Chapter
4

Nuclear Weapons

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Overview

To maintain a safe, secure, and effective U.S. nuclear stockpile, DoD works with the National Nuclear Security Administration (NNSA), through the Nuclear Weapons Council (NWC), to maintain the quantity and quality of weapons necessary for U.S. national security, as determined by policy and presidential direction. In the post–Cold War era, the United States terminated its production of new weapons and stopped underground nuclear explosive testing. As a result, the NNSA today maintains the stockpile through the application of science, technology, engineering, high-speed computing, and manufacturing efforts within its Stockpile Stewardship Program. The United States, however, is entering into an era of both nuclear delivery system and nuclear weapons modernization. The Departments will partner in these modernization activities and must align their efforts in a way that has not been achieved in many decades.

Nuclear Weapons Stockpile

All nuclear weapons in the U.S. stockpile are designated as either a warhead (W) or a bomb (B).1 Weapons that have different engineering requirements because they must interface with a launch platform or delivery vehicle are called warheads. Weapons that do not have these interface requirements, such as gravity bombs and retired atomic demolition munitions (ADM), are called bombs. Using these definitions, the total number of U.S. nuclear weapons equals the sum of warheads plus bombs. In this handbook, the term “warhead” is used to mean both warheads and bombs, and the terms “weapon” and “warhead” are used interchangeably. The term “warhead-type” is used to denote a population of weapons with the same design. Weapons in the current force structure include B61, W76, W78, W80, B83, W87, and W88.

Comprehensive List of Warhead-Types and Descriptions

Comprehensive List of Warhead-Types and Descriptions

Throughout the history of nuclear weapons development, the United States has produced families of warheads based on a single-warhead design. Thus, some weapons in the stockpile were developed as modifications (Mods) to an existing design. For example, the B61 bomb has had 12 variations over time. Each variation was designated as a different Mod. Each Mod used the basic design of the B61, but incorporated different components that changed the operational characteristics of the weapon in a significant way. Four of these Mods are still in the current stockpile: B61-3, B61-4, B61-7, and B61-11. The B61-12, which will replace all current variants of the B61, is currently in production. This is an efficient approach when conducting quality assurance testing and evaluation because warhead Mods that have common components can be tested and maintained as a family of warheads.

All nuclear weapons in the stockpile are designated as strategic or non-strategic. Strategic weapons are those delivered by intercontinental ballistic missiles (ICBM), submarine-launched ballistic missiles (SLBM), or heavy bombers. All other nuclear weapons are considered non-strategic. Non-strategic nuclear weapons, which are sometimes called “tactical” or “theater” nuclear weapons, have historically included bombs delivered by dual-capable aircraft (DCA), which can be used for both nuclear and conventional missions; warheads in cruise missiles delivered by nonstrategic aircraft; warheads on sea-launched cruise missiles (SLCM); warheads on ground-launched cruise missiles (GLCM); warheads on ground-launched ballistic missiles (GLBM) with a maximum range that does not exceed 5,500 kilometers, including air-defense missiles; warheads fired from cannon artillery; ADMs; and anti-submarine warfare nuclear depth bombs. Today, only air-launched cruise missiles (ALCMs) and gravity bombs delivered by DCA are in the non-strategic category. Future planning calls for sea-launched nuclear cruise missiles to once again be introduced into the stockpile.

Figure 4.1 illustrates U.S. nuclear weapons and associated delivery systems, both current and future. All U.S. nuclear weapons in the current stockpile were designed and produced in the 1970s and 1980s, with an original design life of 20 years. Since the end of U.S. nuclear production in 1991, the United States has developed and executed life extension programs (LEPs) for weapon-types in the legacy Cold War stockpile. For example, the W76 entered the stockpile in 1978 and the first life-extended warhead re-entered the stockpile in 2008. LEPs address only non-nuclear components and do not replace nuclear components. Non-nuclear component categories include explosive materials, arming devices, fuzing devices, casings, detonators, firing devices, safing devices, security devices, neutron generators, power sources, interface systems, and electronics. Eventually, all nuclear weapons in the stockpile will need to be replaced using newly manufactured nuclear components. Currently, the United States cannot produce these new components. There is some debate surrounding how long nuclear components will continue to perform as required.

Figure 4.1
Figure 4.1 U.S. Nuclear Weapons and Associated Delivery Systems

For example, the W76 entered the stockpile in 1978 and the first life-extended warhead re-entered the stockpile in 2008. LEPs address only non-nuclear components and do not replace nuclear components. Non-nuclear component categories include explosive materials, arming devices, fuzing devices, casings, detonators, firing devices, safing devices, security devices, neutron generators, power sources, interface systems, and electronics. Eventually, all nuclear weapons in the stockpile will need to be replaced using newly manufactured nuclear components. Currently, the United States cannot produce these new components. There is some debate surrounding how long nuclear components will continue to perform as required. Figure 4.2 delineates the ages of the weapons in the current stockpile.

Warhead
Type
Date of
Entry into
Stockpile
Planned
LEP1
First Prod.
LEP
Planned
Repl.2
Projected
FPU5 for
Replacement
Nuclear
Component
Age at Initial
Replacement6
B61-3/4* 1979 B61-12 LEP 2020 FAW3 ~2040–2050 ~60–70 yrs
B61-7/11** 1985/1997 B61-12 LEP 2020 FAW ~2040–2050 ~60–70 yrs
B83-1** 1983 Retired by 2025 n/a n/a n/a n/a
Cruise Missile
W80-1
1982 W80-4 LEP 2025 FAW ~2040–2055 ~60–75 yrs
SLBM W76 1978 W76-1 LEP 2008 FBW4 ~2045–2047 ~65–70 yrs
ICBM W78 1979 n/a n/a W87-1 ~2030 ~50 yrs
ICBM W87 1986 Partial LEP 1999 FBW ~2035–2040 ~50–55 yrs
SLBM W88 1989 Alt 370
Refresh
2022 FBW ~2035–2040 ~45–50 yrs
* Non-strategic bomb ** Strategic Bomb   1 Life extension programs (LEP) reuse nuclear components   2 Replacement requires nuclear component   production   3 Future Air-Delivered Warhead (FAW) timeframe identified; characteristics to be determined   4 Future Ballistic Missile Warheads (FBW) initial studies planned; diversity and characteristics to be determined   5 First Production Unit   6 Replacement dates are notional
Figure 4.2 Aging of the Legacy Stockpile

Figure 4.3 correlates delivery platforms and vehicles to current and near-future weapons in the U.S. stockpile.

