An Insider’s View of Nuclear Weapons Modernization

October 2016

By Don Cook

Although the U.S. nuclear weapons stockpile is safe and secure today, technological advances from the research and development portion of the Stockpile Stewardship Program have shown that improvements in safety and security can be achieved by incorporating more advanced technologies than those available during weapons manufacturing in the 1970s and 1980s. 

The necessity to ensure reliability as systems age is clear. Automobiles with a comparable average age as the weapons in the stockpile (29 years) have lower reliability today than when they were produced, if they are even still on the road. Rubber and plastic degrade and become brittle, metal corrodes, and connections that were once tight become loose. In undertaking weapons life extension programs (LEPs), often referenced as weapons modernization,1 the emphasis is on returning the weapons to their original level of reliability, which, although classified, was very high. 

The last B53 thermonuclear bomb was dismantled at the Pantex plant near Amarillo, Texas, in 2011. The nine-megaton weapon, 600 times the explosive power of the atomic bomb dropped on Hiroshima, Japan, was carried aboard U.S. Air Force B-52 bombers on alert during the 1960s and remained in active service until 1997. (Photo credit: National Nuclear Security Administration)When nuclear testing ended in 1992, the United States had recently completed production of many new nuclear weapons during the Reagan modernization of the 1980s. The warheads that remain in the current stockpile were young, with an average age of six years. Today, however, the United States has the oldest stockpile it has ever had and the smallest stockpile since the Eisenhower administration, reduced by more than 85 percent from the Cold War peak. The intent of the LEPs is not to introduce new weapons; the programs are focused on extending the life of current U.S. nuclear weapons while improving safety and security and maintaining reliability. 

Formulation of the LEP strategy was guided by the Nuclear Posture Review (NPR), the Congressionally-mandated comprehensive review of U.S. nuclear deterrence policy, strategy, and force posture for the next five to 10 years. The 2010 NPR Report said, “By pursuing a sound Stockpile Management Program for extending the life of U.S. nuclear weapons, we can ensure a safe, secure, and effective deterrent without the development of new nuclear warheads or further nuclear testing.” Further, it states, LEPs “will only use nuclear components based on previously tested designs, and will not support new military missions or provide for new military capabilities.”2

Intensive study from 2011 to 2014 by the government’s Nuclear Weapons Council and its constituent elements representing the military commands, elements of the Department of Defense, and the National Nuclear Security Administration (NNSA) resulted in broad agreement on a national strategy for comprehensive extension of the life of U.S. nuclear warheads. This is labeled the “3+2 strategy.”3

In accordance with the NPR and the New Strategic Arms Reduction Treaty (New START) with Russia, the United States will consolidate the number of nuclear weapon types and reduce the overall size of its stockpile. The 3+2 strategy lays out a path for reducing the number of nuclear weapon types from 12 to five. Of the five types, two will be air-delivered weapons (one bomb type and one cruise missile type), and three will be interoperable warheads that can be deployed on intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs). This strategy will take 30-plus years to implement fully. 

Implementing the Strategy

The first implementation element of the 3+2 strategy is the B61-12 LEP. The B61-12, now in its fifth year of full-scale engineering development, will consolidate four variants of the B-61 bomb and will improve the safety and security of the oldest weapons system in the U.S. nuclear arsenal. The LEP is centered on the strategic bomb capability, balancing greater accuracy provided by a modern tail kit with a substantial reduction in yield, with no overall change in military requirements or characteristics. The NNSA is accountable for the nuclear ordnance (the bomb body) while the Air Force is accountable for the integrated tail kit.

The B61-12 was recently approved to move into the production engineering phase and is currently planned for a first production unit in fiscal year 2020, consistent with the conclusion of the LEP for the W76-1 SLBM warhead at the Pantex assembly plant in Texas in fiscal year 2019. The B61 remains a key element of the air-delivered leg of the U.S. nuclear deterrent and is a key weapons system in the extended nuclear deterrent covering U.S. allies. Once the B61-12 LEP is completed over roughly a four-year period and confidence is gained with B61-12 weapons in service, the B83—the last megaton-class weapon in the arsenal—will be retired. The result is (1) a reduction of the number of bombs by a factor of two, (2) the removal of a megaton-class weapons system, (3) a reduction in enriched uranium and plutonium of more than 80 percent in the bomb portion of the air leg, and (4) a reduction in overall destructive power by the same amount (80 percent).

