The rank of admiral of the fleet (or "fleet admiral") (Russian: admiral flota, aдмирал флота) was the highest naval rank of the Soviet Union from 1940 to 1955 and second-highest from 1962.
The rank has a rather confusing history. It was first created by a Decree of the Presidium of the Supreme Soviet in 1940 as an equivalent to general of the army, but was not used until 1944, when Ivan Isakov and Nikolai Kuznetsov were promoted to the rank.
The 1944 insignia featured four Nakhimov stars, but when the rank was declared equivalent to the marshal of the Soviet Union in 1945, they were replaced with a single, bigger star to look similar to marshal's shoulder boards. The two existing admirals of the fleet were given this new 'big' marshal's star. So from 1945 to 1962, there was no intermediate rank equivalent to general of the army in between admiral and admiral of the fleet.
The rank was abolished in March 1955 with the creation of the rank of admiral of the fleet of the Soviet Union but restored in 1962 as the second-highest navy rank. Holders of the ranks were given a smaller marshal's star since then. As of February 2013 the smaller marshal's star has been instituted on fleet admiral shoulder boards - equivalent of general of the army. As of February 2013 there are no active duty Russian Navy officers holding that rank.
According to Kuznetsov, the rank was conferred on him by Joseph Stalin in May 1944.
In 1948 Kuznetsov was demoted two grades to the rank of rear admiral. Soon before Stalin's death, however, Kuznetsov was again restored as a fleet admiral and was among the two admirals to receive the rank of fleet admiral of the Soviet Union upon its official creation in 1955, the other being Ivan Isakov.