Bulletin of the Atomic Scientists

Since last fall, Air Force Gen. Kevin Chilton, commander of U.S. Strategic Command, has been stumping for the so-called Reliable Replacement Warhead (RRW) Program, which would develop new nuclear warheads to swap into the U.S. arsenal. In a sit-down with Wall Street Journal editors last November, Chilton held aloft a prop to make his case: "I remember what these things were for. I bet you don't. It's a vacuum tube. My father used to take these out of the television set in the 1950s and 1960s down to the local supermarket to test them and replace them."

Nuclear deterrence is a rather subjective concept: How many weapons are enough to ensure deterrence? How difficult is it to achieve and maintain deterrence? How important are the technical details of a country’s nuclear forces, such as the size, configuration, and readiness, to the goal of maintaining deterrence? The answers to these questions vary across recent history and across geographic areas.