none of his espionage information was of much use, and the Soviet physicists working on the project had to develop their weapon independently. The first Soviet fusion design, developed by Andrei Sakharov and Vitaly Ginzburg in 1949 (before the Soviet Union had a working fission bomb), was dubbed the Sloika, after a Russian layered puff pastry, and was not of the Teller–Ulam configuration, but rather used alternating layers of fissile material and lithium deuteride fusion fuel spiked with tritium (this was later dubbed Sakharov's "First Idea"). Though nuclear fusion was technically achieved, it did not have the scaling property of a "staged" weapon, and their first "hydrogen bomb" test, "Joe 4" is no longer considered to be a "true" hydrogen bomb, and is rather considered a hybrid fission/fusion device more similar to a large boosted fission weapon than a Teller–Ulam weapon (though using an order of magnitude more fusion fuel than a boosted weapon). Detonated in 1953 with a yield equivalent to (only from fusion), the Sloika device did, however, have the advantage of being a weapon which could actually be delivered to a military target, unlike the "Ivy Mike" device, though it was never widely deployed. Teller had proposed a similar design as early as 1946, dubbed the "Alarm Clock" (meant to "wake up" research into the "Super"), though it was calculated to be ultimately not worth the effort and no prototype was ever developed or tested. Attempts to use a Sloika design to achieve megaton-range results proved unfeasible in the Soviet Union as it had in the calculations done in the US, but its value as a practical weapon since it was 20 times more powerful than their first fission bomb, should not be underestimated. The Soviet physicists calculated that at best the design might yield a single megaton of energy if it was pushed to its limits. After the US tested the "Ivy Mike" device in 1952, proving that a multimegaton bomb could be created, the Soviet Union searched for an additional design and continued to work on improving the Sloika (the "First Idea"). The "Second Idea", as Sakharov referred to it in his memoirs, was a previous proposal by Ginzburg in November 1948 to use lithium deuteride in the bomb, which would, by the bombardment by neutrons, produce tritium. In late 1953, physicist Viktor Davidenko achieved the first breakthrough, that of keeping the primary and the