China's self-developed 4,500-meter-level unmanned submersible Qianglong 3 will conduct its first dive in the South China Sea on Friday. It’s projected to reach a depth of 3,500 meters. The orange clownfish-shaped autonomous underwater vehicle is 3.5 meters long, 1.5 meters high and weighs 1.5 tons. [Photo/Xinhua]

Members of the Qianlong 3 research group check the unmanned submersible before the dive on April 19, 2018. [Photo/Xinhua]

An April 15 photo shows Dayang Yihao, which carried the unmanned submersible Qianglong 3 and a research group of 70 people from Xiamen to the South China Sea. [Photo/Xinhua]

A photo taken on Dayang Yihao in Xiamen, East China’s Fujian province, on April 15, 2018. [Photo/Xinhua]