The U.S. Air Force completed a series of stockpile flight tests in August 2025 that paired the F-35 Lightning II with inert B61-12 gravity bombs, confirming the stealth fighter’s readiness for a nuclear strike role. The successful drops at Nevada’s Tonopah Test Range, combined with the United Kingdom’s stated plans to purchase F-35A variants and participate in NATO’s nuclear sharing mission, signal a structural shift in how the Western alliance organizes its deterrent forces. Together, these developments tighten the link between fifth-generation stealth aircraft and the alliance’s forward-deployed nuclear weapons, with direct consequences for burden-sharing and defense spending across Europe.
August Flight Tests Validate F-35 Nuclear Delivery
Between August 19 and 21, 2025, an F-35 carried and dropped inert B61-12 joint test assemblies at Tonopah Test Range in Nevada. The tests confirmed both the weapon’s performance and its reliability when paired with the stealth fighter, according to Sandia reporting, the federal lab responsible for the bomb’s engineering oversight. One detail stands out: the tests included the first-ever thermal preconditioning of a joint test assembly for carriage on an F-35 prior to release. Thermal preconditioning simulates the heat environment a weapon would experience while attached to the aircraft during sustained flight, a step that validates the bomb’s electronics and fuzing under realistic operational stress. Passing that hurdle means the weapon can be trusted to function correctly after hours of high-altitude carriage inside a stealth fighter’s internal weapons bay.
These were not the first compatibility tests between the B61-12 and the F-35. Years earlier, during COVID-era restrictions, Sandia engineers provided virtual support for Captive Carry Flight Test No. 6, in which an F-35 carried a B61-12 compatibility test unit without releasing it. That earlier test established baseline data on how the weapon behaved while attached to the jet. The August 2025 drops built on that foundation by adding the release and free-fall phases, closing the gap between captive-carry validation and full delivery certification. The progression from remote-supported captive flights to live-release stockpile tests reflects a deliberate, multi-year integration timeline rather than a rushed response to any single geopolitical trigger.
B61-12 Enters Sustainment After Production Wraps
The flight tests arrived at a natural inflection point for the B61-12 program itself. Production of the last unit was completed in 2024, formally shifting the program from manufacturing to stockpile sustainment. That transition means the focus now falls on surveillance flight tests, laboratory examinations, and periodic disassembly of weapons at the Pantex Plant in Texas. Data from those activities feed annual assessment reports that the U.S. government uses to certify the safety and reliability of the warhead without conducting underground nuclear detonations. For NATO allies that host or might eventually host B61-12s, this sustainment regime is the mechanism that keeps the weapon credible decade after decade.
The practical effect for deterrence planning is significant. A nuclear gravity bomb is only as useful as the delivery platform that can survive contested airspace long enough to employ it. Older NATO dual-capable aircraft, such as certain F-16 variants and the Panavia Tornado, lack the radar-evading profile of the F-35. Confirming that the B61-12 works reliably when dropped from a stealth jet raises the survivability calculus for any adversary trying to defend against a NATO nuclear strike. It also shifts the cost equation: allies that already operate or plan to buy the F-35 can now, in principle, assume a nuclear delivery role without procuring a separate weapons system. That dual-use logic is central to the broader changes taking shape across the alliance.
UK Plans to Buy F-35As and Join Nuclear Sharing
The United Kingdom has signaled its intention to purchase F-35A variants and join NATO’s nuclear sharing arrangements, a move framed as part of a broader effort to strengthen national security and deliver what official records describe as a defence dividend. The UK already operates the F-35B, the short-takeoff and vertical-landing version used aboard the Royal Navy’s Queen Elizabeth-class carriers. Adding the conventional-takeoff F-35A would give the Royal Air Force a land-based stealth platform compatible with the B61-12, aligning British capabilities with the nuclear sharing framework that currently involves Belgium, Germany, Italy, the Netherlands, and Turkey. In practical terms, that would mean British pilots training under NATO standards for nuclear delivery and British bases potentially adapting infrastructure to store U.S.-owned weapons under joint arrangements.
If London follows through, it would mark the first expansion of NATO’s nuclear sharing circle in decades and the first time a country with its own independent nuclear deterrent, the Trident submarine-launched ballistic missile system, also participates in the alliance’s tactical nuclear mission. That overlap raises questions about cost and strategic logic. Maintaining both a sea-based strategic deterrent and a forward-deployed tactical capability is expensive, and critics will ask whether the duplication adds meaningful security or simply spreads budgets thinner. Supporters counter that dual participation deepens alliance cohesion and gives NATO planners more options for signaling resolve during a crisis, especially along the alliance’s eastern flank. The UK government’s framing ties the decision explicitly to stepped-up national security priorities, suggesting the political calculus favors visible commitment over fiscal caution.
What F-35 Nuclear Integration Means for Alliance Burden-Sharing
Most analysis of NATO deterrence treats the nuclear mission as a static arrangement: a handful of European allies store American bombs and train to deliver them, while the United States provides the warheads and strategic umbrella. The F-35’s validated nuclear role disrupts that assumption. Because more than a dozen NATO members either fly or have ordered the F-35, the pool of potential dual-capable aircraft is far larger than the legacy fleets that previously carried the mission. As integration work progresses, alliance planners will be able to distribute nuclear responsibilities more widely, or at least create the option to do so, without negotiating entirely new basing agreements. The August 2025 tests at Tonopah, overseen by Sandia National Laboratories, effectively remove a key technical barrier to that broader distribution by demonstrating that the B61-12 functions as intended when paired with the stealth jet.
This shift has direct implications for burden-sharing debates that have long plagued NATO politics. Countries investing heavily in the F-35 can now argue that their procurement decisions contribute not only to conventional airpower but also to the nuclear mission, even if they do not immediately host weapons. Conversely, states that continue to rely on older aircraft may face pressure to modernize or accept a diminished role in alliance nuclear planning. The existence of a common, modern platform also simplifies training, certification, and logistics across national air forces. Over time, this could enable rotational nuclear exercises that involve a wider set of allies, spreading both the political symbolism and the operational workload of deterrence more evenly across the alliance.
Managing Risk, Transparency, and Future Upgrades
While the technical milestones are clear, the political management of a more flexible nuclear force will be complex. Allies that do not currently host nuclear weapons may be wary of any future suggestion that they accept storage sites or nuclear-certified squadrons on their soil, even if they operate F-35s. Domestic publics often view nuclear basing arrangements differently from conventional deployments, and governments will have to balance alliance expectations with local sensitivities. At the same time, NATO’s nuclear posture is likely to attract scrutiny from adversaries, who may portray the integration of advanced stealth aircraft and modernized gravity bombs as an escalation. Managing that narrative will require careful public messaging and, where appropriate, transparency about safety, command-and-control, and the defensive nature of the deterrent.
On the technical side, the move from production to sustainment for the B61-12 means that future improvements will focus on reliability, safety, and integration rather than major design changes. Regular surveillance testing, including additional stockpile flight tests similar to those described in Sandia releases, will underpin confidence in the weapon over its service life. The F-35, for its part, will continue to receive software and hardware upgrades that could refine how it carries and employs the bomb, but those changes will have to be carefully validated to ensure they do not introduce new risks. The partnership between the Air Force, the nuclear weapons complex, and allied air forces will therefore remain an ongoing, iterative process, not a one-time certification event. As that process unfolds, it will shape not only NATO’s nuclear posture but also broader debates over modernization, arms control, and the future of deterrence in an increasingly contested security environment.
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*This article was researched with the help of AI, with human editors creating the final content.
