400-ton class ammunition ship is a class of naval auxiliary ship currently in service with the People's Liberation Army Navy (PLAN). The exact type of this class remain unknown as of 2015, because no official information has been released, despite the ships have already been in service around a decade. 400-ton class is the most commonly referred term when describe these ships 400-ton class ammo ship in PLAN service is designated by a combination of an alphabet followed by three-digit number. The alphabet is Y, the abbreviation of Yun, which is for the Chinese character (运), meaning transport. However, the pennant number may have changed due to the change of Chinese naval ships naming convention.