Historically, confidence in the effectiveness of all U.S. nuclear weapons was founded upon the perpetual modernization and upgrade of the warhead-types in the stockpile. This modernization program was achieved through constant research and development efforts, the regular production of new warheads to replace aging weapons, and the incorporation of improved safety features. In addition, the United States utilized a complementary combination of non-nuclear and nuclear testing to certify weapon designs and production processes, as well as to detect defects and validate repairs.

The United States produced its last new nuclear weapon in 1991 and performed its last Underground Nuclear Test (UGT) in 1992. The Presidential decision to stop testing and to terminate weapons production resulted in a paradigm shift that required significant adjustments in the U.S. approach to nuclear weapons stockpile management.

The National Nuclear Security Administration’s Stockpile Stewardship Program (SSP) was established in response to the 1994 National Defense Authorization Act (Public Law 103-160) which requires, in the absence of nuclear testing, a program to:

In order to certify the safety and reliability of the nation’s nuclear stockpile, the main goal of the SSP became the development of improved computer models and advanced experimental capabilities, thus providing accurate predictive capability of weapon performance.

As a result, confidence in the performance of weapons is now maintained through an ongoing process of three interconnected major program elements: stockpile surveillance, assessment and certification, and refurbishment.

• Stockpile Surveillance. Stockpile surveillance focuses on assessing the condition of weapons and understanding the effects of aging. Because aging affects the physical characteristics of materials, we must determine how these changes affect weapon safety and performance. With a better understanding of aging – together with the development of new diagnostic tools and improved analysis methods – stockpile surveillance can be more predictive, making it possible to correct developing problems. Since subtle changes to the weapons system may cause safety, reliability, or performance issues, early detection is critical.

• Assessment and Certification. Assessments of the safety and performance of stockpiled weapons and actions taken to modify them must be based on demonstrated performance. That is, the assessments must be grounded on existing nuclear test data, nonnuclear tests, fundamental science experiments, and simulations using validated computer models. To the extent possible, nonnuclear tests are used to assess weapon safety and performance and, together with past nuclear test results, are used to validate computer simulations. Once validated to the extent possible, these simulations guide expert judgments about stockpile issues.
  
  Such demonstration-based assessments underpin both the certification of a refurbished weapon system and the Annual Assessment Review. Mandated by law, this annual certification of the stockpile is based on the technical evaluations made by the national laboratories and on advice from the three laboratory directors, the Commander of U.S. Strategic Command, and the Nuclear Weapons Council.

• Weapon Refurbishment. Refurbishment extends the viability of nuclear weapons beyond their designed end-of-life date. The national laboratories develop and certify an engineering design for warhead modification through a combination of nonnuclear experiments, flight tests, physics and engineering analyses, and computer simulations. Under the Life Extension Programs, weapons are returned from the field and aging components are refurbished or remanufactured. To assure confidence, changes are minimized, so that refurbished designs are as close as possible to the nuclear-tested designs.

Nuclear Weapons Stockpile Quantities and Deployment

Nuclear stockpile quantities and deployment are determined by Presidential direction. The size and composition of the current U.S. nuclear weapons stockpile have been determined by a number of relevant factors over time. First, the make-up of the stockpile conforms to national security requirements and is a constituent element of the overall U.S. military capability. Second, the number of warheads of each warhead-type in the stockpile is related to the delivery vehicles associated with each weapon.

The 2001 Nuclear Posture Review (NPR) was mandated by Congress in the National Defense Authorization Act for Fiscal Year 2001 (Public Law 106-398). The NPR contains the results of a comprehensive Department of Defense (DoD) review of the U.S. nuclear posture, as well as a long-range plan to sustain and modernize U.S. strategic nuclear forces. The 2001 NPR addressed many issues and reflected significant policy evolution in a number of areas, including the development of the New Triad as a foundation of U.S. national security.

The New Triad provides a mix of strategic offensive and defensive capabilities that include: nuclear and non-nuclear strike capabilities; active and passive defenses; and a robust research, development and industrial infrastructure.

The first leg of the New Triad incorporates conventional capabilities together with the traditional strategic Nuclear Triad, which is composed of Intercontinental Ballistic Missiles (ICBMs), Submarine-Launched Ballistic Missiles (SLBMs) and long-range nuclear-armed bombers. Each leg of the Nuclear Triad provides U.S. leaders with different capabilities. Combined, the three legs of the Nuclear Triad ensure that the U.S. has a variety of survivable nuclear options to support U.S. employment plans. However, the Nuclear Triad has been integrated with non-nuclear strategic capabilities, which strengthen the credibility of U.S. offensive deterrence and form the New Triad.