Delivery Platform Delivery Vehicle Current Weapon(s) Near-Future Weapon(s)
SSBN SLBM W76-0
W76-1
W76-2
W88
W76-1
W76-2
W88
ICBM (Platform/Vehicle) W78
W87-0
W87-0
W87-1
DCA Gravity Bombs B61-3/4 B61-12
Bombers B61-7/11
B83
B61-12
DCA or Bomber ALCM W80-1 W80-4
TBD SLCM   TBD
Figure 4.3 Current and Near-Future Nuclear Delivery Systems and Associated Weapons

Stockpile Quantities

While the United States has continued to reduce the number and salience of nuclear weapons, other nations, including Russia and China, have moved in the opposite direction. They have added new types of nuclear capabilities to their arsenals and increased the role of nuclear forces in their strategies and plans.

Figure 4.4
Figure 4.4 U.S. Warhead Production from the 1940s through the 2020s
(There have been no new warhead-types produced since the 1980s.)

Stockpile quantities are authorized annually by presidential directive that specifies quantities of warheads, by type and by year, for a multi-year period. Figure 4.4 illustrates U.S. warhead production from the 1940s through the 2020s.

The United States has led the world in decreasing nuclear weapons quantities consistent with U.S. national security objectives. As of September 2017, the stockpile consisted of 3,822 warheads. Figure 4.5 shows stockpile quantities between 1962 and 2017. Since 2018 the U.S. government has not declassified stockpile quantities. Classification in future years will be decided on a case-bycase basis.

Figure 4.5
Figure 4.5 Stockpile Numbers End of Fiscal Years 1962–2017
(does not include weapons retired and awaiting dismantlement)

Nuclear Weapons Stockpile Hedge

The stockpile is subject to many uncertainties and associated risks. These include the possibility of an unforeseen catastrophic failure of a class of delivery platform/vehicle, warhead-type/family, an unexpected change in the geopolitical situation, or advances in adversary capabilities and defenses, which could require an increase in the number of weapons available for use. It is vital for DoD and NNSA to have procedures in place to mitigate these and other risks with a strategy that accounts for threats to the stability of the nuclear deterrent at lower stockpile levels.

Basic approaches to stockpile risk mitigation include: the existence of a significant warhead production capability, which existed prior to 1991; maintenance of warheads designated to counter significant unforeseen events, which have been maintained since 1991; or some combination of the two, which is the plan as the United States transitions to limited nuclear weapon production over time. Maintaining warheads to counter unforeseen events is referred to as a “hedge.” During the Cold War, the United States maintained a robust production capability to augment stockpile quantities as required. Today, the United States does not have an active, effective nuclear weapons production capability and relies on maintaining warheads as a hedge to reduce risks.

In the absence of a modernized nuclear infrastructure and the reestablishment of a fissile component production capability with sufficient capacity, the decision to reduce the quantity of warheads designated to mitigate unforeseen events and to dismantle additional weapons is not taken lightly. Hedging strategies and the size and composition of the warhead hedge are complex issues that are considered by policy and military decision makers at the highest levels.

Stockpile Configuration

The current stockpile is composed of weapons developed and produced during the Cold War and maintained well beyond their original planned lives for roles and missions that have evolved significantly since their original production. Modern stockpile configuration involves maintaining aging weapons in an environment where they cannot be replaced once dismantled or they become irreparable. Stockpile composition refers not only to the differences among bombs and warheads or strategic and non-strategic weapons, but also to the various stockpile categories into which the weapons are divided. This enables the United States to maintain the required numbers of deployed weapons together with those that could be deployed if they were ever needed.2

It is necessary for the government to identify the numbers, types, and configurations of nuclear warheads required to support an array of employment options and address possible contingencies. The United States must maintain the required number of operationally ready weapons to ensure confidence in the credibility of the nuclear deterrent, maintain strategic stability with Russia and China, and assure U.S. allies of the credibility of the U.S. nuclear umbrella. Because some contingencies are based on strategic warning, meaning the United States would know in advance of the need to employ its nuclear weapons to respond to emerging circumstances, not all nuclear weapons must be maintained in an operationally responsive mode. To save resources and preserve limited facilities and capabilities, some weapons are maintained in less-ready modes, requiring maintenance action or component replacement or production to become operationally ready.

Because all U.S. nuclear weapons are not ready for immediate use all of the time, balancing the various operational requirements against physical, logistical, and fiscal realities is challenging. Considering the United States has no current capability to mass produce fissile components for nuclear weapons, stockpile composition must retain some flexibility to allow for options in the event of a technological failure or to augment U.S. nuclear forces in response to geopolitical reversals. Stockpile composition is a function of configuration management (the categorization of warheads by function and readiness state) and the associated logistical planning.

Configuration management requires warheads in different status to be designated in different categories. For example, operational warheads are called the active stockpile. An operational weapon is maintained with functioning limited life components (LLCs), such as power sources (batteries) and tritium gas bottles, in place. Nonoperational warheads are called the inactive stockpile and do not maintain LLCs. Based on employment plans, strategic requirements, and logistical requirements, the NWSP specifies the number of warheads required to be operational in a given year.

Active Stockpile

Active stockpile warheads are maintained in an operational status and undergo regular replacement of LLCs (e.g., tritium components, neutron generators, and power-source batteries), usually at intervals of a few years. Active stockpile warheads are also refurbished with all required life extension program (LEP) upgrades, evaluated for reliability estimates, usually every six months, and validated for safety, usually every year. These warheads may be stored at a depot, operational base, or uploaded on a delivery vehicle (e.g., a reentry body (Navy) on an SLBM, a reentry vehicle (Air Force) on an ICBM, an air-launched cruise missile, or a delivery aircraft).

Active stockpile warheads include: active ready (AR) warheads that are operational and ready for wartime employment; active hedge warheads that serve as part of the technical or geopolitical hedge and can serve as active ready warheads within prescribed activation timelines; and active logistics warheads to facilitate workflow and sustain operational status.

