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What is the Smallest Nuclear Weapon?

Michael Anissimov
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Updated: May 21, 2024
Views: 14,590
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The smallest nuclear weapon known to the public was the W54, a 10.6"x15.7" (27.3 x 40 cm) cylinder that only weighed 51 lbs (23 kg). The W54 was used in both the Davy Crockett recoilless rifle (a nuclear mortar for ground troops) and the Mk-54 SADM (Special Atomic Demolition Munition), a hand-delivered nuclear time-bomb for attacking enemy ports. The prototype for the W54, tested during Operation Hardtack in 1954, was even smaller, at just 10.6"x11.8" (27 x 30 cm), close to what many nuclear scientists think is the theoretically smallest nuclear weapon. The Davy Crockett had a 10-20 ton yield — intentionally kept low to be safe to those firing it — while the SADM had a variable yield between 10 tons and 1 kiloton.

To create a nuclear weapon requires a critical mass of a fissile material, and a chassis for a gun-type trigger or explosive lenses. A critical mass of plutonium is about 10.5 kg (23 lb), 10.1 cm (4 in) across. This is not enough to start a multiplicative chain reaction, but does produce enough radiation to be deadly if you were holding it.

To produce a chain reaction requires upping the plutonium, just a bit — just 10% over critical mass is sufficient to create a nuclear weapon with a yield of 10-20 tons, already in the range of the Davy Crockett warhead. 20% over critical mass gives a yield of 100 tons, while 35% over critical mass can reach 250 tons. The smallest nuclear weapons would have a yield somewhere in this range.

The public can't know for sure what the smallest nuclear weapon is, because it is probably classified. The Soviet Union worked on a variety of nuclear weapons that remain completely secret, and the US has as well, although there is more transparency in the latter case. One former Soviet general, Alexander Lebed, claimed the existence of "suitcase nukes" on a news interview in September 1997, setting off a chain of speculation about whether the smallest nuclear weapon might fit in a 60 x 40 x 20 cm suitcase. The general consensus is that this would be enough room to create a nuclear weapon, especially for a technologically sophisticated country. However, there is little concrete evidence for it.

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Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
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Discussion Comments
By croydon — On Oct 28, 2014

@pleonasm - I don't know a lot about the politics that surrounded the cold war or how countries have dealt with it since, but from what I do know, there were massive amounts of nuclear weapons stockpiled during that time in different places and they have not all been dismantled. I don't know how possible or impossible it is to create a miniature nuclear weapon from a large one, but it doesn't seem on the surface of it, to be completely out of the question.

That's what should worry people, because there is no way that every single nuclear weapon currently in the world is being completely protected every second in a way that could prevent it from being stolen.

I just hope no crazy or bloodthirsty nuclear terrorists ever come up with a viable idea of trying to co-opt the weapons that already exist to carry out an attack.

By pleonasm — On Oct 28, 2014

@MrsPramm - Nuclear weapons aren't common even now, when the technology isn't that difficult to figure out, because they are so tough to make. It's not something that a small country could accomplish by themselves, which is one reason no one believes North Korea has managed to do it.

It takes a massive amount of resources to make them and I doubt that any terrorist organization would be able to put that together. That's not to say that a nuclear attack with a suitcase nuke isn't possible, but I thankfully I don't think it's probable.

By MrsPramm — On Oct 27, 2014

The idea of suitcase nukes really scares me. While the threat of nuclear war is bad, of course, countries are generally not going to get to the point where the best option is to use nuclear weapons, because they are so afraid of retaliation.

But if you have a smaller nuclear weapon in the hands of a terrorist, they will feel no such restrictions because often what they want is for chaos to reign and people to die and they don't have a permanent residence that can be destroyed by retaliation.

The smaller a nuclear weapon becomes, the easier it is to transport and sell and the more likely it becomes that someone will get their hands on it that is willing to use it, whatever the cost. This threat alone seems like a good reason for countries to ensure they never develop this technology.

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Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
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