This video goes into detail on Russia’s super-tsunami nuclear weapon, known as Poseidon:
If deployed, this weapon would be devastating to coastal cities. It is an unmanned robotic sub that carries a large nuclear warhead. It is nearly undetectable and can spend months to get to its target if need be. If detonated near a coastal city like New York, both the tsunami and the blast itself would be incredibly destructive. It might also be used to destroy an entire carrier battle group at sea.
“The Doomsday Book” by Marshall Brain lays out this scenario in amazing detail and offers solutions to prevent this doomsday scenario from unfolding. You can pre-order the book today on the pre-order page.