tested in 1997 — only the second year since mankind detonated its first atomic bomb in 1945 that no testing took place. The 1990s saw what has proven to be — in effect — the end of Cold War-era nuclear testing. In 1998, of course, India and Pakistan both carried out a series of nuclear tests. But since that year, there has been only a single nuclear detonation: North Korea’s in 2006 (and the seismographic data from that test was not indicative of even a rudimentary nuclear device).

This has profound implications for the future of the world’s existing nuclear arsenals.

What has now become the U.S. National Nuclear Security Administration (founded in 2000) has argued, along with the current administration, that the current Stockpile Stewardship and Life Extension Programs are not sufficient for the long-term maintenance of the American nuclear arsenal, and that there is a mounting need for what has been dubbed the Reliable Replacement Warhead (RRW). While there remains a need for a clear, concise and compelling articulation of the role of nuclear weapons in the 21st century, there are very real constraints in play.

The concept of RRW is not about designing a new weapon tailored for the 21st century, but rather making carefully calculated tweaks to existing warhead designs in order to enhance reliability and maintainability and maximize sustainability and safety considerations.

The modern two-stage thermonuclear warheads currently in the arsenal are extraordinarily complex things. They are the product of literally hundreds of nuclear tests — both full-scale tests and even more subcritical experimentation (including hydronuclear and hydrodynamic techniques) — and are thought to contain non-spherical primaries, a particularly complicated design. These warheads were designed in the last days of the Cold War, and were designed to maximize accuracy and what is know as yield-to-weight ratio — maximizing the destructive power per pound, an important consideration for weapons to be mounted on intercontinental ballistic missiles (ICBMs). At that point, these warheads were configured for use in multiple independently targetable reentry vehicles, with multiple warheads mounted on a single ICBM.[1]

The U.S. nuclear weapons enterprise uses some of the world’s most powerful supercomputers to run simulations and model the impact of age and time on the current arsenal. But ultimately, these Cold War-era warheads were designed in a paradigm of regular testing and ongoing weapons development. New weapons were expected to eventually replace them so indefinite shelf life was not a design consideration.

The Stockpile Stewardship and Life Extension Programs have stretched these designs, and there is no doubt that the current arsenal remains credible. This confidence is one of the most important considerations for a country’s nuclear arsenal. The nuclear weapons a country fields must be reliable and proven in order for both the government itself and other countries alike to have a high degree of confidence in the credibility of the deterrent itself.

But while the Stockpile Stewardship and Life Extension Programs have certainly achieved this objective (and could likely continue to do so for years to come), a degree of uncertainty and prudence has required the maintenance of two warhead types for each delivery system so that, in the event that one design is found to have an irreparable problem, it can be replaced without affecting the status of the American deterrent. This has resulted in many more warheads being kept in a reserve status than would otherwise be the case.

The question about how America prepares to sustain a nuclear arsenal for the foreseeable future — i.e. indefinitely — is reaching a critical juncture. The engineers that have first-hand experience with nuclear weapons design and testing are approaching retirement age. Their personal and intimate knowledge about the smallest and subtlest design choices made in the current weapons architecture will soon test the institutional knowledge of their labs, and something will almost certainly be lost.

As attractive as it might be to think about scaled-down warhead designs or articulating a mission before the design process might begin, the reality is that the ultimate goal has already been articulated: a sustainable deterrent without further nuclear testing. The implication of that goal is a decisive constraint that defines the weapon to be built. It is, simply, the very weapons with which the current engineer pool — both the elder engineers that actually designed the warheads and the next generation that has come up learning the finer points of sustaining them — has the most intimate experience, and more pointedly the experience of working to sustain and extend service life. These are the most modern warheads in the arsenal and are equipped with the most advanced safety features.

This underlying design is the inescapable choice for a country that intends to sustain its arsenal indefinitely without testing. And if that is the goal, the way to maximize the chances for success without testing is to allow the nuclear weapons labs to design and build new warheads now based on the articulated objectives of the RRW program.

While total disarmament is a nice conversation to have, the geopolitical reality is that there remains a deep uncertainty about the future threat environment, and while reductions in the nuclear arsenal are absolutely in the cards, so long as America intends to forgo testing, the warheads of that arsenal are necessarily constrained to only modest and conservative tweaks to the designs of the warheads currently in the arsenal.

Ultimately, there are almost certainly — even necessarily — limits to what the Stockpile Stewardship and Life Extension Programs can accomplish because of the considerations that informed the original design of the warheads currently deployed. The finer points of this are obviously both classified and best left to the engineers themselves. But these underlying considerations make RRW (or a similar program under a different name) the path most likely to maximize the long-term sustainability of the arsenal and minimize the chances of further testing. But the problem with RRW, aside from the public distaste for it, is that the question has already been delayed for years and the way to both set up RRW to succeed and to maximize the chances for its success is to push forward as soon as possible.

The Stockpile Stewardship and Life Extension Programs can probably continue to do the trick for a decade or more. But at some point, a new design will likely become necessary. The further down the road that this point is reached, the more familiarity with the existing designs and the more first-hand experience with actual weapons design will have been lost.

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1 The exception to this is the cancelled MGM-134 “Midgetman” light ICBM, which was to be armed with a single Mk-21 reentry vehicle — the same multiple independently targetable reentry vehicle mounted in sets of eight to ten on the LGM-118A Peacekeeper heavy ICBM.