But Russia's Poseidon reportedly uses a warhead hundreds of times stronger, and perhaps even as strong as the largest bomb ever detonated. Additionally, it will come into direct contact with water, marine animals, and the ocean floor, kicking up a radioactive tsunami that could spread deadly radiation over hundreds of thousands of miles of land and sea, rendering it uninhabitable for decades.
In short, while most nuclear weapons can end a city, Russia's Poseidon can end a continent.
Even in the mania at the height of the Cold War, nobody took seriously the idea of building such a world-ender, Malcolm Davis, a senior analyst at the Australian Strategic Policy Institute told Business Insider.
Davis calls the Poseidon a "third strike vengeance weapon," meaning that Russia would attack a NATO member, the US would respond, and a then devastated Russia would flip the switch on a hidden nuke that would lay waste to an entire US seaboard.
According to Davis, the Poseidon would give Russia a "coercive power" to discourage a NATO response to a Russian first strike.
Russia here would not only seek to re-occupy Eastern Europe, "but coerce NATO to not act upon an Article V declaration, and thus lose credibility. [Russian President Vladimir] Putin has made it clear he seeks the collapse of NATO. If NATO doesnt come to the aid of a member state, it's pretty much finished as a defence alliance," he continued.
Essentially, Russia could use the Poseidon as an insurance policy while it picks apart NATO. The US, for fear that its coastlines could become irradiated for decades by a stealthy underwater torpedo it has no defenses against, may seriously question how badly it needs to save Estonia from Moscow's clutches.
"Putin may calculate that NATO will blink first rather than risk escalation to a nuclear exchange. Poseidon accentuates the risks to NATO in responding to any Russian threat greatly, dramatically increasing Russias coercive power," Davis continued.
Davis also suggested the Poseidon would make a capable but heavy-handed naval weapon, which he said could likely take out an entire carrier strike group in one shot.
Russias new nuclear ferocity
Recently, Russia has signaled its willingness to use nuclear weapons to coerce the West with its violation of the Intermediate Nuclear Forces treaty, said Davis. These missiles are purpose-built for taking out European capitals from the Russian mainland.
But Russia has frequently engaged in nuclear saber-rattling when it feels encircled by NATO forces, and so far has steered clear of confronting NATO with kinetic forces.
"Whether that will involve actual use or just the threat of use, is the uncertainty," said Davis.
While it's hard to imagine a good reason for laying the kind of destruction the Poseidon promises, Davis warned that we shouldn't assume the Russians think about nuclear warfare the same way the US does.