RDS-6s

RDS-6s (Russian: РДС-6с, from the encrypted Soviet codename for their atomic bombs Russian: Реактивный Двигатель Специальный, lit. 'special jet engine'; American codename: Joe 4) was the first Soviet test of a thermonuclear weapon that occurred on August 12, 1953, that detonated with a force equivalent to 400 kilotons of TNT.

RDS-6 utilized a scheme in which fission and fusion fuel (lithium-6 deuteride) were "layered", a design known as the Sloika (Russian: Слойка, named after a type of layered puff pastry) model in the Soviet Union. A ten-fold increase in explosive power was achieved by a combination of fusion and fission. A similar design was earlier theorized by Edward Teller, but never tested in the U.S., as the "Alarm Clock".