Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954. While most of the Operation Castle tests were intended to evaluate weapons intended for immediate stockpile, or which were already available for use as part of the Emergency Capability Program, Castle Bravo was intended to test a design which would drastically reduce the size and costs of the first generation of air-droppable atomic weapons (the Mk 14, Mk 17 & Mk 24). At long, in diameter, and weighing , the Mk-21 was half the length and one-third the weight of the Mk-17/24 weapons it replaced. Its minimum yield was specified at four megatons.
Mark 22 nuclear bomb
The Mark 22 nuclear bomb (Mk-22) was the first thermonuclear device test by the University of California Radiation Lab (UCRL). The test was part of the "Koon" shot of Operation Castle. The Mk-22 failed to achieve anything like its intended yield due to premature heating of the secondary from exposure to neutrons. As the other UCRL test planned for the Castle series, the liquid fueled "Ramrod" device had the same basic design flaw, that test was canceled. Within a month of the bomb’s failure, the Mk-22 was terminated because the United States Atomic Energy Commission realized there was nothing that could be done to salvage the design.