Critics and supporters of NATO’s nuclear deterrence posture, which relies partly on forward-deployed U.S. nuclear weapons in Europe, hardly agree on anything. But when it comes to nuclear sharing, their assessments are remarkably similar. Both groups claim, either explicitly or implicitly, that American B-61 gravity bombs and the nuclear sharing arrangement as a whole are militarily obsolete and lack credibility. However, participants in the ongoing debate about the future of NATO’s nuclear deterrence posture have failed to realize that the technological and political nature of nuclear sharing is changing.
The F-35A Lightning II, which is set to replace current legacy fighters in almost all NATO states that take part in nuclear sharing, is a significantly more capable aircraft than the legacy fighters it is replacing. Together with the modernized B61-12 nuclear bomb, it will reconstitute NATO’s regional deterrence capabilities and help to deter further Russian aggression. Furthermore, the procurement of the F-35A by a large number of NATO members — and by Germany in particular — will alleviate doubts about the political credibility of the nuclear sharing commitment.
Because the F-35A will become the foremost fighter jet in Europe and users cannot make any modifications to the airplane, it also offers new opportunities for alliance members in Eastern Europe to send jets and pilots to Western Europe and train for the nuclear sharing mission. As pilots from Eastern Europe, due to their heightened threat perception, may well be more willing to employ nuclear weapons in a potential conflict with Russia, such direct participation would reassure Eastern European allies that the nuclear commitment is politically credible.
If NATO actively pursues this kind of cooperation, the times when nuclear sharing was a defunct relic of the Cold War will soon be over — besides bolstering deterrence, the arrangement would further promote the unity and cohesion of the trans-Atlantic alliance.
The Credibility Issues of Nuclear Sharing
Under NATO’s nuclear sharing arrangement, the United States deploys tactical nuclear weapons in Europe to convince its friends and foes that the commitment to defend Europe is credible. This is because tactical nuclear weapons create an escalatory chain that links the security of the United States with the security of its European allies, a mechanism that is known as coupling. Moreover, forward-deployed tactical nuclear weapons bolster deterrence since their presence near the front lines increases the likelihood of nuclear escalation in a conventional conflict.
Three decades after the Cold War, the United States has withdrawn almost all of its tactical nuclear weapons from Europe. Only a small number of B-61 gravity bombs, designed to be employed against enemy targets using so-called dual-capable aircraft operated by European NATO members, remain on a handful of allied air bases across the continent. According to recent estimates, about 100 bombs are deployed in Italy, Germany, Turkey, Belgium, and the Netherlands.
This stockpile is no longer regarded as credible.
One issue is military-technical. As a popular argument goes, using fourth-generation fighters such as the F-16 or the aging Tornado to penetrate modern Russian air defenses and deliver unguided bombs on Russian territory would represent “seven consecutive miracles.” Not only would the aircraft need to survive an enemy first strike and receive authority from the U.S. president to arm the nuclear bombs, but they would also have to take off successfully, meet up with a tanker aircraft to refill their fuel tanks mid-air, make it to the target without being engaged by enemy air defenses or fighters, find and identify the target, and release the weapon as designed.
The war in Ukraine has further emphasized the problems that any fourth-generation dual-capable aircraft would face in the modern battlespace. By employing modern air defense systems, Russia and Ukraine have mutually denied themselves air superiority, making it nearly impossible for either side to fly close air support missions without sacrificing their own jets. Russian forces have thus resorted to firing ballistic missiles and cruise missiles for strategic air attacks — often from within Russia’s own airspace, far away from Ukrainian surface-to-air missile batteries.
Another issue is political. Especially after the ratification of the Treaty on the Prohibition of Nuclear Weapons in October 2020, a growing number of NATO states debated openly whether to join the treaty and end their participation in NATO’s nuclear sharing arrangement. Germany in particular was on the fence about the future of nuclear sharing, with senior politicians arguing for a withdrawal of the remaining U.S. nuclear warheads. This has sparked questions about the willingness of Western European states to share the risks associated with nuclear deterrence. It has also led to apprehensions in Eastern Europe, where experts and politicians feared that a German exit could deal a major blow to the alliance’s nuclear cohesion and ultimately decrease the credibility of NATO’s security guarantees on the eastern flank. After all, the political dimension of nuclear sharing, which consists of information sharing, consultations, as well as common planning and execution, is often considered even more important than military-technical factors.
NATO has also failed to adapt the nuclear sharing scheme to the different threat perceptions within the alliance, which further undermines the political credibility of the arrangement. Even though the most pressing threat to NATO is in the East, almost every host nation is located in the West. Therefore, it should come as no surprise that Poland has repeatedly requested to host U.S. nuclear weapons.
