The AK-47 is a selective-fire, gas-operated 7.62×39 mm rifle developed in the Soviet Union by Mikhail Kalashnikov. Design and development began in 1945 and in 1948, the rifle entered service with select units of the Soviet Army. In early 1949, it was fully adopted by all Soviet Armed Forces as well as most members of the Warsaw Pact. Even after almost 70 years, the AK and its many variants are still the most prolific rifles in the world. Their fame is due in part to their unwavering reliability in virtually any conditions, low manufacturing cost and ease of operation. It is estimated that one fifth of all firearms in use in the world today belong to the Kalashnikov family.