Castle Koon

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Castle Koon
Country United States
Test series Operation Castle
Test site Bikini Atoll
Date April 7, 1954
Test type Atmospheric
Yield 110 kt
Test chronology

The Koon shot of Operation Castle was a test of a University of California Radiation Laboratory (UCRL), now Lawrence Livermore National Laboratory (LLNL) 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 0.33 and 3.5 megatons, with an expected yield of 1 megaton. The actual yield was 110 kilotons. Morgenstern was thus 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 same simple design defect as Morgenstern. The name "Morgenstern" (German for Morning Star) was chosen because of the shape of the secondary. The secondary consisted of a central sphere from which spikes were radiating, resembling a morning star / mace. The spikes may have been an idea from Teller and colleagues to use implosive jets to compress the thermonuclear core. It would be well over two decades before weapons were designed which utilized a secondary concept similar to that which went untested in the Koon shot.


  • Hansen, Chuck, "The Swords of Armageddon: U.S. Nuclear Weapons Development since 1945" (CD-ROM). PDF, 2,600 pages, Sunnyvale, CA, Chukelea Publications, 1995, 2007. ISBN 978-0-9791915-0-3 (2nd Ed.)