The Changing Technological Nature of Nuclear Sharing
NATO’s nuclear sharing arrangement may not be credible today, but it likely will be in the near future. With the F-35A scheduled to replace the remaining fourth-generation dual-capable aircraft within the alliance and the B61-12 set to arrive in European storage facilities this year, the strategic outlook today is vastly different than a couple of decades ago.
Even though the F-35A has yet to perform a number of crucial tests to go into full-rate production, is plagued by availability issues due to a lack of spare parts and functional engines, and still has over 800 open deficiencies, it is already a very capable fighter. Thanks to its stealth capabilities, electronic warfare suite, and advanced sensors, which provide the pilots with situational awareness unmatched by any fourth-generation platform, the F-35A will give nuclear sharing participants unprecedented ability to penetrate highly defended Russian airspace.
The advances of stealth capabilities should be obvious to anyone who closely watched the performance of the F-117 Nighthawk during the first night of Operation Desert Storm in 1991. Whereas fourth-generation fighters were employed in large strike packages to ensure adequate protection, the F-117s slipped through Iraqi air defenses and struck their targets unimpeded, without any additional support.
To be sure, stealth alone is no longer sufficient to ensure penetration against advanced integrated air defense systems. Mission planners need to use intelligence, surveillance, and reconnaissance assets to identify holes in enemy air defense coverage and to work out where and when to jam or suppress enemy radars in order to map out flight paths that minimize the risk of radar detection. The F-35A, however, can do a fair bit of this highly complex work on its own. Using its advanced sensor suite, the aircraft is able to quickly geolocate and classify enemy radars, as well as display them to the pilot. These capabilities, which are currently being used on NATO’s eastern flank to gather valuable intelligence, greatly enhance the F-35A’s ability to operate safely in contested airspace, and it’s no coincidence that the F-35A has been highly successful on the international market.
The modernized B61-12, which will be fully integrated into the F-35A Block 4 variant, offers additional operational credibility for the nuclear sharing mission. The traditional B61 can be delivered in four different ways: in free-fall or retarded airburst, as a free-fall surface burst, or in a “laydown” mode where the bomb is released from a low-flying aircraft and slowed down by a parachute (to prevent disintegration) before it detonates by timer. In all of these cases, the bomb behaves as any unguided general-purpose bomb — it is not as accurate as modern precision-guided munitions, and the pilots need to get very close to their targets. The B61-12, however, is outfitted with a new tail kit comprising an inertial guidance system and a GPS receiver, allowing F-35A pilots to deliver their nuclear bombs with much greater accuracy. Reportedly, the bomb comes with a circular error probable of five meters or less as long as GPS data is available — and with a circular error probable of 30 meters if not. This means that half of the nuclear warheads would explode within five or 30 meters of their actual targets, respectively. This is a substantial improvement over the 100-meter accuracy of the older B61 models. The B61-12’s modest standoff range also improves aircraft survivability because it leaves more time for safe aircraft escape after weapon delivery.
Taken together, the F-35A and the B61-12 will result in a significant boost in operational credibility for NATO’s nuclear sharing mission. Of course, this does not mean that it would be easy, nor that success would be guaranteed. Air campaigns are a hugely complex business, and critics of nuclear sharing have rightfully pointed to a number of operational challenges, not least of which is the requirement to refuel NATO’s dual-capable aircraft in contested airspace. But since Russian air defense capabilities are not as effective as publicly suggested and do not create impenetrable bubbles for NATO operations, there is a reasonable chance of success.
Fixing the Politics of Nuclear Sharing
Besides ameliorating the military-technical issues of nuclear sharing, the F-35A can also help to fix the political credibility issues.
The F-35A sends a strong political signal that Western European governments will continue to participate in the nuclear sharing arrangement and are still willing to deliver U.S. nuclear weapons on enemy soil. This is because the jet is tailored for the nuclear delivery mission, unlike any other fighter on the Western market. At the present moment, the F-15E Strike Eagle is the only other modern fighter jet certified for the B61-12, and the Strike Eagle would arguably face major difficulties in penetrating enemy air defenses. Moreover, as both Switzerland and Finland have noted in their procurement decisions, the F-35A promises not only high security of supply, but also the highest development potential of all fighter jets available on the market, ensuring that it will remain relevant in the battlespace until at least 2060. The F-35A therefore signals a long-term political commitment to the nuclear sharing mission — much more so than models such as the F/A-18F Super Hornet, which Germany considered purchasing as a stopgap measure even though its production line is on life support.
