The Sloika Model ("Layer Cake")
The Soviet "layer cake" design was tested on August 12, 1953 with the thermonuclear weapon "Joe-4,"or Reaktivnyi Dvigatel Stalina in Russian (Stalin's Rocket Engine). Created by physicist Andrei Sakharov, it got its name from its "layering" of fusionable material (tritium and deuterium) and fission fuel (uranium). The result was something that more resembled a "boosted" fission bomb than the "true" hydrogen bomb the Soviet's claimed it to be.
Joe-4's blast was equivalent to 400 kilotons of TNT. Russian physicist Yuli Khariton guessed that 15-10% of this yield was due to fusion, while the rest of the force was produced by fission, which occurred at a faster rate than in an average fission bomb because of the fast neutrons being released by the fusion. Unlike a multi-stage hydrogen bomb, the sloika model was a single-stage weapon, and therefore could not be scaled-up indefinitely. The model was abandoned in favor of the truba design, which resembled the United States' "classical super" model.
The first "true" Soviet hydrogen bomb was successfully tested on November 22, 1955.