The Yuan Wang-class of tracking ships () are used for tracking and support of satellite and intercontinental ballistic missiles by the People's Liberation Army Strategic Support Force of the People's Republic of China (PRC). It is important to note that the class is not a single class of identical design, but instead, a group of different designs grouped under the same series that share the same name. Detailed specifications for every ship have not been released by the PLASSF. Yuan Wang 1 and Yuan Wang 2 are thought to have a displacement tonnage of around 21,000 tons when fully loaded, with a crew of about 470 and a length of about . Their propulsion is from one Sulzer Ltd. diesel engine, with a top speed of 20 knots (37 km/h). The class was first proposed by Premier Zhou Enlai in 1965, and the idea was personally approved by Mao Zedong in 1968. The first two ships of the class, Yuan Wang 1 and Yuan Wang 2, were built at the Jiangnan Shipyard in Shanghai and put to sea on 31 August 1977 and 1 September 1978 respectively. The general designer of this class is . For the first time, this gave the PRC the ability to track launches and satellites that were not over their territory. The first survey mission of the two ships was during May 1980. After being used for tracking of the launches of indigenously developed communications satellites, Yuan Wang 1 and Yuan Wang 2 underwent overhauls in 1986, so they could be used for supporting international satellite launches by the PRC. Two further ships of the class have been built. The first was Yuan Wang 3, which was commissioned on 20 October 1995. The Yuan Wang 4 tracking ship was constructed by China State Shipbuilding Corporation and delivered to the China Satellite Launch and Tracking Control General on 18 July 1999. It had been converted from the previously used Xiang Yang Hong 10 scientific survey ship. Another two Yuan Wang-class vessels were launched in Shanghai in early 2007. Pictures of Yuan Wang 6 were published, and both Yuan Wang 5 and the newly commissioned ship were on duty for the Shenzhou 7 mission. During the Shenzhou spacecraft flights, the four ships were positioned as follows: Yuan Wang 1 in the Yellow Sea Yuan Wang 2 about 1500 km (about 900 statute miles) southwest of French Polynesia