The Mark 16 nuclear bomb was a large American thermonuclear bomb (hydrogen bomb), based on the design of the Ivy Mike, the first thermonuclear device ever test fired. The Mark 16 is more properly designated TX-16/EC-16 as it only existed in Experimental/Emergency Capability (EC) versions.
The TX-16 was the only deployed thermonuclear bomb which used a cryogenic liquid deuterium fusion fuel, the same fuel used in the Ivy Mike test device. The TX-16 was a weaponized version of the Ivy Mike design. This required both a considerable reduction in weight of the explosive package and the replacement of the elaborate cryogenic system with vacuum flasks for replenishing boiled-off deuterium. The carrier aircraft was to be the B-36 as modified under Operation Barroom. Only one B-36 was so modified. The TX-16 shared common forward and aft casing sections with the TX-14 and TX-17/24 and in the emergency capability (EC-16) version was almost indistinguishable from the EC-14. A small number of EC-16s were produced to provide a stop-gap thermonuclear weapon capability in response to the Russian nuclear weapons program. The TX-16 was scheduled to be tested as the Castle Yankee "Jughead" device until the overwhelming success of the Castle Bravo "Shrimp" test device rendered it obsolete.