Many people know about russian hydrogen bomb with about 100megaton projected (50 megaton tested) power.
usualy mosts sources say that it was just test device that cant be used because there was no way to deliver it, however that is not true.

But recently on russian tv I saw that it actualy was possible to use. they designed special transcontinental torpedo, which could deliver that bomb near usa shore, and explosison would be so powerfull that it could create cunami which would be able to flood all NewYork.
also there was project to make bomb ship, with so big power that explosion would result end of the world.

fortunately these projects were not finished.