The German procurement of the F-35A also matters politically since it solidifies the nuclear character of the alliance and makes efforts to end German participation in NATO’s nuclear sharing arrangement exceedingly unlikely. As long as Germany was still undecided about the successor model for its old Tornado fighter-bombers, lawmakers were presented with a once-in-a-lifetime opportunity to exit the unpopular arrangement. Due to the dismal readiness state of the German Tornado jets, a decision for or against a specific aircraft model, or no decision at all, might have effectively precluded further participation in the nuclear sharing scheme. In addition, a German de facto exit might have motivated other countries to follow suit. Now that the deal is signed and sealed, this opportunity has passed. In a last-ditch effort, critics tried to argue that the F-35A would be a waste of money. But with the military-technological base in place, nuclear sharing critics will have a hard time ending the arrangement because doing so would require an active decision, rather than simple inaction.
Perhaps most importantly, the F-35A offers new ways of cooperation between NATO members that did not previously exist. Once the jet is in service in Poland, the Czech Republic, Finland, and Romania, NATO allies on the eastern flank could deploy airframes and pilots to Western Europe and train jointly to employ U.S. nuclear weapons. Such a program, which is not currently possible because all states operate different aircraft types, would significantly increase the political credibility of NATO’s nuclear sharing arrangement. Due to their diverging threat perceptions, the Polish government and Polish pilots, for example, might well be more willing to employ nuclear weapons than, say, the German government and German pilots.
Usually, even operating the same aircraft type does not guarantee full interoperability, because there are differences between national versions, as the Anglo-German air policing mission in the Baltics exemplifies. That said, for the F-35A, most states will not be allowed to modify the physical or data systems of the airplane. NATO members could thus actively explore such a cooperation, perhaps with Germany being in the lead. As a side effect, deploying additional airframes to Germany would also ease pressure on Germany’s tiny F-35A fleet.
Russia would be unlikely to appreciate such an arrangement, but it is still far less provocative than deploying U.S. nuclear warheads in Eastern Europe. Moreover, as Russia has already announced its intent to station nuclear weapons in Belarus, the benefits of deeper cooperation on nuclear sharing within NATO would likely outweigh any detrimental effects on European security resulting from hypothetical Russian countermeasures.
Making the F-35A the Central Pillar of Regional Deterrence
More than three decades after the Cold War, it is widely accepted that NATO’s nuclear sharing arrangement lacks military-technical and political credibility.
In a quest to resurrect this “magic ingredient” of deterrence, various experts have suggested that the United States should level the playing field and field its own ground-based missiles in Eastern Europe. It is said that such a deployment could address Russia’s overmatch of conventional and nuclear missile systems and close a gap on the escalation ladder after the demise of the Intermediate-Range Nuclear Forces Treaty, which banned surface-to-surface missiles with ranges between 500 and 5,500 kilometers. NATO emphasized in 2021 that it has no intention to deploy nuclear-tipped missile systems in Europe, but Russia’s full-scale invasion of Ukraine in 2022 has lent new urgency to the debate about conventional and even nuclear missiles.
The F-35A Lightning II is likely to resolve the long-standing credibility issues of NATO’s nuclear component once it enters into service with European NATO allies. If NATO seeks to maintain a nuclear posture that relies partly on forward-based nuclear weapons, the alliance should thus continue making the F-35A the central pillar of its deterrence strategy. The F-35A is suitable for a wide set of missions, such as offensive and defense counter-air, cruise missile defense, suppression or destruction of enemy air defenses, reconnaissance, electronic attack, close air support, as well as battlefield interdiction, thus offering considerably more flexibility than ground-based missiles that can only be employed against fixed targets. It also carries a significant political value that goes beyond military capabilities.
Rather than fielding an entire new set of weapon systems in Europe, NATO would be wise to take full advantage of the F-35A’s capabilities and invest in additional weapons and expertise to suppress and defeat Russian air defenses. European F-35A operators could also evaluate whether they can adapt strategies similar to the U.S. Air Force’s Agile Combat Employment concept. “Hot refueling” their fighter jets on the ground, for example, might be a solution to extend the range of operations in contested environments. Finally, NATO members should consider detailing F-35A airframes and pilots from Eastern Europe to air bases in Western Europe to train for the nuclear mission. All of these measures would further increase the credibility of nuclear sharing arrangement and, ultimately, strengthen deterrence.
Frank D. Kuhn works as project coordinator for the Cluster for Natural and Technical Science Arms Control Research at Peace Research Institute Frankfurt. His research interests include nuclear deterrence, arms control and nonproliferation, as well as military technology and strategy. The views expressed in this article represent those of the author alone.
Image: Los Alamos National Laboratory
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