They have nukes speculated to be double or so the yield of the Tsar Bomba. Those nukes are aboard unmanned submarine drones, nuclear-powered, which coast around the ocean for a period of months.
People were butthurt when they built them because they are overpowered.
The idea is that they explode on the shoreline of an enemy nation, and the water vapor which is generated and falls on the land will be contaminated with radioactive material from the explosion, making a large area unsafe for humans.