?

Workers prepare China's unmanned submersible "Hailong III" for a deep water test aboard its mothership Dayang Yihao, on April 4, 2018. China's unmanned submersible "Hailong III" dived 4,266 meters below the sea surface in the western Pacific Ocean late Wednesday while conducting a 4,500-meter level deep water test. (Xinhua/Chen Hao)