In the early 1950s a need arose in the Soviet Union for a heavy transport and assault helicopter capable of airlifting cargo weighing up to 6 tons (13,230 lbs) - primarily artillery systems. The chief Soviet "helicopter maker" - OKB-329 headed by Mikhail L. Mil - took on this important task. The prototype of the V-6 (eventually redesignated Mi-6), which first flew in June 1957, was a much larger machine. For the first time not only in the Mil OKB's practice but also in the world helicopter design practice, the powerplant consisted of two gas turbine engines; another peculiarity was the use of auxiliary wing offloading the main rotor in cruise flight. The Mi-6 provided a major boost to the Soviet Air Force's capability. In 1959 it served as the basis for the unconventional Mi-10 capable of straddling bulky loads. In 1967, however, Mil truly amazed the world by bringing out the mighty V-12 capable of lifting a 25-ton (55,110-lb) payload. This machine was destined to remain in prototype form; yet in 1977 the OKB achieved a major success with the smaller but more advanced Mi-26, which remains the world's largest production helicopter and, like the Mi-6, has rendered invaluable service in both civil and military applications. This book covers the development history and design of all the various types in detail and is well illustrated with numerous photos and line drawings.