“I’m in Barbados doing research, and I’m standing under a 100 caliber barrel. The thing looks big enough to crawl into, but not quite. And the barrel just keeps going and going. Big enough that I have to trudge through the wet grass a ways to get some perspective on the whole thing. This cannon is so damn big it has a structure around the barrel to keep it rigid. It’s mounted on a concrete pad the size of an office building’s foundation. And there’s this huge space for recoil: a dark pit that...