Inactive Stockpile

Inactive stockpile warheads are maintained in a nonoperational status. Inactive stockpile warheads have their tritium components removed as soon as logistically practical, and the tritium is returned to the national repository.3 Other LLCs are not replaced until the warheads are reactivated and moved from the inactive to the active stockpile. Some inactive stockpile warheads are refurbished with all required LEP upgrades, while others are not upgraded until the refurbishment is required for reactivation. Some inactive stockpile warheads are evaluated for reliability estimates, while others may not require this. All inactive stockpile warheads are validated for safety, usually every year, and are normally stored at a depot rather than an operational base.

Inactive stockpile warheads include: inactive hedge warheads that are a part of the technical or geopolitical hedge and can serve as active ready warheads within prescribed activation timelines; inactive logistics warheads that serve logistical and surveillance4 purposes; and inactive reserve warheads retained as a long-term response to risk mitigation for technical failures in the stockpile.

Warhead Readiness States
Figure 4.6
Figure 4.6 Warhead Readiness States

A warhead readiness state (RS) refers to the configuration of the weapons in the active and inactive stockpiles. Figure 4.6 depicts the readiness states and categorizes them as part of the active or inactive stockpile. Because not all weapons are maintained in an AR configuration, there are lead times associated with reactivating weapons not in the active stockpile or designated as augmentation warheads.5 However, the RS of any particular warhead should be transparent to the force provider (DoD) insofar as NNSA is able to meet requirements for maintenance and reactivation on schedules previously agreed to by both Departments. The RS is determined by stockpile category, location, and maintenance requirements. Currently there are six different readiness states, divided into active and inactive stockpiles, defined below.

Active Stockpile. Strategic and non-strategic warheads maintained to ensure Combatant Command (CCMD) requirements for operational warheads are met and are updated to incorporate the latest warhead refurbishment-Mods or alterations (Alts). CCMD orders specify the allocation of operational warheads and readiness timelines. Operational warheads are fully assembled warheads with a tritium gas transfer system and other LLCs installed.

  • Active Ready (RS 1) – Warheads designated available for wartime employment planning. AR warheads are loaded onto missiles or available for generation on aircraft within required timelines.
  • Active Hedge (RS 2) – Warheads retained for deployment to manage technological risks in the AR stockpile or to augment the AR stockpile in response to geopolitical developments. These warheads are not loaded onto missiles or aircraft. Warheads are available to deploy or upload per prescribed U.S. Strategic Command (USSTRATCOM) activation timelines.
  • Active Logistics (RS 3) – Warheads used to facilitate workflow and sustain the operational status of AR or Active Hedge quantities. These warheads may be in various stages of assembly in preparation for deployment. However, gas transfer systems are installed or co-located on the operational base in sufficient quantities to meet the readiness timelines specified in CCMD operational orders. Ballistic missile submarine surveillance warheads are currently allowed to remain in this category.

Inactive Stockpile. Warheads retained in a nonoperational status for augmentation or replacement of warheads in the active stockpile. Tritium gas transfer systems, if installed, are removed and returned to NNSA prior to their projected limited life expiration. Hedge and logistics warheads are updated to incorporate the latest warhead Mods or Alts.

  • Inactive Hedge (RS 4) – Warheads retained for deployment to manage technological risks in the AR stockpile or to augment the AR stockpile in response to geopolitical developments. These warheads are available to deploy or upload per prescribed USSTRATCOM activation timelines.
  • Inactive Logistics (RS 5) – Warheads used for logistical and surveillance purposes. Warheads may be in various stages of disassembly.
  • Inactive Reserve (RS 6) – Warheads retained to provide a long-term response for risk mitigation of technical failings in current and future LEPs. Warheads in this category are exempt from future LEPs including Mods and Alts.

Figure 4.7 depicts the characteristics of each readiness state.

Readiness State Deployed LLCs
Installed
LEP (as
required)
Reliability
Assessed
Safety
Assessed
AS or
IS
RS 1: Active Ready AS
RS 2: Active Hedge   AS
RS 3: Active Logistics   AS
RS 4: Inactive Hedge     IS
RS 5: Inactive Logistics     IS
RS 6: Inactive Reserve         IS
Figure 4.7 Stockpile Readiness States

Logistical Planning

Logistical planning for configuration management ensures components, weapons movements, and locations are synchronized, as appropriate. Logistical planning includes plans for storing, staging, maintaining, moving, testing, and refurbishing weapons. Nuclear weapons logisticians must comply with requirements and restrictions from several sources, including joint DoD-NNSA agreements and memoranda of understanding, Joint Publications (JP) published by the Joint Chiefs of Staff, the Joint Nuclear Weapons Publications System (JNWPS),6 and regulations of the Military Departments. Logistical planning ensures weapons are handled, stored, and transported in ways that are safe, secure, and maintained so as to be reliable, with appropriate controls in place to preclude unauthorized acts or events.

Storage
Figure 4.8
Figure 4.8 Munitions Storage Igloo

Storage is the placement of weapons in a holding facility for an indefinite period of time. Nuclear weapons are amassed in secure weapons storage areas, most in munitions storage igloos (Figure 4.8). Logistical planning for nuclear weapons storage includes several critical considerations: the number of square feet required to store the designated warheads in each igloo so as to avoid nuclear criticality concerns; special barriers needed for safe separation of certain types of nuclear warheads; inside traffic flow for access to warheads by serial number for maintenance or movement of a surveillance sample; and procedures for allowing access and security, both within the exclusion area and at greater distances from the storage facility. Currently, storage of nuclear weapons occurs only at DoD facilities operated by the Navy and the Air Force. Storage is also a consideration for retired nuclear weapons awaiting dismantlement.

Staging

Staging refers to the placement of warheads awaiting some specific function (e.g., transportation, disassembly, or dismantlement) in a holding facility for a limited period of time. Nuclear weapons staging includes the logistical planning elements and the planned flow of warheads in the disassembly or dismantlement queue. Nuclear weapons are usually staged in secure areas awaiting disassembly or dismantlement at the Pantex Plant near Amarillo, Texas. Many current U.S. nuclear weapons have been staged in the disassembly queue at least once as surveillance samples, where they were disassembled, their components were tested and evaluated, and they were reassembled for return to the stockpile. Some warheads have been through this process several times.

