Yankee was originally intended to be a test of a TX-16/EC-16, a weaponized version of the large and complex Ivy Mike device. A small number of emergency capability EC-16s were produced, without being tested, to provide a stop-gap thermonuclear weapon capability in response to the Russian nuclear weapons program. The test device, code-named "Jughead", had been prepared as a backup in case the non-cryogenic Castle Bravo "Shrimp" device failed to work. The test of Jughead was cancelled when the Bravo test was successful, and the cryogenic EC-16s were withdrawn and dismantled.