The Antonov An-225 Mriya is a strategic airlift cargo aircraft that was designed by the Soviet Union's Antonov Design Bureau in the 1980s. It is powered by six turbofan engines and is the longest and heaviest airplane ever built, with a maximum takeoff weight of 640 tonnes (710 short tons). The Antonov An-225, initially developed for the task of transporting the Buran spaceplane, was an enlargement of the successful Antonov An-124. The first and only An-225 was completed in 1988
Ukraine’s Antonov Airlines operates seven An-124s, as well as the massive An-225, the largest cargo plane in the world. Antonov was looking to convert the An-124 into using western avionics and engines.
Antonov has helped China's Shaanxi Aircraft Company to produce a much improved version of the Y-8 called the Y-9, which can carry 20 tons of cargo. In addition, China held discussions with Antonov regarding the possible co-production of the 150-ton capacity An-124 Ruslan, which exceeds the 120-ton capacity of the US C-5 transport.
China plans to build more than 1,000 heavy strategic transport aircraft. In January, the China Daily reported that the People's Liberation Army Air Force was preparing to develop a new fleet of stealth fighters and heavy transport aircraft. The latter, the Xian Y-20 transport, was in particularly high demand, given Beijing's lack of a "fast and reliable platform" to deliver arms and soldiers over long distances.
Heavy transport aircraft are critical to extend the operational range of China's airforce. They can be used for mid-air refueling. It will also allow for rapid deployment of troops and tanks to different locations.
SOURCEs- Global security, wikipedia, Foxtrot alpha, Milnavigator