> "The most recent operational variant, the B61-11, entered service in 1997 and is the first to dramatically differ in form, as well as function. The U.S. military treats this version as a combination tactical and strategic bomb even though it’s based on the B61-7 and reportedly has a single, maximum yield of approximately 340-400 kilotons."
> "The bigger difference, though, is that it has a significantly reinforced shell, possibly with a depleted uranium penetrating nose section, a delay fuzing system, and a booster rocket motor in the rear, all so it can break into deeply buried, hardened facilities. There are less than 100 of these bombs in existence, according to publicly available data, and the United States more or less built them with one specific target in mind."
> "In 1996, Russia finished work on its Kosvinsky Kamen bunker, part its so-called “continuity of government” plans to protect senior leadership in the event of a nuclear strike or other major emergency. Similar in concept and reportedly similarly—if not better—protected than the U.S. military’s Cheyenne Mountain Complex or Site R, also known Raven Rock, the Kremlin built it specifically to be hardened against nuclear weapons going off up above. The B61-11’s job was to put even those defenses beyond reach in what would likely already be an apocalyptic scenario."
> "Before the B61-11, the United States planned to use a much less elegant approach when it came to nuclear bunker busting, relying on aging B53 bombs, a design dating back to 1958 for this purpose. These 12-foot long, 4-foot wide, nearly 9,000 pound weapons would have used the sheer explosive power of their 9 megaton yield to create massive craters and crush underground targets. The U.S. government also explored using a modified B83-1, with its 1.2 megaton yield, for the role before deciding on the modified B61."
(The article also discusses the newer B61-12 as a potential substitute, although it's unclear as the key information is secret).
"Get To Know America’s Long Serving B61 Family Of Nuclear Bombs" (2019)
https://www.twz.com/19263/get-to-know-americas-long-serving-...
> "The most recent operational variant, the B61-11, entered service in 1997 and is the first to dramatically differ in form, as well as function. The U.S. military treats this version as a combination tactical and strategic bomb even though it’s based on the B61-7 and reportedly has a single, maximum yield of approximately 340-400 kilotons."
> "The bigger difference, though, is that it has a significantly reinforced shell, possibly with a depleted uranium penetrating nose section, a delay fuzing system, and a booster rocket motor in the rear, all so it can break into deeply buried, hardened facilities. There are less than 100 of these bombs in existence, according to publicly available data, and the United States more or less built them with one specific target in mind."
> "In 1996, Russia finished work on its Kosvinsky Kamen bunker, part its so-called “continuity of government” plans to protect senior leadership in the event of a nuclear strike or other major emergency. Similar in concept and reportedly similarly—if not better—protected than the U.S. military’s Cheyenne Mountain Complex or Site R, also known Raven Rock, the Kremlin built it specifically to be hardened against nuclear weapons going off up above. The B61-11’s job was to put even those defenses beyond reach in what would likely already be an apocalyptic scenario."
> "Before the B61-11, the United States planned to use a much less elegant approach when it came to nuclear bunker busting, relying on aging B53 bombs, a design dating back to 1958 for this purpose. These 12-foot long, 4-foot wide, nearly 9,000 pound weapons would have used the sheer explosive power of their 9 megaton yield to create massive craters and crush underground targets. The U.S. government also explored using a modified B83-1, with its 1.2 megaton yield, for the role before deciding on the modified B61."
(The article also discusses the newer B61-12 as a potential substitute, although it's unclear as the key information is secret).