(211231) -- BEIJING, Dec. 31, 2021 (Xinhua) -- Undated file photo shows a carrier-based J-15 fighter jet preparing to land during open-sea combat training. The Chinese navy's Liaoning aircraft-carrier formation returned on Dec. 30, 2021 to a military port in Qingdao, east China's Shandong Province, concluding 20-plus days of open-sea combat training. The exercise, which began on Dec. 9, took the formation into various waters, from the Yellow Sea to the East China Sea and the West Pacific, and has improved the formation's combat capability, according to an official statement. (Photo by Hu Shanmin/Xinhua)