Diablo was one of Livermore's steps toward a deployable hydrogen bomb. The shot tested a two-stage thermonuclear design at reduced scale: a boosted "Swan" primary — the compact, efficient fission trigger the laboratory was perfecting across Operation Plumbbob — was fired inside a mock-up of the larger weapon it was meant to ignite. The secondary stage added to the total, which reached 17 kilotonnes, a little above the predicted range; the full-scale version of the design was slated for testing in the Pacific the following year. Like the other University of California Radiation Laboratory shots of the series, Diablo was named for a North American mountain — Mount Diablo, the peak that stands over the East Bay of California, near Livermore itself.