RDS-1 (nuclear weapon)
First fired in a static test on 23 September 1949, RDS-1 was the the first Soviet fission device. "RDS" has several interpretations but appears to be arbitrary; the test was code-named "White Lightning" and called "Joe-1" in the West.
It was a plutonium implosion device with a 22 KT yield. The Soviets put it into limited production, with a goal of 20 to be made per year. RDS-2 (nuclear weapon), a 1951 version of 38 KT yield at half the size and weight, replaced it.