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One STOBAR carrier: Liaoning was originally built as the 57,000 tonne Soviet Admiral Kuznetsov-class carrier Varyag and was later purchased as a stripped hulk by China in 1998 on the pretext of use as a floating casino, then partially rebuilt and towed to China for completion. Liaoning was commissioned on 25 September 2012, and began service for testing and training. On 24 or 25 November 2012, Liaoning successfully launched and recovered several Shenyang J-15 jet fighter aircraft. She is classified as a training ship, intended to allow the navy to practice with carrier usage. On 26 December 2012, the People's Daily reported that it will take four to five years for Liaoning to reach full capacity, mainly due to training and coordination which will take significant amount of time for Chinese PLA Navy to complete as this is the first aircraft carrier in their possession. As it is a training ship, Liaoning is not assigned to any of China's operation fleets.

Why did the Chinese PLA Navy need 4-5 years for Liaoning to reach full capacity?
this is the first aircraft carrier in their possession