RDS-4 was a soviet nuclear bomb. It was the Soviet Union's first mass produced tactical nuclear weapon. It used a plutonium implosion assembly and had a nominal yield of 30 kilotons. The bomb was delivered from a Tu-4 and Tu-16 aircraft.
It was first tested at Semipalatinsk Test Site

Semipalatinsk Test Site

The Semipalatinsk Test Site was the primary testing venue for the Soviet Union's nuclear weapons. It is located on the steppe in northeast Kazakhstan , south of the valley of the Irtysh River...

, on August 23, 1953. The bomb was dropped from a IL-28

Ilyushin Il-28

The Ilyushin Il-28 is a jet bomber aircraft of the immediate postwar period that was originally manufactured for the Soviet Air Force. It was the USSR's first such aircraft to enter large-scale production. It was also licence-built in China as the Harbin H-5. Total production in the USSR was 6,316...

aircraft on an altitude of 11 km and exploded on 600 m, with a yield of 28 kt.