Thuc Hoang and the Advanced Simulation and Computing Team

For decades, the U.S. has used computer simulations to maintain the safety and effectiveness of its nuclear stockpile, the result of a self-imposed and then international moratorium on nuclear testing in the 1990s.

However, until recently, most computer systems were too rudimentary to model the complex processes needed to fully assess the reliability of our nuclear weapons.

At the Department of Energy, Thuc Hoang led a multiyear collaboration between the National Nuclear Security Administration and industry leaders to launch El Capitan, the world’s most powerful supercomputer and the first exascale system—a type of supercomputing that uses powerful hardware to perform difficult calculations—dedicated to a national security mission.

“El Capitan provides insights that were previously unattainable, ensuring the United States remains at the forefront of nuclear security,” said David Hoagland, executive principal assistant deputy administrator of the NNSA. “This extraordinary accomplishment represents a transformative leap for both national defense and scientific discovery.”

Launching El Capitan was a gargantuan feat of engineering. To function properly, the machine requires five to nine million gallons of water every day and 30 megawatts of electricity, more than three times the amount of power used by Livermore, California, where the computer resides, according to PCMag.

Hoang, one of the first employees of NNSA’s supercomputing program, began discussing the need to develop exascale technology through public-private partnerships nearly two decades ago. Hoang said collaborative work on the project began in earnest in 2020.

Hoagland credited Hoang with forging partnerships with industry to enable “a revolutionary design of the chipset” needed to make El Capitan work and served as “a project manager, organizer and leader” who had the “technical understanding and vision” to make the computer work.

The new machine can quickly and accurately simulate nuclear explosions with unprecedented levels of detail, predict the aging effects of nuclear weapons and support new fusion experiments. It can perform 1.742 quintillion calculations per second and is 10 times faster than the next fastest supercomputer, according to Hoagland. Before, NNSA could run around one advanced simulation per month. Now, Hoagland said, the agency can run hundreds per year.

“This tool is the backbone for all activities that certify our nuclear stockpile,” said James Peltz, an NNSA physical scientist. “It will allow us to get relevant information and useful data faster than we ever have.”

Launched in January 2025, El Capitan is scaling up its activities, with plans for full deployment later this year. Hoagland said the computer’s capabilities could be applied to support climate modeling, hydrodynamics, astrophysics, non-nuclear weapons and other activities.

Hoang, who came to the U.S. as a Vietnamese refugee in the 1980s, said she wanted to work in federal service from the beginning of her career and is eager to keep pushing the boundaries of discovery at the Energy Department.

“I decided that I wanted to work for the nation—it wasn’t even a question. DOE was my first employer, and it will hopefully be my last,” she said.