China has dispatched three naval vessels to Indonesia to help salvage a submarine KRI Nanggala-402 that had sunk off the coast of Bali on April 21. The three Chinese ships arrived in the area in early May and have conducted 13 undersea operations to collect photos and videos of the submarine. The manned submersible "Deep Sea Warrior" aboard the on-duty scientific research vessel Tan Suo 2 has retrieved parts of the wreckage. As humanitarian assistance, the Chinese fleet has entered the crucial stage of the salvaging work.