On October 27 the U.S. Military announced plans to develop a new class of nuclear gravity bomb, the B61-13, which Pentagon has advocated the development of on the basis that the B61-12 bombs currently being acquired have an insufficient payload to engage some of the hardened underground or wide area targets that could be encountered. Modern variants of the B61 allow operators to set their explosive force before use, with the B61-12’s highest setting of just 50 kilotons, although around triple the 15 kilotons used to destroy Hiroshima in 1945, still being orders of magnitude smaller than many of the larger nuclear bombs in service. The highest setting for the older B61-7 variant of around 350 kilotons by contrast is one of the highest yields ever integrated onto a fighter sized aircraft, with the B61-13 expected to have a similar yield and thus provide a more suitable replacement for B61-7s in the arsenal. A Pentagon report summarised that the new bomb would “provide the President with additional options against certain harder and large-area military targets.”
“The B61-13 would take advantage of the current, established production capabilities supporting the B61-12, and would include the modern safety, security, and accuracy features of the B61-12,” a Pentagon press report explained. It elaborated: “The B61-13 would be deliverable by modern aircraft, strengthening deterrence of adversaries and assurance of allies and partners by providing the President with additional options against certain harder and large-area military targets. It would replace some of the B61-7s in the current nuclear stockpile and have a yield similar to the B61-7, which is higher than that of the B61-12.” B61s are expected to be most widely deployed by F-35 fifth generation fighters, which is the only Western stealth fighter class capable of deploying nuclear warheads. As F-35s increasingly form the backbone of the U.S. Air Force, and a growing number of allied fleets, a greater ability to conduct nuclear strikes against hardened or wide area targets has significant global strategic implications. The U.S. currently has nuclear sharing agreements with five European states, four of which are F-35 clients, while there have been indications that Poland and Japan which have also ordered the stealth fighters could also come under agreements to provide wartime access to American nuclear bombs. Although it has been reported that the B61-13 will not come under nuclear sharing agreements, this remains uncertain and could change should proliferating a higher payload strike capability be perceived to be in the alliance’s interest.
The importance of the ability to penetrate fortifications has risen as tensions between the United States and its leading adversaries has risen, with China, North Korea, Russia and Iran all having heavily fortified key military facilities deep underground. North Korea in particular has been a leader in proliferating these technologies and provided hardening for Iranian and Hezbollah facilities, with Iran in February having revealed images of a very well fortified airbase – named Eagle 44 – suspected of having been built into a mountain with Korean support. Airfields, arms production faculties, weapons caches, civilian shelters and entire bases and barracks have been built deep underground across North Korea often at depths exceeding 100 metres, with the capital Pyongyang’s underground railway system fortified similarly deeply. This has posed a key challenge to American plans for an assault on the country for decades, including in 2017 when the White House came close to authorising an attack using up to 80 nuclear warheads. Although no B61 variant is expected to be able to penetrate such deep sites, the precision guidance of more modern variants allows multiple bombs to be used on the same site to great effect – with a single F-35 squadron potentially able to drop over a dozen in a single sortie. As among the most expensive munitions in the world, famously costing more than their weight in gold, the number of fortified targets will nevertheless exceed the number of B61s available several times over.