<P> RDS - 5 was a small plutonium based device, probably using a hollow core . Two different versions were made and tested . </P> <P> RDS - 6, the first Soviet test of a hydrogen bomb, took place on August 12, 1953, and was nicknamed Joe 4 by the Americans . It used a layer - cake design of fission and fusion fuels (uranium 235 and lithium - 6 deuteride) and produced a yield of 400 kilotons . This yield was about ten times more powerful than any previous Soviet test . When developing higher level bombs, the Soviets proceeded with the RDS - 6 as their main effort instead of the analog RDS - 7 advanced fission bomb . This led to the third idea bomb which is the RDS - 37 . </P> <P> A much lower - power version of the RDS - 4 with a 3 - 10 kiloton yield, the RDS - 9 was developed for the T - 5 nuclear torpedo . A 3.5 kiloton underwater test was performed with the torpedo on September 21, 1955 . </P> <P> The first Soviet test of a "true" hydrogen bomb in the megaton range was conducted on November 22, 1955 . It was dubbed RDS - 37 by the Soviets . It was of the multi-staged, radiation implosion thermonuclear design called Sakharov's "Third Idea" in the USSR and the Teller - Ulam design in the USA . </P>

When did the soviet union develop nuclear weapons