Maintenance

Nuclear weapons maintenance includes the technical operations necessary to disassemble and reassemble a warhead to whatever extent is required for the replacement of one or more components. Maintenance operations require highly specialized training to qualify maintenance technicians as well as special ordnance tools, technical manuals, and secure and effective maintenance facilities. Most maintenance operations, including limited-life component exchanges (LLCEs), are performed by Navy or Air Force technicians and maintainers at an appropriate military nuclear weapons maintenance facility. Some maintenance operations require the warhead to be disassembled to a greater extent than military technicians are authorized; in this case, the warhead must be sent back to the Pantex Plant for maintenance.

NNSA establishes an LLCE schedule for each type of warhead. This schedule is managed by individual warhead and serial number and is coordinated between the appropriate Military Department and NNSA.

Movement

Nuclear weapons are moved for several reasons. Warheads may be moved for maintenance activities, or they may be moved within an operational base area. Warheads can be moved from an operational base to a depot upon retirement as part of the dismantlement queue, and they can be moved again to Pantex for actual dismantlement. Warheads may also be moved to the Pantex Plant for disassembly or returned from Pantex after re-assembly. On occasion, a warhead will be returned from DoD to Pantex because of a special maintenance problem. Normally, all warhead movements from one installation to another within the continental United States are accomplished using NNSA secure safeguards ground transport vehicles. The Air Force uses its own certified ground vehicles and security for moves within an operational base area. Movements of weapons to and from Europe are accomplished by the Air Force using certified cargo aircraft. LLCs may be transported by special NNSA contract courier aircraft or by NNSA secure safeguards transport vehicles. Representatives from agencies with nuclear weapons movement responsibilities meet frequently to coordinate the movement schedule.

Surveillance

The logistical aspect of the surveillance program include downloading, uploading, reactivating, and transporting warheads. For example, an active ready warhead selected at random to be a surveillance sample is downloaded from an ICBM. A logistics warhead is uploaded to replace the active ready warhead, with minimal loss of operational readiness. NNSA produces LLCs which are sent to the depot, and a replacement warhead is reactivated and transported by a secure safeguards transport vehicle to the operational base to replace the logistics warhead. The secure safeguards vehicle transports the surveillance sample warhead to Pantex for disassembly. After the surveillance testing is complete, the warhead may be reassembled and returned to the depot as an inactive warhead. Logisticians plan and coordinate the dates and required transport movements for each upload and download operation.

Forward Deployment

The United States remains committed to supporting NATO forces with nuclear weapons that are forward deployed in Europe. Recommendations for forward deployment are sent to the President as a Nuclear Weapons Deployment Plan. The President then issues a classified Nuclear Weapons Deployment Authorization (NWDA) as a directive, specifying the quantities and locations of U.S. forward-deployed weapons.

Life Extension Program

Weapon systems are being maintained well beyond their original design lifetimes. As these systems age, NNSA continues to detect anomalies that may ultimately degrade performance of some nuclear weapons to unacceptable levels. Life extension activities address these aging and performance issues, enhancing safety features and improving security, while meeting strategic deterrence requirements. Additional LEP goals are to reduce, to the extent possible, materials that are hazardous, costly to manufacture, degrade prematurely, or react with other materials in a manner that affects performance, safety, or security. A well-planned and well-executed stockpile life extension strategy improves safety and security while enabling DoD to implement a deployment and hedge strategy consistent with national security guidance. In addition, because of production constraints, NNSA uses both refurbished and reused components from legacy systems as well as newly manufactured parts. Changing materials, using components from legacy systems in new LEPs, and remanufacturing legacy component designs present significant challenges to today’s stockpile stewards.

Retired Warheads

Warheads are retired from the stockpile in accordance with presidential guidance in the NWSP. Retired warheads that are released for disassembly are scheduled for disassembly consistent with the throughput available in NNSA facilities so as not to impact support for DoD requirements. Currently, there is a backlog of weapons awaiting disassembly. Most of these warheads remain stored at DoD facilities because of limited staging capacity at NNSA facilities.

NNSA validates the safety of all retired warheads and reports annually to the Nuclear Weapons Council Standing and Safety Committee (NWCSSC) until the weapons are dismantled. These annual reports specify the basis for safety validation and may require additional sampling from the population of retired warheads. See Chapter 6: Nuclear Weapons Council for more information on the NWCSSC and NWC reports.

Stockpile Stewardship Program

The NNSA Stockpile Stewardship Program (SSP) was established by Presidential Directive 28 as a response to the National Defense Authorization Act for Fiscal Year 1994 (Public Law 103-160) which requires, in the absence of nuclear explosive testing, a program to:

  • support a focused, multifaceted program to increase the understanding of the enduring stockpile;
  • predict, detect, and evaluate potential problems of the aging stockpile;
  • refurbish and remanufacture weapons and components, as required; and
  • maintain the science and engineering institutions needed to support the U.S. nuclear deterrent, now and in the future.

In the past, underground nuclear testing and the continuous development and production of new nuclear weapons were essential to preserve high confidence in the stockpile. The United States has not manufactured a new weapon for over 30 years. The challenge for NNSA has been to maintain confidence in the nuclear weapons in the stockpile without producing new weapons or conducting nuclear explosive tests. The solution has been to field a suite of innovative experimental platforms, diagnostic equipment, and high-performance computers that build on past test data to simulate the internal dynamics of nuclear weapons. Armed with this understanding, the effects of changes to the current stockpile through either aging or component replacement may be understood through non-nuclear testing as well as modeling and simulation.

The SSP exercises the NNSA Nuclear Security Enterprise capabilities across the entire nuclear weapon life cycle that are critical for sustaining the deterrent into the future. The program also ensures proficiency of the NNSA workforce for the future and helps maintain the readiness of its infrastructure to support nearterm and future workloads. Finally, it provides foundational science, technology, and engineering (ST&E) and computational capabilities that serve as a hedge against prospective and unanticipated risks and technological surprise. Key activities include advanced modeling and simulation capabilities, subcritical and hydrodynamic experiments, high-energy-density physics experiments, and test flights in high-fidelity simulators, which provide the capabilities to underwrite the present day and future nuclear stockpiles.

