China's unmanned submersible Qianlong III is retrieved from its second dive into the sea back to the Chinese research vessel Dayang Yihao (Ocean No. 1), on April 22, 2018. The submersible, diving for its second sea test, entered the 3,850-meter-deep sea area and traveled 156.82 km during the nearly 43-hour voyage from April 21 to 22. (Xinhua/Liu Shiping)