The 3+2 strategy calls for a replacement of the current air-launched cruise missile (ALCM). The Nuclear Weapons Council has narrowed options under consideration for the nuclear package. Given the investment in development of modern non-nuclear components for the B61-12 LEP, it makes economic sense to reuse and reapply as much of that component set as possible to the ALCM replacement. Current schedules within the nuclear security enterprise would allow movement of a life-extended cruise missile warhead to follow the B61-12 in manufacturing and assembly at Pantex, with a first production unit in the fiscal year 2025-2027 time frame. 

Consolidation of the four present ballistic systems into three interoperable systems will enable an eventual reduction in the number of weapons retained as a hedge against technical failure. In today’s stockpile, if the United States experiences a technical problem in a bomb, cruise missile warhead, or ballistic missile warhead type, there can be a period of time when one of two elements in one leg of the deterrent triad is “out of commission” while the problem is solved. In the future, with two or three types of warheads available for insertion into ICBM or SLBM aeroshells, intraleg technical hedging will be possible. This capability has been shown to remove the need for a significant part of the technical hedge, but only when fully implemented.

The NPR Report recommended initiating a “study of LEP options for the W-78 ICBM warhead, including the possibility of using the resulting warhead also on SLBMs to reduce the number of warhead types.”4 In 2011 a concept study was initiated, focusing on the use of common components, adaptable architectures, and interoperability between ICBM and SLBM platforms.

A budgetary decision made in 2014, supported by a technical assessment from the stockpile surveillance program, deferred further work on the interoperable weapons for five years. In the interim, increased emphasis was given to a new arming, fusing, and firing unit for the W88 warhead. That effort was already in full-scale engineering development in 2014 and was expanded to include replacement of the conventional high explosive component in order to extend the weapon’s lifetime by an additional 10 to 15 years. The W88 Alt 370 will form the basis of the arming, fusing, and firing unit for the current W88 and W87 systems and for the first interoperable warhead, currently designated as the W78/88-1. 

The issue of conventional high explosives (CHE) versus insensitive high explosives (IHE) in nuclear weapons is a factor in life extension efforts. The latter type are powerful explosives that have improved safety characteristics because they are remarkably insensitive to high temperatures, shock, and impact. It has been an objective to move from CHE to IHE in the course of weapons life extensions. All of the air leg is already based on IHE, but progress remains to be made in ballistic systems. Why is this important? Fundamentally, there is no single greater improvement in weapons safety than moving to IHE. Because the energy content per unit of mass of IHE is just 70 percent that of CHE, however, the IHE takes up more space, and IHE-based weapons must have lower yields than CHE-based weapons in order to fit into existing aeroshells. U.S. Strategic Command and the other entities within the Nuclear Weapons Council made the decision at the outset of the work on interoperable weapons to accept a reduction in weapons yield in order to get the safety advantage. 

Recent Actions to Reduce Nuclear Weapons Yield

Reduction of nuclear weapons yield, made possible by improvements in accuracy or method of delivery, has been a decades-long trend for nuclear weapons planners. Although several reductions have been made in the context of arms control agreements, some have been made unilaterally by the United States in the context of changing security considerations. All of these final actions occurred during the Obama administration.

• The decision to remove multiple independently targetable re-entry vehicles (MIRVs) from the Minuteman III missiles was made in 2010. This action reduced the number of weapons on each missile, within a fixed set of missiles, by up to a factor of three. More recently, the decision on force structure reduced the number of armed Minuteman III missiles from 450 to 400.