Stockpile Management

Stockpile management refers to the cradle-to-grave activities related to all U.S. nuclear weapons. All stockpile management activities are coordinated by DoD and NNSA through the NWC. Stockpile management is the sum of the activities, processes, and procedures for the concept development, design engineering, production, quality assurance, fielding, maintenance, repair, storage, transportation, physical security, employment (if directed by the President), dismantlement, and disposal of U.S. nuclear weapons and associated components and materials. Stockpile management ensures the nuclear deterrent is safe, secure, reliable, and effective.

Stockpile Management Evolution

The U.S. approach to stockpile management has evolved over time to reflect the military and political realities of the international security environment as well as U.S. national security priorities and objectives. From 1945 to 1991, U.S. nuclear warheads were designed, developed, produced, deployed to the stockpile (usually for a period up to 15 to 20 years), and retired and dismantled, to be replaced by new, more modern weapons that generally offered unique military capabilities and better safety and security features. Figure 4.9 illustrates U.S. nuclear stockpile management during the Cold War. This continuous replacement cycle ensured U.S. nuclear weapons incorporated evolving technological advances and achieved the best military performance to counter the specific threats of the day.

Figure 4.9
Figure 4.9 U.S. Nuclear Stockpile Management During the Cold War

Figure 4.10
Figure 4.10 Cold War Nuclear Weapon
Delivery System Categories

During the Cold War, a primary objective of U.S. nuclear weapons design and development became maximizing the yield of the weapon in the smallest possible package, resulting in a maximum yield-to-weight ratio. Warheads built to achieve this goal were produced with cutting edge technology and manufactured with very tight tolerances. Warheads were designed to be carried by increasingly more sophisticated and capable delivery systems.7 A second objective was to incorporate modern safety and security features in the warheads, which added to the design complexity and level of production sophistication. A third objective was to achieve operational flexibility in the stockpile. At the height of the Cold War, the United States had more than 50 different types of nuclear weapons in five delivery categories (see Figure 4.10). This offered the President a wide range of options in the event nuclear weapons were needed.

The current stockpile is composed of a subset of these weapons. All of the weapons in the current stockpile were developed and produced during the Cold War and have exceeded the end of their originally planned life cycle.

Between the mid-1980s and the early 1990s, U.S. stockpile management strategies shifted significantly. The end of the Cold War in the late 1980s coincided with the closure of the Rocky Flats production facility.8 At that time, the United States adjusted its national security priorities and reconsidered the appropriate role of nuclear weapons in light of a desire to realize the benefits of the “peace dividend.” There was also an increasing awareness that nuclear proliferation and the possibility of a nuclear accident or nuclear terrorism were becoming the most urgent threats facing the United States and its allies.

In response to these changing geopolitical circumstances, President George H. W. Bush announced the immediate termination of additional nuclear weapons production in 1991 and a moratorium on underground nuclear explosive testing, which began in 1992 and has continued ever since. As a result, the nuclear weapons modernization and replacement model was abruptly terminated and supplanted by a mandate for the indefinite retention of the weapons in the legacy stockpile. To fulfill this mandate, stockpile management strategies evolved toward maintaining the legacy stockpile indefinitely.

Stockpile Life Extension from 1992–Present

By 1992, when warhead production and underground nuclear explosive testing ended, the designs of each type of weapon in the stockpile had been confirmed with nuclear testing, and U.S. nuclear scientists and engineers were confident in both the designs and manufacturing processes that produced the weapons. Because of this confidence, the primary stockpile management strategy to ensure the continued safety, security, and reliability of U.S. nuclear weapons was to maintain the weapons in the stockpile as closely as possible to their original designs and specifications. This has been achieved through stockpile life extension programs. During this period, each weapon-type in the enduring stockpile had LEPs planned as far into the future as practicable, in many cases up to two decades. LEP planning and the reductions in stockpile quantities associated with various arms control treaties led to a revised life cycle for nuclear weapons, as illustrated in Figure 4.11.

Figure 4.11
Figure 4.11 U.S. Approach to Stockpile Management, 1992–Present

LEPs, which have been conducted since the 1990s, involve the use of existing or newly manufactured non-nuclear components that are based on the original designs specific to that weapon. Non-nuclear components are produced or refurbished as closely as possible to the original designs for a specific warhead. Deviations from original designs are often the result of “sunset” technologies (where there are no longer technologies in existence to produce items) or manufacturing processes and the use of alternate materials that cannot be replicated because of environmental or health hazards.

There are two increasingly challenging issues with a life extension-only stockpile maintenance strategy. First, as a growing number of incremental changes are made to nuclear weapons through the life extension process, the further away from their original underground nuclear test (UGT)-validated specifications the weapons become. Because these legacy weapons were built to push the envelope of what was technologically possible in terms of achieving yield-to-weight ratios, very little margin for error exists; any deviations from very exact specifications could negatively impact confidence in the performance of the weapon. As confidence degrades and uncertainty is introduced, it becomes increasingly difficult to certify that these weapons continue to meet safety, security, and yield requirements. In light of the underground explosive testing moratorium, the LEP process by itself limits the U.S. ability to understand how new technologies would interact with the existing safety, security, and yield characteristics of the legacy weapons.

The second issue is that life extension offers little opportunity to enhance safety, security, or military performance through the introduction of modern technological improvements. Currently fielded stockpile weapons have features that were developed in the 1970s and 1980s. Today, the United States has the technical capability to enhance safety, security, and military performance relative to current weapons. For example, increasing the accuracy of warheads could result in the need for lower yields to achieve similar military effects.

Advancement of Stockpile Life Extension

The United States has understood the value of flexibility for nuclear deterrence for six decades, but its importance is now magnified by the emerging diversity of nuclear and non-nuclear strategic threats and the dynamism and uncertainties of the security environment.

The United States has a two-pronged approach to maintaining the stockpile: first, the operational lives of legacy weapons are being extended to the extent practicable; second, the United States is planning to begin to replace warheads in the existing stockpile by the early 2030s.

Stockpile Evaluation and Quality Assurance

As part of the nuclear weapons life cycle, weapons in the U.S. stockpile are surveilled for the purpose of evaluation and quality assurance. Issues with a nuclear weapon-type or nuclear weapon family have occurred in the past as a result of design and/or production problems, but each of the weapon-types in the current U.S. stockpile have undergone underground nuclear explosive testing during their original production runs. As a result, there is high confidence that all of the legacy Cold War weapons in the current U.S. stockpile were designed and produced to be safe and reliable.

