Nuclear Weapons

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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. Today, NNSA maintains the stockpile through the application of science, technology, engineering, high-speed computing, and manufacturing efforts within its Stockpile Stewardship Program. Ongoing life extension programs (LEPs), modifications (Mods) and alterations (Alts) of nuclear weapon systems have resulted in the United States entering an era of both delivery system and weapon modernization.

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 and 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. Figure 4.1 is a comprehensive list of warhead types and their descriptions.

Comprehensive List of Warhead-Types and Descriptions
Figure 4.1 Comprehensive List of Warhead Types and their Descriptions

Throughout the history of nuclear weapons development, the United States has produced families of warheads based on a single-warhead design. Significant enough differences between a bomb or warhead variant, per direction from NNSA, result in further identification as a modification (Mod) 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 the B61-3, B61-4, and B61-7 variants of the B61, is currently in the first production phase of the Phase 6.X Process. 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.

During the decision-making process, which includes consideration of military requirements and existing weapon performance characteristics by NNSA, a variant may not meet the threshold for designation as a Mod. In such cases, a variant will be designated as a weapon alteration (Alt). For example, the B61-4 Alt 370 introduced and implemented improved surety features through field retrofits. These improvements were not deemed significant enough to warrant a Mod increment (e.g., to something like B61-13).

All nuclear weapons in the stockpile are categorized 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 non-strategic 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. Figure 4.2 illustrates U.S. nuclear weapons and associated delivery systems, both current and future.

Figure 4.2
Figure 4.2 U.S. Nuclear Weapons and Associated Delivery Systems

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 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. 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. Stockpile components continue to be considered for new manufacture, reuse, or refurbishment. Figure 4.3 delineates the ages of the weapons in the current stockpile.

Date of
Entry into
First Prod.
FPU5 for
Age at Initial
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
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
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 4.3 Aging of the Legacy Stockpile

Figure 4.4 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
Figure 4.4 Current and Near-Future Nuclear Delivery Systems and Associated Weapons

Stockpile Quantities

While the United States has continued to reduce the number 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.

Stockpile quantities are authorized annually by presidential directive that specifies quantities of warheads, by type and by year, for a multi-year period. Figure 4.5 illustrates U.S. warhead production from the 1940s through the 2020s.

Figure 4.5
Figure 4.5 U.S. Warhead Production from the 1940s through the 2020s
(There have been no new warhead-types produced since the 1980s.)

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 4.6 shows stockpile quantities between 1962 and 2017.

Figure 4.6
Figure 4.6 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. The DoD and NNSA have procedures in place to mitigate these and other risks with strategies that account for threats to the stability of the nuclear deterrent at lower stockpile levels.

Basic approaches to stockpile risk mitigation include: the existence of an active and versatile warhead production capability, which existed prior to 1991; maintenance of warheads identified to counter significant unforeseen events, which have been maintained since 1991; or some combination of the two. Maintaining warheads to counter unforeseen events is referred to as a “hedge.” 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 that have been successfully maintained beyond their design lifetimes, for significantly evolved roles and missions.

Modern stockpile configuration involves maintaining aging weapons in an environment where they cannot be replaced once dismantled or 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 quantity of deployed weapons together with those that could be deployed if needed.2

All U.S. nuclear weapons are not ready for immediate use, and balancing the various operational requirements against physical, logistical, and fiscal realities is challenging. Summarily, 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 warhead status to be filtered into different categories. Operational warheads are called the active stockpile. An active stockpile weapon is maintained with all War Reserve components emplaced. Nonoperational warheads are called the inactive stockpile, do not maintain limited life components (LLCs), and require varying degrees of attention to attain active status. Based on employment plans, strategic requirements, and logistical requirements, the NWSP specifies weapon configuration quantities 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), at intervals driven by design life. Active stockpile warheads are also refurbished with required LEP upgrades, evaluated for reliability estimates, and validated for safety. These warheads may be stored at a depot, operational base, or uploaded on a delivery vehicle.

Active stockpile warheads are sub-categorized to 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 may not be 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 may also be evaluated for reliability estimates. All inactive stockpile warheads are validated for safety, and are typically 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 4.7
Figure 4.7 Warhead Readiness States

A warhead readiness state (RS) maps the configuration of the weapons in the active and inactive stockpiles to simpler nomenclature for bookkeeping purposes. Figure 4.7 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 (CCM) requirements for operational warheads are met and are updated to incorporate the latest warhead refurbishment—Mods or Alts. CCMD orders specify the allocation of operational warheads and readiness timelines. The three RS levels for the active stockpile are:

  • 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.

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. The three RS levels for the inactive stockpile are:.

  • 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 4.8 depicts the characteristics of each readiness state.

Readiness State Deployed LLCs
LEP (as
AS or
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 4.8 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.


