IBM's Sequoia has taken the top spot on the list of the world's fastest supercomputers for the US.
The newly installed system trumped Japan's K Computer made by Fujitsu which fell to second place.
It is the first time the US can claim pole position since it was beaten by China two years ago.
Sequoia will be used to carry out simulations to help extend the life of aging nuclear weapons, avoiding the need for real-world underground tests.
It is installed at the US Department of Energy's Lawrence Livermore National Laboratory in California.
"While Sequoia may be the fastest, the underlying computing capabilities it provides give us increased confidence in the nation's nuclear deterrent," said National Nuclear Security Administration (NNSA) administrator Thomas D'Agostino.
