https://en.wikipedia.org/wiki/B61_nuclear_bomb
https://en.wikipedia.org/wiki/Unguided_bomb
https://www.theguardian.com/world/2022/oct/07/biden-putin-nuclear-threats-tactical-strike-us-response-analysis
https://www.politico.com/news/2022/10/26/u-s-plans-upgraded-nukes-europe-00063675
https://www.newsweek.com/what-are-b61-12-gravity-bombs-russia-says-us-lowering-nuclear-weapon-threshold-1755584
https://fas.org/blogs/security/2016/01/b61-12_earth-penetration/