To secure independence from the West, industry leaders mandated that the USSR develop its own sound technologies, rather than taking licenses on Western sound systems. Two Soviet scientists, Alexander Shorin in Leningrad (present-day St. Petersburg) and Pavel Tager in Moscow, conducted research through the late 1920s on complementary sound systems, which were ready for use by 1930. The implementation process, including the cost of refitting movie theaters, proved daunting, and the USSR did not complete the transition to sound until 1935. Nevertheless, several directors made innovative use of sound once the technology became available. In "Enthusiasm: The Symphony of Donbass" (1930), his documentary on coal mining and heavy industry, Dziga Vertov based his soundtrack on an elegantly orchestrated array of industrial noises. In "The Deserter" (1933) Pudovkin experimented with a form of "sound counterpoint" by exploiting tensions and ironic dissonances between sound elements and the image track. And in "Alexander Nevsky", Eisenstein collaborated with the composer Sergei Prokofiev on an "operatic" film style that elegantly coordinated the musical score and the image track.