• The last W62 warhead unit was dismantled at the Pantex plant in 2010. When the decision to retire the MX missile was made in 2004, the W62 warheads mounted on the Minuteman III missile were replaced by fewer W87 warheads, which had been mounted on the MX, reducing the explosive power carried on each missile. This was seen as a step forward in safety because the W87 uses insensitive high explosives, whereas the W62 used the more volatile conventional high explosives.

• The last B53 unit was dismantled at Pantex in 2011. The replacement of the B53 gravity bomb by the B61-11 earth penetrator bomb in 1998 removed a now unclassified nine-megaton weapon and replaced it with a much smaller yield weapon, which allowed similar targets to be held at risk because of its earth-penetrating capability.

• The last W80-0 unit was dismantled at Pantex in 2013, removing an entire weapons system and not replacing it with anything else.

Weapons Numbers

Reductions in deployed nuclear weapons and delivery platforms are being made bilaterally under the New START. Two significant decisions made in presidential approval of the NPR were the retirement of the W80-0 warheads for submarine-launched cruise missiles (SLCM) and the de-MIRVing of the ICBM fleet, that is, eliminating multiple independently targetable re-entry vehicles from each missile. These decisions reduced the number of weapons in the U.S. arsenal and the overall destructive power of the U.S. deterrent by a substantial amount.

One argument advanced against the current LEP plan is that the number of weapons of a specific type should be reduced first, then the remaining weapons should be life extended. In theory, this would work, but it does not work in practice. The reason is that there is insufficient reliability in weapons as they age, and a larger number of “technical hedge” weapons must be retained, just for having the parts to cannibalize to rebuild other weapons. An example is that, in 2000, just 12 years after the W88 weapons system (the most modern one) had entered service, more than 90 percent of the parts were no longer available. For that reason, weapons programs execute a “life of program” procurement, typically sufficient to supply parts from the strategic reserve for up to 25 years. Now, the average age of weapons is 29 years, and replacement parts are not available.

It is only once that an LEP has been completed and field implementation has demonstrated reliability in service, typically two to four years, that there is sufficient confidence to permit retirement and disassembly of the units that the life-extended ones replace. In other words, reduction in weapons numbers comes as a direct result of the LEPs, not instead of them. 

In addition, as the engineering design and production phases of the LEPs progress, the number of weapons that actually go through the process is reduced substantially. Although this depends most heavily on military planning requirements and arms control agreements, the record is clear: By the time the W76-1 LEP is completed at the end of 2019, the number of W76 units in the stockpile, although classified, will have been reduced by a substantial amount. Because the yield of the units was not changed, the overall system yield (that is, the total yield of all weapons of that type) will have been reduced by the same amount. Furthermore, by the time the B61-12 LEP is completed, near the end of 2025, fewer than half of the number of B61 gravity bombs will be in the stockpile. That alone would reduce the overall system yield by half. Yet, because the B61-12 delivery accuracy will be better than that of the current systems, the yield of the B61-12 units will be reduced, preserving the military effectiveness but reducing the amount of special nuclear material needed to produce the required yield. 

Also, as confidence in the B61-12 system was increased in the early phases of the LEP, the decision was made that the earlier planned LEP for the B83 weapon was not needed and that system would be retired as life-extended B61 units entered service and proved their reliability in service deployment. That decision will remove the last of the “megaton-class” weapons in the U.S. arsenal. Collectively, these decisions reduce the amount of special nuclear material in the bomb leg of the deterrent by more than 80 percent, and the overall destructive power of the bomb leg will be reduced by the same amount. Counting numbers of weapons alone is inadequate to depict the reduction in the overall destructive power of the U.S. stockpile.

