Simon nodded. "The Russians set it off about ten months before Mr. Dyson wrote this." He put his hand on the document. "The interesting takeaway was that despite its fifty-megaton yield, it didn’t do as much damage as expected. Why? Because the earth is hard and the atmosphere is quite yielding—and only gets more so the higher up you go. So the explosion sort of ricocheted off the ground and went the only way it could go and basically punched a hole through the atmosphere and dissipated its power into the void. For those in the know, the lesson learned was that making bigger bombs was a waste of resources. But Freeman Dyson understood that large bombs could still have military effect provided you worked out a way to detonate them in a medium that would contain the blast and absorb its energy, rather than just venting it into outer space. Such a medium is water. The scenario he describes here, starting on about page 6, is that a very large hydrogen bomb—much bigger than the Tsar Bomba, even—is deposited on the floor of the ocean offshore from the coastal region to be attacked. This is easy to do covertly using a submarine or just kicking it off a ship. When the bomb is later detonated, all its energy is deposited into the surrounding water, creating an artificial tsunami that crests over the nearby coastline and, to borrow a homely phrase from the Yanks, breaks a lot of things and hurts a lot of people. And I do mean a lot , in Dyson’s scenario. No one ever accused that man of not thinking big."