Type 631 replenishment tanker

Type 631 tanker is a type of naval auxiliary ship currently in service with the People's Liberation Army Navy (PLAN). Originally designed as a type that is capable of transport both water and oil, but only the oiler version entered service with PLAN.

Type 631 tankers in PLAN service are designated by a combination of two Chinese characters followed by three-digit number. The second Chinese character is You (油), meaning oil in Chinese, because these ships are classified as oilers. The first Chinese character denotes which fleet the ship is service with, with East (Dong, 东) for East Sea Fleet, North (Bei, 北) for North Sea Fleet, and South (Nan, 南) for South Sea Fleet. However, the pennant numbers may have changed due to the change of Chinese naval ships naming convention. Type 631 can be easily distinguished from other transport oilers by its transfer stations amid ship that enables it to carry out underway replenishment missions. Another visual cue of this class is that from the bow to the midsection of the ship, there are three levels of freeboard, while all other Chinese tanker has a smooth curvy transition.