We don’t know if this is actually deployed yet.

Russia’s Poseidon (otherwise known as Status-6 Oceanic Multipurpose System) is a nuclear powered nuclear weapon that goes over 70 miles an hour under water. It is 80 feet long and weighs over 100 tons.

It has almost unlimited range and so could reach its target from almost anywhere, albeit slowly.

And it would be tremendously difficult to stop.

Clever those Russkies…