RDS-3 was the third atomic bomb developed by the Soviet Union in 1951, after the famous RDS-1 and RDS-2. It was called Marya in the military. The bomb had a composite design with a plutonium core inside a uranium shell, providing an explosive power of 40 kilotons.
Testing
RDS-3 was tested on October 18, 1951, being air-dropped. It was the first such test of a nuclear device by the Soviets, known as Joe-3 in the West.
References
RDS-3 Wikipedia(Text) CC BY-SA