Today, however, the aging of components-both nuclear and non-nuclear-cause the majority of the problems and concerns that lead to requirements for warhead Alts and Mods. These problems may be detected as a result of evaluations during stockpile surveillance that includes non-nuclear flight and laboratory testing and/or observations made by field maintenance technicians. A weapon may also undergo an Alt or a Mod because of changes in the mechanical or electrical interface between a warhead and its delivery system, rather than as a result of a problem or issue affecting safety or reliability.

In order to detect problems or issues in a timely manner, and to ensure that they are resolved as quickly and efficiently as possible, NNSA has a formal stockpile evaluation program for quality assurance. The NNSA surveillance program has evolved over the years, but has so far been successful in identifying and resolving issues affecting the overall credibility of the U.S. nuclear deterrent.

History of Stockpile Evaluation

The Manhattan Project, which produced one test device and two war reserve (WR) weapons, Little Boy and Fat Man, employed to end World War II, had no formal, structured Quality Assurance (QA) program and no safety standards or reliability requirements to be met. Rather, quality was assured through the knowledge and expertise of weapons scientists and engineers. History proves the Manhattan Project approach to quality was successful in that it accomplished an extremely difficult task without a catastrophic accident.

The first nuclear weapons required in-flight insertion (IFI) of essential nuclear components, until which time the weapons were unusable, making them inherently safe. Once assembled in flight, the weapons had none of the modern safety features that preclude an accidental detonation. The early focus was on ensuring the reliability of the weapons given that they would not be assembled until they were near the target. In the early 1950s, as the U.S. nuclear weapons capability expanded into a wider variety of delivery systems and, because of an emphasis on more rapid response times for employment, IFI became impractical. The development of sealed-pit weapons to replace IFI weapons led to requirements for nuclear detonation safety features to be built into the warheads.9 See Chapter 8: Nuclear Surety for a detailed discussion of nuclear detonation safety and security standards.

During this time, the concern for safety and reliability caused the expansion of QA activities into a program that included random sampling of approximately 100 warheads of each type, each year. Tests were conducted to detect and repair problems related to design and/or production processes. The warheads that were randomly sampled were used for both laboratory and flight testing and provided a sample size to calculate reliability and stress-test the performance of key components in various extreme environments. This sample size was unsustainable for the long term, and, within a year or two of entering full production, the sample size was reduced to a random sampling of 44 warheads. This sample size was adequate to calculate reliability for each warhead-type. Within a few more years, the number was reduced to 22 per year. Eventually, the sample number was reduced to 11 per year to reflect fiscal and logistical realities. Each weapon system was re-evaluated on a case-by-case basis with respect to the approach to its sampling, accounting for the specific technical needs of each system and new approaches to evaluation tests that were being developed and implemented. As a result, some system samples were reduced from 11 per year to lower numbers.

Surveillance Program

In the mid-1980s, DOE strengthened the significant finding investigation (SFI) process, which was the method by which anomalous findings were identified and reported. Since then, any anomalous finding or suspected defect that might negatively impact weapon safety or reliability is documented as an SFI. Weapon system engineers and surveillance engineers investigate, evaluate, and resolve SFIs.

At the national level, warheads drawn from the fielded stockpile as random samples are considered part of the NNSA surveillance program. Under this program, additional efficiencies are gained by sampling and evaluating several warhead-types as a warhead “family” if there are enough identical key components. Now as a rule, each warhead family has 11 random samples evaluated each year under what used to be called the Quality Assurance and Reliability Testing (QART) program. This sample size enables the quality assurance program to provide an annual safety validation, supply a reliability estimate semi-annually, and identify any randomly occurring problem present in 10 percent or more of that warhead-type with a 90 percent assurance, within two years of occurrence.

Weapons drawn for surveillance sampling are returned to the Pantex Facility for disassembly. Generally, of the samples selected randomly by serial number, two to three are used for flight testing and the remainder are used for laboratory testing and/or component and material evaluation. Surveillance testing and evaluation may be conducted at Pantex or at other NNSA facilities. Certain components are physically removed from the weapon, assembled into test configurations, and subjected to electrical, explosive, or other types of performance or stress testing. The condition of the weapon and its components is carefully maintained during the evaluation process. The integrity of electrical connections remains undisturbed whenever possible. Typically, one sample per warhead family per year is subjected to non-nuclear destructive testing of its nuclear components and cannot be rebuilt. This is called a destructive test or “D-test” and the specific warhead is called a “D-test unit.” Depending on the availability of non-nuclear components and the military requirement to maintain stockpile quantities, the remaining samples may be rebuilt and returned to the stockpile.

Today, the goals of the U.S. nuclear weapons quality assurance programs are to validate safety, ensure required reliability, and detect or, if possible, prevent problems from developing for each warhead-type in the stockpile. Without nuclear explosive testing, the current stockpile of nuclear weapons must be evaluated for QA only through the use of non-nuclear testing, surveillance, and, to the extent applicable, modeling and simulation efforts. NNSA surveillance activities provide data to evaluate the condition of the stockpile in support of annual assessments of safety, security, reliability, and performance. In addition, the cumulative body of surveillance data supports decisions regarding weapon life extensions, Mods, Alts, repairs, and rebuilds.

As warheads in the stockpile age, stockpile evaluation has detected a number of problems and areas of potential future concern that so far have been managed.

These problems, together with national security policy decisions, have led to expanded life extension programs and planned replacement programs while surveillance continues to assess the quality of products during life extension. During life-extension production, the surveillance activity is robust in order to detect design, material, production, and other assurance related issues.

Surveillance requirements, as determined by the national security laboratories for the weapon systems, in conjunction with NNSA, Air Force, and Navy for joint testing, result in defined experiments to acquire the data that support the NNSA surveillance program. The national security laboratories, in conjunction with NNSA and the nuclear weapons production facilities, continually refine these requirements based on new surveillance information, annual assessment findings, and analysis of historical information using modern assessment methodologies and computational tools.

