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.
Operation Crosstie
The Faultless test was a calibration test conducted in a mine cavity 3,200 feet beneath the Hot Creek Valley near Tonopah, Nevada, with a yield of around 1 megaton. This test was conducted to see if the land was fit for testing a 5 megaton thermonuclear warhead for the Spartan missile. The test failed because of the large degree of faulting that resulted in the area around the test. It was decided that the land was unfit for multi-megaton nuclear tests, so a similar calibration test was conducted at Amchitka Island, Alaska, in the fall of 1969 during Operation Mandrel.