12 August 1953 - Soviet 'RDS-6' test RDS-6, nicknamed “Joe 4” by
the United States, was the fifth nuclear test conducted by the
Soviet Union. With a force equivalent to 400 kilotons of TNT
(around 30 times the Hiroshima bomb’s yield), it was the
country’s largest test until then. RDS-6 was part of the Soviet
Union’s efforts to catch up with the United States, which had
detonated its first thermonuclear device with the ‘George’ test
two years earlier in May 1951. The weapon used a design known as
the Sloika model (Слойка, named after a type of layered puff
pastry) in which fission and fusion fuel were "layered". Soviet
lead physicist Yulii Khariton estimated that 15 to 20% of its
yield was based on fusion and the rest on fission. Because the
potential yield of the Sloika design was limited to around one
megaton (roughly 75 times the yield of the Hiroshima bomb), it
was later abandoned. The multi-stage Teller-Ulam hydrogen bomb
design on the side of the United States, in contrast, could be
scaled up indefinitel