Weapons experts and Western officials have expressed particular concern about one Russian ‘super-weapon,’ the Poseidon 2M39 torpedo. Development of the torpedo is moving fast with Russian President Vladimir Putin requesting an update on a “key stage” of the tests in February from his defense minister Sergei Shoigu, with further tests planned this year, according to multiple reports in state media.

This unmanned stealth torpedo is powered by a nuclear reactor and intended by Russian designers to sneak past coastal defenses — like those of the US — on the sea floor.

The device is intended to deliver a warhead of multiple megatons, according to Russian officials, causing radioactive waves that would render swathes of the target coastline uninhabitable for decades.

In November, Christopher A Ford, then assistant secretary of state for International Security and Non-Proliferation, said the Poseidon is designed to “inundate U.S. coastal cities with radioactive tsunamis.”