The current NNSA surveillance program has four primary goals:

  1. Understand the state of weapons in the U.S. stockpile today (core surveillance activities).
  2. Predict the state of weapons in the future (enhanced surveillance activities).
  3. Maintain the capabilities to surveil the stockpile.
  4. Enhance the capabilities to surveil the stockpile.

Each weapon-type and/or family is considered on a case-by-case basis, so that highly reliable systems might be subject to fewer tests, while weapon-types that have begun to display age-related issues might be given increased scrutiny. The objective is to ensure that surveillance resources are allocated appropriately and that a compelling sampling rationale is developed for each weapon-type or family.

This risk-based approach to surveillance ensures that issues will continue to be identified and resolved as quickly and effectively as possible as the weapons in the U.S. nuclear deterrent age well beyond their original design lives and beyond the data obtained from underground nuclear explosive testing and the experience of U.S. scientists and engineers.

The current NNSA stockpile surveillance program is comprised of two major elements that work closely together: the New Material and Stockpile Evaluation (NMSE) program, whose goal is to understand the current state of the stockpile; and the Aging and Lifetimes (A&L) program, whose goal is to predict the future state of the aging stockpile. Both programs are located within the Office of Engineering and Technology Maturation. The NMSE program conducts surveillance evaluations of both the existing stockpile (i.e., stockpile returns) and newly refurbished LEP weapons. The mission of the A&L program, formerly known as the enhanced surveillance program, is to detect the onset of deleterious aging phenomena in weapon materials, components, or subsystems in time to execute corrective actions before they degrade the nuclear deterrent. The A&L program contributes to weapon safety, performance, and reliability by providing the tools needed to predict material, component, and subsystem lifetimes and detect the precursors of potential age-induced defects. These two programs work closely together to execute the surveillance program and are constantly striving to develop new and better surveillance capabilities and techniques.

New Material and Stockpile Evaluation Program

The NMSE program has the following four goals:

  1. Identify defects that affect safety, security, performance, and reliability.
  2. Establish margins between design requirements and performance at the component and material level.
  3. Identify changes and aging trends at a component and material level.
  4. Develop the capability for predictive assessments of stockpile components and materials.

The NMSE program consists of planning for and conducting tests of WR hardware, or hardware considered to be representative of WR products. The NMSE program provides critical data to evaluate the safety, security, performance, and reliability of the current condition of the active and inactive stockpiles and to inform decisions about the stockpile.

The evaluations conducted as part of the NMSE program are either systemlevel tests or laboratory tests. System-level testing can be high-fidelity joint test assemblies (JTAs), instrumented JTAs, Weapons Evaluation Test Laboratory (WETL) testbeds, or joint integrated laboratory test (JILT) units. System-level tests may occur jointly with the Air Force or the Navy and use combinations of existing weapons and/or new production units, which are modified into JTAs. Some JTAs contain extensive telemetry instrumentation, while others contain high-fidelity mock nuclear assemblies to recreate, as closely as possible, the mass properties of WR weapons. Stockpile laboratory tests conducted at the component level assess major assemblies and components and, ultimately, the materials that make up the components (e.g., metals, plastics, ceramics, foams, and explosives). This surveillance process enables detection and evaluation of aging trends and anomalous changes at the component or material level. The NMSE program consists of four elements:

  1. Disassembly and Inspection – Weapons sampled from the production lines or returned from DoD are inspected during disassembly. Weapon 66 Nuclear Matters Handbook 2020 disassembly is conducted in a controlled manner to identify any abnormal conditions and preserve the components for subsequent evaluations. Visual inspections during dismantlement can also provide “state-of-health” information.
  2. Flight Testing – After disassembly and inspection, selected weapons are reconfigured into JTAs and rebuilt to represent the original build to the extent possible. However, all special nuclear material (SNM) components are replaced with either surrogate materials or instrumentation. The JTA units are flown by the DoD operational command responsible for the system. JTA configurations vary from high-fidelity units, which essentially have no onboard diagnostics, to fully instrumented units, which provide detailed information on component and subsystem performance.
  3. Stockpile Laboratory Testing – Test bed configurations are built to enable prescribed function testing of single parts or subsystems using parent unit hardware from stockpile weapon returns. The majority of this testing occurs at the WETL, which is operated by Sandia National Laboratories at Pantex and involves electrical and mechanical testing of the systems. The JILT facility, located at Hill Air Force Base in Utah, and WETL also conduct evaluations of joint test beds to obtain information regarding delivery system-weapon interfaces.
  4. Component Testing and Material Evaluation – Components and materials from the disassembly and inspection process, or Shelf Life Program, undergo further evaluations to assess component functionality, performance margins and trends, material behavior, and aging characteristics. This testing can involve both non-destructive evaluation techniques (e.g., radiography, ultrasonic testing, and dimensional measurements) and destructive evaluation techniques (e.g., tests of material strength and explosive performance as well as chemical assessments).

Aging and Lifetimes Program

The A&L program pursues three principal goals:

  1. Provide timely warning of aging phenomena that threaten the effectiveness of the nuclear stockpile.
  2. Provide diagnostic tools and methods for improving effective and efficient stockpile evaluation of the enduring and future stockpiles.
  3. Inform and enable age-aware design, manufacture, and surveillance decisions for stockpile modernization.

A desired outcome of this new process is to make surveillance (a) more predictive (i.e., using reliable predictive modeling and performance codes), (b) use less invasive/destructive testing, and (c) more cost effective by preserving precious overall subsystems and components from the weapons. A&L personnel at the national security laboratories and nuclear weapons production facilities collaborate and partner with NMSE personnel as many A&L diagnostic development activities lead to capabilities (i.e., test equipment, analysis techniques, and computational simulations) that are ultimately deployed in the NMSE program.

Dual-Agency Responsibility for Stockpile Management

The responsibilities for nuclear weapons management and development were originally codified in the Atomic Energy Act of 1946, which reflected congressional desire for civilian control over the uses of atomic (nuclear) energy and established the Atomic Energy Commission (AEC) to manage the U.S. nuclear weapons program. Basic departmental responsibilities and the development process were specified in the 1953 Agreement Between the AEC and the DoD for the Development, Production, and Standardization of Atomic Weapons, commonly known as the “1953 Agreement.”

