Supercomputers help build nuclear weapons, design aerospace engines, and produce lifesaving drugs. For years, the U.S. had the best and biggest arsenal. Until China got in the game. Lawrence Livermore National Laboratory is one of the great symbols of America’s scientific and military prowess. For six decades, here on this tranquil campus tucked away in the hill country east of San Francisco, where scientists stroll along leafy paths and zip to meetings on bicycles, huge breakthroughs have been made, like the discovery of a half-dozen elements on the periodic table and the detection of a key component of dark matter. Livermore’s biggest claim to fame involves designing the world’s most advanced nuclear warheads—this was the mission of the lab when it was created in 1952 by Edward Teller, father of the hydrogen bomb. To do this, Livermore relies on powerful machines called supercomputers, which hum away inside top-secret, heavily guarded buildings. The U.S. has long