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 24 nuclear bomb
The Castle Yankee thermonuclear test was the first bomb to use enriched Lithium-6 isotope, up to perhaps 40% enrichment (the earlier Castle Bravo test had used the same enriched lithium combination but was not weaponised i.e. was not built as a deployable bomb). The device tested was called the Runt II design; it was reportedly very similar to the Runt design tested in Castle Romeo, other than the enrichment level.