The RDS-1 explosion yielded 22 kilotons of TNT, similar to the US Gadget and Fat Man bombs. At Lavrentiy Beria's insistence, the RDS-1 bomb was designed as an implosion type weapon, similar to the Fat Man bomb dropped on Nagasaki, Japan; RDS-1 also had a solid plutonium core. The bomb designers had developed a more sophisticated design (tested later as RDS-2) but rejected it because of the known reliability of the Fat Man type design, the Soviets having received extensive intelligence on the design of the Fat Man bomb during World War II, which was discovered in the espionage case of Julius and Ethel Rosenberg and during the Venona project.