US accelerates development of new B61-13 nuclear gravity bomb to expand strategic attack options.

As reported by the Sandia National Laboratories on April 2, 2025, the United States has shortened the production schedule of its upcoming nuclear gravity bomb, the B61-13, by more than 25 percent. The program now projects delivery of the first production unit seven months earlier than originally expected. This adjustment reflects a response to a stated urgent national security requirement. The B61-13 development effort involves collaboration between Sandia, the Los Alamos National Laboratory, the U.S. Air Force, and the National Nuclear Security Administration (NNSA). It includes modified qualification schedules and integrated planning across agencies to meet revised production goals.
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The B61-13 features a maximum yield of 360 kilotons and includes a guided tail kit for increased accuracy, allowing the bomb to be deployed at standoff distances and to deliver higher yield with improved precision. (Picture source: Sandia National Laboratories)

The B61-13 follows the B61-12 Life Extension Program (LEP), which was completed in December 2023 at an estimated cost of $9 billion. The LEP extended the service life of earlier B61 variants by integrating updated components and safety features, along with a new tail kit for guided delivery. The B61-12 includes a selectable yield of 0.3, 1.5, 10, or 50 kilotons and is compatible with both strategic and tactical aircraft, including the F-35A. Production of the B61-12 is planned to reach approximately 480 units by 2025. The LEP replaced B61-3, B61-4, and B61-7 in the U.S. stockpile and allows for their gradual phaseout. According to the U.S. Department of Defense, the B61-12 is designed to increase delivery accuracy while reducing reliance on higher-yield bombs.

Sandia National Laboratories, the primary site overseeing the B61-13 project, is one of three national research laboratories under the U.S. Department of Energy’s NNSA. Sandia was formally established in 1949, though its origin lies in the “Z” Division of the Manhattan Project, formed in 1945 to support nuclear weapons development at Kirtland Field in Albuquerque, New Mexico. Today, Sandia operates across multiple sites, including Albuquerque, New Mexico; Livermore, California; and test facilities in Kauai, Hawaii. The lab is operated by National Technology and Engineering Solutions of Sandia, a subsidiary of Honeywell International. Its mission spans a wide range of national security areas, including nuclear deterrence, supercomputing, materials science, and energy systems. Sandia employs over 11,500 staff and houses facilities such as the Z Machine, used for high-energy physics and materials testing under extreme conditions.

Nuclear gravity bombs are air-delivered munitions that lack propulsion systems. They rely on free-fall or guided trajectories after release from an aircraft. These weapons are designed to detonate either in the air or upon impact with the ground, with various fuzing and delivery options available. While older variants used parachutes to slow descent, newer designs, such as the B61-12 and B61-13, use guided tail kits for increased precision. These bombs feature variable-yield warheads, allowing operators to adjust explosive output based on mission requirements. The yield of the B61-13, for example, is 360 kilotons, roughly 24 times the explosive power of the 15-kiloton bomb detonated over Hiroshima. When used at full yield, a gravity bomb of this type would cause destruction over several kilometers and produce significant thermal and radiological effects.

The yield of the B61-13, for example, is 360 kilotons, roughly 24 times the explosive power of the 15-kiloton bomb detonated over Hiroshima. (Picture source: US Army)

The United States produces nuclear gravity bombs through its Department of Energy infrastructure, primarily at the Pantex Plant in Texas. Production cycles are controlled and paced according to modernization strategies, safety standards, and arms control agreements. The B61-12 production run is expected to reach 480 units. For the B61-13, the U.S. government has stated that production will not result in an increase in the overall number of nuclear gravity bombs. Instead, each B61-13 produced will reduce the number of B61-12 units by the same amount. According to the Federation of American Scientists, the projected number of B61-13 bombs may be limited to a few dozen. Production timelines indicate that these units could be assembled at the end of the B61-12 schedule, around or after 2025.

The B61 program began in 1962 when the U.S. Department of Defense authorized the development of a lightweight nuclear bomb capable of serving both tactical and strategic roles. Production began in 1968 after testing and engineering design were completed. The weapon was intended to modernize and consolidate earlier bomb types, including the B28 and B43. Developed at Los Alamos National Laboratory, the early B61 variants featured multiple fuzing modes, supersonic survivability, and variable yields. The weapon’s development involved extensive testing under the Atomic Energy Commission, and its earliest production variant, the B61-0, entered service in the late 1960s. Since then, the B61 has remained a central component of U.S. air-delivered nuclear capabilities.

The B61 is approximately 3.6 meters in length, 33–34 centimeters in diameter, and weighs between 320 and 540 kilograms depending on variant and configuration. The design uses a two-stage thermonuclear implosion system. The weapon includes variable yield settings, full fuzing options (airburst, groundburst, laydown), and safety devices such as permissive action links (PALs). Later versions, including the B61-12, incorporate a tail kit and inertial navigation system (INS) for improved accuracy. The weapon’s construction includes safety mechanisms to prevent unauthorized use or accidental detonation, including command disable systems that physically disable internal firing circuits if needed.

Production of the B61-12 is planned to reach approximately 480 units by 2025, and its Life Extension Program (LEP) replaced B61-3, B61-4, and B61-7 in the U.S. stockpile, allowing for their gradual phaseout. (Picture source: Sandia National Laboratories)

There are thirteen major modifications of the B61 (Mods 0–13). Of these, five are currently active or maintained in limited stockpile status. The B61-3 and B61-4 are lower-yield tactical bombs; the B61-7 is a high-yield strategic variant; the B61-11 is an earth-penetrating version designed for hardened underground targets; and the B61-12 is the newest precision-guided modification under mass production. Each variant has included changes in safety systems, delivery platforms, or physical configuration. The B61-13, announced in 2023, incorporates the high-yield warhead of the B61-7 and the guidance and safety features of the B61-12. According to the Department of Defense, this new variant is intended to offer strike options against targets that require a combination of yield and accuracy not provided by existing lower-yield bombs. The development of the B61-13 has been presented as a replacement for some existing B61-7 units and as a pathway toward retiring the B83-1, a legacy bomb with a yield of 1.2 megatons.

The B61-13 features a maximum yield of 360 kilotons and includes a guided tail kit for increased accuracy. This allows the bomb to be deployed at standoff distances and to deliver higher yield with improved precision. Though not designed as a deep-penetration weapon, the B61-13 is expected to be capable of damaging hardened targets through ground-shock effects, depending on yield and detonation mode. Compared to the 50-kiloton B61-12, the B61-13 offers greater destructive potential. A 360-kiloton surface burst would generate a large blast radius, substantial thermal effects, and fallout, depending on the environment and altitude of detonation. Defense officials have stated that the bomb’s primary use is to provide the president with additional options in scenarios requiring high-yield precision.

B61 bombs have been integrated across a range of delivery platforms. These include strategic bombers such as the B-52 Stratofortress, B-1B Lancer (no longer nuclear-certified), B-2 Spirit, and the upcoming B-21 Raider. Tactical aircraft certified to carry B61 variants include the F-15E Strike Eagle and F-16 Fighting Falcon. In 2023, the F-35A became the first fifth-generation stealth fighter to be certified for nuclear delivery with the B61-12. NATO countries operating dual-capable aircraft under nuclear sharing arrangements, such as Germany, Italy, Belgium, the Netherlands, and Türkiye, host U.S. B61 bombs for potential use in conflict. Although the B61-13 is physically compatible with these aircraft, current U.S. policy restricts its deployment to strategic bombers, with no plans to equip the F-35A or other fighters, such as the Panavia Tornado, with this variant.