Regarding the design of a nuclear fission trigger that ignites a fusion bomb.
Levitation gave the imploding shell time to acquire momentum before it hit the core. Nuclear-weapons designer Theodore B. Taylor explained the principle to the writer John McPhee once without naming it: “The way to get more energy into the middle was to hit the core harder. When you hammer a nail, what do you do? Do you put the hammer on the nail and push?” The solid Fat Man core had been pushed; levitation hammered. And because it increased efficiency, levitation also made it possible to design bombs of smaller diameters than Fat Man, lighter weapons more easily transportable by plane. The composite core, as [Hans] Bethe points out, used less plutonium and resulted in increased yield as well, both important advantages.
Part 1, Chapter 10