In a nondescript building on Kirtland Air Force Base on the high desert of New Mexico, liquid-cooled supercomputers gurgle and hum their way through some of the most complex math problems the U.S. government seeks to solve: simulating how hypersonic nuclear weapons would move through the earth's atmosphere, or what would happen if one nuclear warhead detonated near another. For more than a decade, the chips handling this secretive and demanding work came from mainstream semiconductor firms like Nvidia or Advanced Micro Devices. But with those companies increasingly designing their chips for artificial intelligence and facing supply shortages, the managers in charge of the systems at Sandia National Laboratories, which operates the machines at Kirtland and is one of three U.S. labs tasked with developing and maintaining the nation's nuclear weapons arsenal, are increasingly unsure how they will find computing power for high-precision scientific work like theirs.