Editing Nuclear weapon design (section)

==={{Anchor|Alarm Clock}}Alarm Clock/Sloika===
[[File:Castle Union.gif|thumb|Castle-''Union'', 6.9&nbsp;megatons.]]
The first effort to exploit the symbiotic relationship between fission and fusion was a 1940s design that mixed fission and fusion fuel in alternating thin layers. As a single-stage device, it would have been a cumbersome application of boosted fission. It first became practical when incorporated into the secondary of a two-stage thermonuclear weapon.<ref>"The 'Alarm Clock' ... became practical only by the inclusion of Li6 (in 1950) and its combination with the radiation implosion." Hans A. Bethe, [https://fas.org/nuke/guide/usa/nuclear/bethe-52.htm Memorandum on the History of Thermonuclear Program] {{webarchive |url=https://web.archive.org/web/20160304030002/https://fas.org/nuke/guide/usa/nuclear/bethe-52.htm |date=March 4, 2016}}, May 28, 1952.</ref>

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.{{sfn|Rhodes|1995|p=256}} The Russian name for the same design was more descriptive: Sloika ({{langx|ru|Слойка}}), a layered pastry cake. A single-stage Soviet Sloika was tested as [[RDS-6s]] on August 12, 1953. No single-stage U.S. version was tested, but the code named [[Castle Union]] shot of [[Operation Castle]], April 26, 1954, was a two-stage thermonuclear device code-named Alarm Clock. Its yield, at [[Bikini Atoll|Bikini]], was 6.9 megatons.{{Citation needed|date=June 2021}}

Because the Soviet Sloika test used dry lithium-6 deuteride eight months before the first U.S. test to use it (Castle Bravo, March 1, 1954), it was sometimes claimed that the USSR won the H-bomb race, even though the United States tested and developed the first hydrogen bomb: the Ivy Mike H-bomb test. The 1952 U.S. Ivy Mike test used cryogenically cooled liquid deuterium as the fusion fuel in the secondary, and employed the D-D fusion reaction. However, the first Soviet test to use a radiation-imploded secondary, the essential feature of a true H-bomb, was on November 23, 1955, three years after Ivy Mike. In fact, real work on the implosion scheme in the Soviet Union only commenced in the very early part of 1953, several months after the successful testing of Sloika.{{Citation needed|date=June 2021}}