The Koon shot of Operation Castle was a test of a thermonuclear device designed at the University of California Radiation Laboratory (UCRL), now Lawrence Livermore National Laboratory (LLNL). The "dry" two-stage device was known as "Morgenstern", and had a highly innovative secondary stage. It was tested on April 7, 1954. The predicted yield was between 0.33 and 3.5 megatons, with an expected yield of 1 megaton. The actual yield was 110 kilotons. Morgenstern was thus a fizzle.