Of all the weapons that the US military can call upon, this is one of the most universally feared. The existence of the Trident II missile is what puts America's enemies off the idea of launching nuclear weapons at the country.
Every Ohio-class submarine has 20 of them, ready to be fired at a moment's notice. Just a single one of them would be enough to wipe North Korea off the map. Five or six of them would completely destroy Russia's electrical grid.