Figure 4.9
Figure 4.9 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 4.9). Logistical planning for nuclear weapons storage includes several critical considerations: the number of square feet required to store the designated warheads in each igloo to avoid nuclear criticality concerns; special barriers needed for safe separation of certain types of nuclear warheads; inside traffic flow for access to warheads 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 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.


Nuclear weapon maintenance includes the technical operations necessary to disassemble and reassemble a warhead to the extent required for replacement of one or more components. Maintenance operations require highly specialized training, ordnance tools, technical manuals, and facilities. Most maintenance operations, including limited-life component exchanges (LLCEs), are performed by Navy or Air Force technicians and maintainers at an appropriate military facility. Some maintenance operations require disassembly to a greater extent than military technicians are authorized; in this case, the warhead is returned to the Pantex Plant for maintenance.

NNSA establishes an LLCE schedule for each type of warhead. This schedule is managed by warhead serial number and is coordinated between DoD and NNSA.


Nuclear weapons are moved for several reasons. Warheads may be moved for maintenance activities, internal base logistics, or between locations. Warheads can be moved from an operational base to a depot as part of the dismantlement queue, and again to Pantex for actual dismantlement. Warheads may also be moved to, or from, the Pantex Plant for maintenance, repair, or for surveillance. 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 weapon movements within an operational base. Movements of weapons between the U.S. and Europe are accomplished via Air Force certified aircraft. LLCs may be transported by special NNSA contract courier aircraft or by NNSA secure safeguards transport vehicles. Movement schedules are coordinated frequently between appropriate agency personnel.


The logistical aspects of the surveillance program include downloading, uploading, reactivating, and transporting warheads. For example, an AR warhead randomly selected as a surveillance sample is downloaded from an ICBM. A logistics warhead is uploaded to replace the AR 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 through the forward deployment of nuclear weapons 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.

Life Extension Program

Weapon systems are being maintained well beyond their original design lifetimes. As these systems age, NNSA is responsible for detecting anomalies that negatively impact safety, reliability, and effectiveness of the stockpile as part of the annual assessment process. Life extension activities address 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, NNSA leverages refurbished and reused components, where practical, along with newly manufactured parts. Changing materials, component reuse, and remanufacturing components to legacy 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 and in accordance with DoD requirements.

NNSA validates the safety of all retired warheads and reports annually to the Nuclear Weapons Council Standing and Safety Committee (NWCSSC). 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 in 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 nation’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 conducting nuclear explosive tests. The solution has been to field a suite of innovative experimental platforms, diagnostic equipment, and high-performance computers used to capture and simulate nuclear weapon performance. Experimental data, ongoing model validation, and computational improvements contribute to understanding the effects of changes to the stockpile due to aging, component replacement, or modernization efforts; thus, bolstering an SSP approach that does not require nuclear testing.

The SSP exercises NNSA Nuclear Security Enterprise capabilities across the entire nuclear weapon life cycle critical for sustaining the deterrent into the future. The program also ensures proficiency of the NNSA workforce and helps maintain the readiness of its infrastructure to support near- and long-term activities. 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, subcritical and hydrodynamic experiments, high-energy-density physics experiments, and flight tests.

Stockpile Management

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

The U.S. approach to managing the stockpile has evolved over time to reflect military and political realities of the international security environment as well as U.S. national security priorities and objectives. Prior to 1992, U.S. nuclear warheads were managed per the process shown in Figure 4.10. This process was wrapped around confidence gained through nuclear testing, and was regularly exercised to incorporate modernized weapons that generally offered unique military capabilities and improved safety and security features that addressed specific threats of the day.

Figure 4.10
Figure 4.10 U.S. Nuclear Stockpile Management During the Cold War

Figure 4.11
Figure 4.11 Cold War Nuclear Weapon
Delivery System Categories

A primary objective of U.S. nuclear weapon design and development became maximizing the yield of the weapon in the smallest possible package (yield-to-weight ratio). Warheads built to achieve this goal were produced with cutting edge technology and manufactured with extremely tight tolerances. Warheads were designed to be carried by increasingly sophisticated and capable delivery systems. A second objective was to incorporate modern safety and security features in the warheads, which increased design and production complexity. 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 4.11), offering a wide range of options for deterrence and in the event of nuclear war. The current stockpile is composed of a subset of these weapons.

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.

A significant stockpile management strategy shift occurred during the decade leading up to the end of the Cold War, accompanied by the closure of the Rocky Flats production facility.7 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 at that time.

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 has been comported to since 1992. 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

Nuclear weapon performance confidence was long established via underground nuclear testing. To ensure the continued safety, security, and reliability of U.S. nuclear weapons, the SSP transitioned such that the stockpile is maintained as closely as possible to original design intent and performance characteristics. 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, according to a revised life cycle for nuclear weapons, as illustrated in Figure 4.12.

