With the completion of the B61-12 program, work has now started on the B61-13, specifically designed for “certain harder and large-area military targets” in support of the Nuclear Posture Review’s need to defeat “hard and deeply buried targets.”
Sandia National Laboratories has started to work on the B61-13 nuclear bomb program, as shown in an image of the weapon’s first joint test assembly released on its website on Mar. 19, 2025. While it is not clear when the development took place, it is consistent with earlier reports about the NNSA (National Nuclear Security Administration) announcing the beginning of the B61-13’s development, following the manufacture of the B61-12’s LPU (Last Production Unit) in Dec. 2024, and the announcement of the program’s conclusion on Feb. 20, 2025.
SNL described the picture saying that an engineer is making “connections on the first B61-13 joint test assembly,” referring to the orange-colored unit on the trolley. The weapon appears similar in shape and dimensions to the B61-12, and any differences, if any, are not discernable.
Joint test assembly units are not live weapons and they do not have the nuclear warhead, but they have the rest of the internal components. These serve multiple functions, such as governing the bomb’s separation from the aircraft, interfacing with the aircraft’s systems, moving the control surfaces in accord with the guidance section, and the arming mechanism. It is unclear, however, if the pilot can select the yield and type of explosive mode – air burst or burst on impact – or if they need to be set on the ground.
B61-13 program begins
An engineer makes connections on the first B61-13 joint test assembly.
Source: Sandia pic.twitter.com/1phlnOQlBU
— Casillic (@Casillic) March 20, 2025
The development of the B61-13 was first announced in 2023. An Oct. 2024 report from the NNSA said that the First Production Unit (FPU) of the B61-13 is scheduled for FY 2026, with completion planned for FY2028. SNL is the design, engineering and systems integration laboratory for the non-nuclear components in both the B61-13 and the B61-12’s LEP (Life Extension Program), which, as mentioned earlier, has concluded.
Project ahead of schedule
According to SNL’s short description accompanying the image, the B61-13 project is in response to a “critical challenge and urgent need,” where the development adopted “innovative program planning that resulted in projected delivery seven months earlier than expected.” This is “more than 25% decrease in overall time to (the) first production unit,” added SNL.
“The B61-13 team reprioritized qualification activities, planned tests with the U.S. Air Force stakeholders and jointly completed requirements with Los Alamos National Laboratory and NNSA. Their creativity in system qualification put an aggressive set of plans in motion to meet stakeholder expectations,” the release said.
B61-13 bomb
According to an Oct. 2023 fact sheet on the B61-13 from the DoD (Department of Defense), the B61-13 is specifically designed to “strengthen deterrence of adversaries and assurance of allies and partners by providing the President with additional options against certain harder and large-area military targets.”
Additionally, as directed by the Nuclear Posture Review (NPR), the DoD “will separately continue its work to complete and implement a comprehensive strategy for defeat of hard and deeply buried targets.” The B61-13 actually would “replace some of the B61-7s the current stockpile,” as well as having a similar yield, “which is higher than that of the B61-12.”
The FAS (Federation of American Scientists), perusing public DoD and Pentagon material, said that the B61-13 uses the B61-7’s 360 kiloton warhead, but with the addition of “new safety and use-control features” and a guided tail kit. The tail kit will enhance the B61-13 “limited earth penetration capabilities,” with the FAS specifying “through soft soil.”
This will enable the weapon to strike underground targets with “yields equivalent to a surface-burst weapon of more than one megaton.” The B61-13 will reportedly have both lower and higher yield options, from 0.3 to 1.5 kt, and between 10 to 50 kt.
Like the B61-12, the B61-13 will see grueling stress, shock, pressure, impact and environmental tolerance testing to assess that the bomb as whole, along with its individual parts, will function as planned under a variety of conditions during operational use. These include being fired from a Davis Gun operated by SNL into an 8 feet deep pool, a Forward Ballistic Impact test on a high-speed rail-mounted track and, finally, tests from various aircraft.
B61-12 gravity nuclear bomb
In the B61-12’s LEP, SNL produced several components to be delivered to the Kansas City National Security Campus and Pantex Plant for full-scale production. The B61, a nuclear gravity bomb deployed by the U.S. Air Force and North Atlantic Treaty Organization (NATO) forces, has been in service since 1968.
The B61-12 is meant to replace most older modifications of the B61, including the B61-3, B61-4, B61-7 and B61-11, and have an extended service life of at least 20 years. The B61-12’s LEP addressed obsolescence issues in the components and parts of the B61 stockpile, including encryption algorithms, safety and use control features, while supporting compatibility with future aircraft designs. The production began nearly three years ago and the LEP reported cost was around $9 billion.
Thus, the B61-12 is not exactly a new weapon, because it merely puts the warheads from the older B61-4 (that started production in 1979) inside a new body, which itself contains advanced guidance, INS (Inertial Navigation System), electronics, a tail assembly by Boeing and two spin-rocket motors. It has a host of reused, “redesigned” and “remanufactured” components like the Spin Rocket Motor, actuators, pulse battery assemblies, impact sensors, patch antennas, gas transfer system, power supplies, thermal batteries and casings.
This is an important one. B61-13 is designed to replace aging B61-7 while seriously bumping up the yield. 61-7 is around 340kt. Rumors are this unit yields 1/2 MT. Basically, it’s a military base killer. It’s also specifically designed to be carried by F-35 and B-21 Raider.… https://t.co/45OHtpLICR pic.twitter.com/pa7cmVE8i6
— 🌡Mercury 🇺🇸 (@RealestMercury) March 21, 2025
Based on the 2022 NPR, beside other nuclear treaties and stockpile limitation agreements, the B61-13 will not increase the overall number of weapons in the U.S. stockpile, since it will use already existing warheads. In other words, the number of B61-12s produced will be lowered by the same amount as the number of B61-13s produced.
User aircraft
While the B61-12 has been certified to be operated by the F-15E Strike Eagle, F-35A Lightning II, the B-2 Spirit stealth bomber, the F-16 Fighting Falcon, the German (Luftwaffe) and Italian Air Force’s (Aeronautica Militare) Panavia Tornados, and the U.S. Air Force’s incoming B-21 Raider stealth bomber, the new B61-13 is however meant to be used by the Raider only.
Therefore, we can expect the B61-13’s future development being aligned with the initial Low Rate Initial Production lots of the B-21 Raider. There is no information yet on the Raider’s payload configuration, except for the doors seen between its landing gear doors in bottom view shots during its test flights from the Air Force’s Plant 42 at Palmdale in California.
W80-4 warhead and missile integration
Technologists prepare a W80-4 Joint Test Assembly test unit for transportation.
Source: Sandia pic.twitter.com/g1rHTRFOy2
— Casillic (@Casillic) March 20, 2025
It is also possible the B61-13 may be initially used by the B-2 Spirit, until the B-21 Raider is fully online and replaces the former. Because it is also meant to be deployed only by bombers, the B61-13 would be stored only within the United States. At the same time, because the B61-13 uses the same mechanical and electronic interface as the B61-12, the fighters certified to operate the B61-12 could also use the B61-13 in future, should the plans change.
