Reis teamed up with senior scientists and military personnel to draft a program that could validate the performance of the weapons and simulate the effects of aging on the weapons and their safety—what he called Science Based Stockpile Stewardship. The three national labs with weapons programs—Los Alamos National Lab, Lawrence Livermore National Lab, and Sandia National Laboratories—were already working on large experiments for testing components of nuclear weapons. However, there wasn’t nearly enough computing capacity to run all of the required simulations. Fortunately, Reis had previously been the director of DARPA and convinced a manager there to lead what would become the Accelerated Strategic Computing Initiative, a program that would significantly increase the computing power available to the weapons labs. Today, the Stockpile Stewardship program operates on a three-pillared approach, combining theory, simulation, and experiment, and runs mainly out of those three labs as well as the Nevada National Security Site.

The goal of the program is to issue an annual report to Congress offering complete confidence that the nuclear arsenal is 100 percent reliable, even as the radioactive pits inside of the weapons age and undergo molecular changes. But the pit is just one part of a weapon; there are several thousand other components that go into the device. Conventional explosives must set off chain reactions. The pit must be secured so it doesn’t jostle around and detonate accidentally, and the weapon must sit inside a casing that protects it from the outside world. Nuclear warheads require a delivery method, such as a gravity bomb from inside a plane, an intercontinental ballistic missile, or a submarine-launched ballistic missile. The nuke must continue to work even if another country attempts to stop it (say, with another nuke).