Poseidon underwater drone
Image: Russian Ministry of Defense/east2west news
According to reports, a Russian Navy submarine has left port carrying a Poseidon underwater nuclear drone. The drone is described by official Russian sources as a nuclear-powered drone carrying a 2 megaton nuclear warhead. By virtue of being nuclear powered a Poseidon is expected to have an infinite range. Its maximum dive depth is 1,000 meters - after all, it is a drone and does not need to maintain human life onboard. It is designed to be stealthy and deadly, with its warhead having the power of roughly 150 Hiroshima bombs and capable of leveling coastal cities.
This is potentially a serious threat. However, it is important to remember that all we know about the Poseidon comes from the Russian official sources which over the last few months have shown themselves to be capable of an all out deception when it suits them. Much like the "Armata tank" project the Poseidon may exist on paper far more than it does in real life. Hence, even though these reports can not be just dismissed out of hand, it is important to be able to put them in proper perspective.
References
Putin may test underwater nuke 150 times stronger than Hiroshima bomb near Ukrainian border: report
Evan Simko-Bednarski and Patrick Reilly, New York Post, 4 October 2022
Status-6 Oceanic Multipurpose System (wiki)
Russia is trying to sell other countries the new 'cutting-edge' tank that Moscow itself apparently doesn't really want to buy
Michael Peck, Bussiness Insider, 1 September 2022
Russian submarine with nuclear torpedo leaves base | Morning in America (video)
NewsNation, 4 October 2022