The second leg of the New Triad therefore requires the development and deployment of active and passive defenses, required to enhance U.S. dissuasion and deterrence against potential adversaries. These defenses include the development of a missile defense system.

The third leg of the New Triad is a responsive infrastructure. Since the end of the Cold War, the U.S. defense infrastructure has been downsized and the nuclear infrastructure has deteriorated. New approaches to the development and procurement of new capabilities are being designed. In addition, the U.S. nuclear infrastructure needs to be repaired to eliminate unneeded weapons and, mitigate the risks of technological surprise. The effectiveness of the New Triad also depends upon Command and Control (C2), intelligence, and adaptive planning. The ability to plan and carry out the rapid and reliable employment of both strike and defense forces provides the United States with a significant advantage in managing crises, deterring attack, and conducting military operations.

In accordance with the Moscow Treaty (see International Treaties) and U.S. national security policy guidance, U.S. nuclear forces will be reduced to between 1,700 and 2,200 operationally-deployed strategic nuclear warheads by 2012. This is a level that will provide a credible deterrent with the lowest possible number of nuclear weapons consistent with national security requirements and Alliance obligations.

The planned reductions will be completed in phases. By 2007, operationally deployed strategic nuclear warheads will be reduced to approximately 3,800. Every other year, there will be an assessment to review the progress in reducing the number of weapons.

To achieve these reductions, the Peacekeeper ICBMs have been retired, the Navy has removed four Trident submarines from strategic service, and the B-1 bomber is now used for conventional weapons only and will not retain its capability to return to a nuclear role.

While operationally-deployed strategic nuclear forces are being reduced in number, the U.S. will continue to maintain a responsive force to remain prepared for any immediate or unexpected contingencies.

  
Nuclear Weapon Types and Delivery Systems

Most nuclear warheads are designed for use with a specific delivery system, or means of delivering the weapon to the target. The U.S. nuclear arsenal includes: gravity bombs deliverable by Dual Capable Aircraft (DCA) and long-range bombers; Tomahawk Land Attack Cruise Missiles/Nuclear (TLAM/N), deliverable by attack submarines (SSN); Air-Launched Cruise Missiles (ALCMs) deliverable by long-range bombers; Submarine-Launched Ballistic Missiles (SLBM); and Intercontinental Ballistic Missiles (ICBM). The United States has developed many warhead-types since the Manhattan Project. Historically, warhead-types entered the stockpile for a limited time and were then retired or replaced by more modern designs.

Gravity bombs are designed to be dropped from planes and must be able to withstand vibrations and changes in air temperature, as well as pressure during the course of a flight. These weapons are designated with the letter "B" followed by the number of the physics package they contain, such as the B61 family of bombs. Gravity bombs are designed to be delivered by the U.S. bomber force composed of the B-52 "Stratofortress" and the B-2 "Spirit". The B-52s are long-range bombers capable of flying at subsonic speeds at altitudes of up to 50,000 feet. The B-52 can carry both nuclear and conventional weapons. The B-2 is also a multi-role bomber capable of delivering both conventional and nuclear munitions. Its low observability or "stealth" characteristics allow it to penetrate enemy defenses. In addition to the strategic nuclear forces, the U.S. has nuclear bombers consisting of F-15E and F-16 Dual-Capable Aircraft (DCA) that can deliver conventional or tactical nuclear bombs in the B61 family. These forces are maintained both in the continental U.S. (CONUS) and in Europe.


Ballistic missiles are guided during powered flight and then release their payloads, which are then subject only to gravity and atmospheric drag. ICBMs are ground-launched ballistic missiles capable of traveling long distances and penetrating heavily defended areas. They can be launched and on-target in minimal time and carry multiple warheads. U.S. ICBM forces currently consist of the Minuteman III missile.




Ohio-class/Trident ballistic missile submarines (SSBNs) provide the sea-based leg of the U.S. nuclear triad. Submarine Launched Ballistic Missiles (SLBMs) are launched from either submerged or surfaced SSBNs. The long range of the missiles and the ability of SSBNs to hide in the ocean make this the most survivable leg of the nuclear deterrent. Each U.S. SSBN is capable of carrying 24 Trident missiles with up to eight warheads per missile.

A cruise missile is powered by a jet engine and flies at low altitudes using an internal automated guidance system to make it more difficult to detect. In comparison to ballistic missiles, cruise missiles have less range and smaller payloads. Cruise missiles can be launched from naval attack submarines or from bombers. The Tomahawk Land Attack Cruise Missile/Nuclear (TLAM/N) is capable of being launched from select SSNs, although they are currently in regeneration status. Additionally, the Air-Launched Cruise Missile (ALCM) and the Advanced Cruise Missile (ACM) are launched from B-52s.