The Koon shot of Operation Castle was a test of a University of California Radiation Laboratory designed thermonuclear device. The 'dry' two-stage device was known as "Morgenstern". It was tested on 7 April 1954. The predicted yield of Morgenstern, which had a highly innovative secondary stage, was between .33 and 3.5 megatons, with an expected yield of 1 megaton. The actual yield was 110 kilotons. Morgenstern was a 'fissile fizzle'. Post shot analysis showed that the failure was due to the premature heating of the secondary by the neutron flux of the primary. This was a simple design defect, and not related to the unique geometry of the secondary. The UCRL's other shot, the 'wet", i.e. cryogenic, Ramrod device, originally scheduled for the Echo shot was cancelled because it shared the sam