2M39 Poseidon
2M39 Poseidon is a Russian built nuclear powered and nuclear-armed underwater drone with an indefinite range and can travel 3 times faster than any surface ship. It is capable of an underwater nuclear detonation which would create a massive radioactive tsunami.
The Washington Post claimed the Poseidon underwater drone "defies traditional classification." Michael Petersen, senior research scientist at the Center for Naval Analyses (CNA) in the U.S., described Poseidon as a "Franken-weapon" — a system that combines elements of various types of armaments. According to Petersen, Poseidon "sits somewhere between a torpedo and an unmanned submarine," capable of carrying a nuclear warhead and powered by a nuclear reactor that allows it to cross oceans at virtually unlimited range. He added that Poseidon is intended as a second-strike weapon — designed for retaliatory use in the event of a nuclear war.