Sandia Labs mechanical engineer Ryan Schultz adjusts a microphone for an acoustic test on a B61-12 bomb system on October 30, 2014. The unit is surrounded by banks of speakers that expose it to sound pressure at 131 decibels, similar to a jet engine. (Photo credit: Randy Montoya/Sandia Labs)

Numbers Versus Yield

The arms control community understandably has been focused on the reduction in weapons numbers, but less attention has been paid to the associated reduction in weapons yield, or overall destructive power of the stockpile. This has become an issue of debate, particularly over concerns expressed by some in the arms control community that lower yields, coupled with advances in delivery systems improving precision, speed, and stealth, would have the undesired effect of making nuclear weapons more “usable”5 and, further, that if a weapon is more useable, it is more likely to be used. Yet, I believe, a lower-yield, more accurate U.S. weapon constitutes a better deterrent specifically because it will be regarded by an adversary as more usable and that the likelihood of weapons use is, therefore, lower, not higher. This has certainly been a hotly debated issue for the B61-12 LEP.6 

Given the facts that following the W76-1 and B61-12 LEPs, the number of warheads of each type will have been reduced by more than a factor of two and that the B61-12 LEP will have enabled the B83 retirement and reduced the overall destructive power of the air leg by 80 percent, why has the arms control community not been encouraged by the programs? Why focus only on the numbers, rather than the numbers and the yield? The Obama administration and the president have received insufficient credit by the arms control community for the important decisions made. 

Moreover, why is the arms control community not taking credit for having urged the administration to go in this direction? My experience is that points made by the arms control community have usually been good ones and ones to which I paid attention. It has been argued that President Barack Obama has reduced the stockpile by smaller amounts than prior, Republican presidents. Yet, it is always easier for a Republican president to make arms reductions because the Democrats will cross party lines to support that. 

Another fact, articulated in the 2010 NPR Report completed by the Obama administration, is the de-MIRVing of the ICBM fleet. That single decision reduced the yield of the sum of the weapons carried by each of the 450 missiles (400 after New START force structure implementation) by a factor of up to three. That reduction is to be completed by February 2018.

In the aggregate, the total destructive power of the U.S. arsenal is shrinking faster than simply the number of nuclear weapons. It is important that the arms control community understand this and discuss the details. The arms control community can be most helpful in taking the next steps in arms control with regard to nuclear weapons in three areas.

1. Pay attention to weapons yields along with numbers of weapons, and advocate a reduction in yields and a reduction in the overall destructive power of the stockpiles of the United States, Russia, and China rather than advocating against lower weapons yields.

2. Recognize and support the U.S. direction of “getting out of the megaton business” and advocate that Russia and China take similar steps.

3. Advocate an extension of the New START that includes all nuclear weapons, both strategic and nonstrategic, and that permits Russia and the United States to make their own decisions on the relative balance between the two types, within the same fixed ceiling on weapons numbers.

A continuing emphasis on weapon dismantlements and component disassemblies is needed. During the Obama administration, more than 2,000 nuclear weapons have been dismantled, and Congress approved the president’s fiscal 2016 budget request to accelerate the dismantlement rate by 20 percent. As the arms control community knows, weapons plans always can change but disassemblies are irreversible.


1.   Kingston Rief, “U.S. Nuclear Modernization Programs,” Arms Control Association, September 2016,

2.   U.S. Department of Defense, “Nuclear Posture Review Report,” April 2010, pp. 7, 39, (hereinafter NPR Report).

3.   National Nuclear Security Administration, “Fiscal Year 2016 Stockpile Stewardship and Management Plan,” March 2015, pp. 1-7, 1-8, 3_16_2015_reducedsize.pdf.

4.   NPR Report, p. 39.

5.   William J. Broad and David E. Sanger, “As U.S. Modernizes Nuclear Weapons, ‘Smaller’ Leaves Some Uneasy,” The New York Times, January 11, 2016.

6.   Hans Kristensen, “The B61 Life-Extension Program: Increasing NATO Nuclear Capability and Precision Low-Yield Strikes,” Federation of American Scientists, June 2011,

Don Cook served in the Obama administration as deputy administrator for defense programs at the National Nuclear Security Administration from June 2010 through July 2015. He was managing director and CEO of the Atomic Weapons Establishment in the United Kingdom from 2006 through 2009 following work at Sandia National Laboratories from 1977 through 2005.