Figure 4.12
Figure 4.12 U.S. Approach to Stockpile Management, 1992–Present

LEPs employ 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 technologies that can no longer be acquired or produced. Often times, the use of alternate materials is required due to environmental or health hazards.

LEPs will be accompanied in the future, by full phase design, development, and manufacturing of weapons. For example, DOE/NNSA is now coordinating with DoD on specific requirements and design options for the W93 program of record. In the FY 2021 SSMP, Stockpile Major Modernization was renamed from the Life Extension Programs (LEPs) and Major Alterations (Alts) Program in the DOE/NNSA’s Directed Stockpile Work Program budget restructure and contains the subprograms of: (1) B61 LEP; (2) W88 Alteration Program; (3) W80-4 LEP; (4) W87-1 Modification Program; and (5) W93. Stockpile Major Modernization encompasses the programs necessary to meet DoD warhead modernization requirements and for the projected 20- to 30-year in-service life. The increased budget request for Stockpile Major Modernization principally represents the planned ramp-up of the W80-4 LEP to accomplish Phase 6.3 (Development Engineering) activities, Conceptual Design Reviews, production of warhead simulators/test units, and hydrodynamic physics tests to support nuclear certification; the planned ramp-up of the W87-1 Modification Program across all areas to complete Phase 6.2 (Feasibility Study and Design Options) deliverables before entry into Phase 6.2A (Design Definition and Cost Study); and the W93 planned Phase 1 (Concept Assessment) and refinement activities. For example, the W93 will incorporate modern technologies to improve safety, security, and flexibility to address future threats and will be designed for ease of manufacturing, maintenance, and certification.

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 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 these systems were designed and produced to be safe and reliable.

Today, however, component age and corrosion cause the majority of the issues that lead to warhead Alts and Mods. These problems are detected through stockpile surveillance, including non-nuclear flight and laboratory testing, or field maintenance observations. A weapon may also undergo an Alt or a Mod because of changes in interfaces between a warhead and its delivery system or the introduction of new delivery systems rather than as a result of issues affecting safety or reliability.

In order to detect 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, and has been successful in its execution.

Stockpile Surveillance

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 are randomly drawn from the fielded stockpile as 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. As a rule, each warhead family has 11 random samples evaluated. 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 Plant for disassembly. Generally, 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 prevent problems from developing for each warhead-type. Without nuclear explosive testing, the nuclear stockpile must be evaluated for QA only through the use of non-nuclear testing, surveillance, and modeling and simulation efforts. NNSA surveillance activities provide data to evaluate the condition of the stockpile in support of annual weapon assessments. 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.

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.

Surveillance requirements, as determined by the national security laboratories, 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, 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 six goals:

  1. Identify manufacturing and design defects that affect safety, security, performance, or reliability.
  2. Assess appropriate risks to the safety, security, and performance of the stockpile.
  3. Determine the margins between design requirements and performance at the component and material levels.
  4. Identify aging-related changes and trends at the subsystem or component and material levels.
  5. Further develop capabilities for predictive assessments of stockpile components and materials.
  6. Provide critical data for the annual Weapons Reliability Report and the Report on Stockpile Assessments.

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.

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, beyond the data obtained from underground nuclear explosive testing, and beyond the experience of U.S. scientists and engineers.

DOE/NNSA continually refines stockpile evaluation activity planning requirements based on new surveillance information, deployment of new diagnostic tools, annual assessment findings, and analysis of historical information using modern assessment methodologies and computational tools. Stockpile evaluations are conducted through weapon disassembly and inspection, stockpile flight testing, stockpile laboratory testing, component testing, and material evaluation and are detailed below.

  • Disassembly and Inspection (D&I) – Weapons sampled from the production lines or returned from DoD are inspected during disassembly. Weapon 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.
  • Stockpile Flight Testing – After D&I, selected weapons are reconfigured into joint test assemblies (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.
  • 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 Weapons Evaluation Test Laboratory (WETL), which is operated by Sandia National Laboratories at Pantex and involves electrical and mechanical testing. The Joint Integrated Laboratory Test (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.
  • Component Testing and Material Evaluation – Components and materials from the D&I 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).

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 4.13 illustrates the evolution of the AEC to NNSA. Figure 4.14 illustrates the timeline of basic DoD-DOE nuclear weapons laws and agreements.

Figure 4.13
Figure 4.13 AEC to NNSA
Figure 4.14
Figure 4.14 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, the need for modifying existing weapons, or the need for new weapons. DoD is responsible for operational employment preparedness, security, accountability, and logistical maintenance of weapons in DoD custody.

Specifically, DoD is responsible for:

  • 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 DoD-NNSA 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.

Overall, NNSA is responsible for developing, producing, certifying, and maintaining nuclear weapons. Specifically, 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 surface-to-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 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.