Photo taken on July 23, 2017 shows the submersible "Explorer" on China's independently-made marine science expedition vessel "Kexue." (Photo/Xinhua)

"Explorer," China's independently-developed unmanned submersible, carried out its first experimental mission in the northern reaches of the South China Sea on July 24. It is expected to explore underwater for 20 hours, Xinhua News Agency reported.

The submersible is 3.5 meters long, 1.5 meters wide, and 1.5 meters high, and has four red fin-shaped propellers. It can work at a maximum depth of 4,500 meters under water.

Zhao Hongyu, an associate researcher at the Shenyang Institute of Automation of Chinese Academy of Sciences, explained that the "Explorer" is not tethered to its mother ship. It works autonomously in accordance with default procedures.

Scientists will identify spots with research value after the "Explorer" finishes its mission in this cold area of the South China Sea, and then carry out fine investigations with a remote-operated submarine.

Unlike unmanned submersibles, remote-operated submarines are tethered to the mother ship and can carry more equipment to conduct finer investigation and operations.

"Explorer" is loaded on "Kexue," China's independently-made marine science expedition vessel, which is now carrying out a maritime scientific expedition in South China Sea.