In 1974, an administrative reorganization transformed the AEC into the Energy Research and Development Agency (ERDA). A subsequent reorganization in 1977 created the Department of Energy. At the time, the Defense Programs (DP) portion of DOE assumed the responsibilities of AEC/ERDA. In 1983, DoD and DOE signed a Memorandum of Understanding (MOU), Objectives and Responsibilities for Joint Nuclear Weapon Activities, providing greater detail for the interagency division of responsibilities. In 2000, the NNSA was established as a semi-autonomous agency within DOE responsible for the U.S. nuclear weapons complex and associated nonproliferation activities. Figure 4.12 illustrates the evolution of the AEC to NNSA. Figure 4.13 illustrates the timeline of basic DoD-DOE nuclear weapons laws and agreements.

Figure 4.12
Figure 4.12 AEC to NNSA
Figure 4.13
Figure 4.13 Timeline of DoD-DOE Nuclear-Related Agreements

While the fundamental dual-agency division of responsibilities for nuclear weapons has not changed significantly, the 1953 Agreement was supplemented in 1977 to change the AEC to the ERDA, again in 1984 to incorporate the details of the 1983 MOU, and most recently in 1988 to incorporate the then newly established NWC.

The NWC serves as the focal point for inter-agency analyses and decisions to sustain and modernize the U.S. nuclear deterrent, maintain and manage the stockpile, and ensure alignment between DoD delivery system programs and NNSA weapons programs. See Chapter 6: Nuclear Weapons Council for additional information.

Departmental Responsibilities

DoD is responsible for the acquisition of delivery platforms and vehicles. DoD is also responsible for identifying the requirements that drive the retention of existing weapons associated with these systems and the need for modifications or new weapons. DoD is responsible for operational employment preparedness, security, accountability, and logistical maintenance of weapons in DoD custody. Overall, NNSA is responsible for developing, producing, certifying, and maintaining nuclear weapons.

  • participating in authorized concept and feasibility studies;
  • developing requirements documents that specify operational characteristics for each warhead-type and the environments in which the warhead must perform or remain safe;
  • participating in the coordination of the engineering interface requirements between the warhead and the delivery system;
  • determining design acceptability;
  • specifying military/national security requirements for specific types and quantities of warheads;
  • receiving, transporting, storing, securing, maintaining, and, if directed by the President, employing fielded warheads;
  • accounting for individual warheads in DoD custody;
  • participating in the joint nuclear weapons decision process (including the NWC, the NWCSSC, working groups, and the warhead joint DoDNNSA POG);
  • developing and acquiring the delivery vehicle and launch platform for a warhead; and
  • storing retired warheads awaiting dismantlement in accordance with jointly approved plans.

NNSA is responsible for:

  • participating in authorized concept and feasibility studies;
  • evaluating and selecting the baseline warhead design approach;
  • determining the resources (e.g., funding, nuclear and non-nuclear materials, human capital, facilities) required for the program;
  • performing development engineering to establish and refine the warhead design;
  • engineering and establishing the required production lines;
  • producing or acquiring required materials and components;
  • assembling components and sub-assemblies into stockpile warheads (if approved by the President);
  • providing secure transport within the United States;
  • developing maintenance procedures and producing replacement LLCs and replacement components;
  • conducting a jointly approved quality assurance program;
  • developing LEPs, when required, for sustaining the stockpile;
  • securing warheads, components, and materials while at NNSA facilities;
  • accounting for individual warheads in NNSA custody;
  • participating in the joint nuclear weapons decision process;
  • receiving and dismantling retired warheads; and
  • disposing of components and materials from retired warheads.

Chapter 4 collage

1 The earliest U.S. nuclear weapons were distinguished by Mark (MK) numbers, derived from the British system for designating aircraft. In 1949, the MK5 nuclear weapon, intended for the Air Force surfaceto- surface Matador cruise missile and the Navy Regulus I cruise missile, had delivery system interface engineering considerations that were not common to gravity bombs. A decision was made to designate the weapon as a warhead, using the term W5. At the programmatic level, the joint DoD-NNSA Project Officers Group (POG) distinguishes between warheads and bombs and weapons are designated accordingly.


2 U.S. Strategic Command, the Military Departments, and other Combatant Commanders recommend the numbers and types of operational nuclear weapons required to satisfy national security policy objectives. These numbers, combined with the NNSA capability and capacity to support surveillance, maintenance, and life extension, result in stockpile projections over time. These projections are codified in the annual NWSP issued by the President. See Chapter 6: Nuclear Weapons Council for more information.


3 Tritium is a radioactive gas used in U.S. warheads as a boosting gas to achieve required yields. Because tritium is in limited supply and very expensive, special procedures are used to ensure none is wasted in the process of storing, moving, and maintaining warheads. The national repository for tritium is at the Savannah River Site, located near Aiken, South Carolina.


4 Surveillance is the term used to describe the activities to ensure weapons continue to meet established safety, security, and reliability standards. Surveillance involves system and component testing and is conducted with the goal of validating safety, estimating reliability, and identifying and correcting existing or potential problems with the weapons. As the stockpile continues to age well beyond its original planned life, the quality assurance approach has been expanded to include planned replacement for many key components before they begin to degrade in performance.


5 Hedge or contingency weapons available for redeployment over time.


6 JNWPS is a system of technical manuals on nuclear weapons, associated materiel, and related components. It includes general and materiel manuals developed by DoD and NNSA to provide authoritative nuclear weapons instructions and data.


7 The first nuclear delivery system, the Enola Gay, was a specially modified long-range bomber. Since 1945, the United States has added ICBMs and SLBMs to its nuclear triad. For additional information on nuclear delivery systems, see Chapter 3: Nuclear Delivery Systems.


8 The Rocky Flats Plant in Colorado was the only U.S. facility that mass-produced plutonium pits. It was closed as a result of violating environmental protection laws. Reestablishing a pit production capability (including plutonium processing) and building a modern secondary production facility are necessary steps for NNSA to achieve a modern and responsive capacity to produce nuclear components. This will mark the beginning of a new stockpile support paradigm whereby NNSA can meet stockpile requirements through its production infrastructure, rather than through the retention of inactive stockpile weapons to serve as a hedge and support Military requirements.


9 Sealed-pit warheads are the opposite of IFI; they are stored and transported with the nuclear components assembled into the warhead and require no assembly or insertion by the military operational delivery unit prior to employment.