The U.S. name , Alarm Clock , came from Teller : he called it that because it might " wake up the world " to the possibility of the potential of the Super . The Russian name for the same design was more descriptive : Sloika ( ) , a layered pastry cake . A single-stage Soviet Sloika was tested on August 12 , 1953 . No single-stage U.S. version was tested , but the Union shot of Operation Castle , April 26 , 1954 , was a two-stage thermonuclear device code-named Alarm Clock . Its yield , at Bikini , was 6.9 megatons
Union
Castle Union
Nuclear weapon design