Navy Headquarters, which controlled the three fleet commands, was subordinate to the PLA General Staff Department. In 1987, China's 1,500 km coastline was protected by approximately 70 diesel-powered Romeo- and Whiskey-class submarines, which could remain at sea only a limited time. Inside this protective ring and within range of shore-based aircraft were destroyers and frigates mounting Styx anti-ship missiles, depth-charge projectors, and guns up to 130 mm. Any invader penetrating the destroyer and frigate protection would have been swarmed by almost 900 fast-attack craft. Stormy weather limited the range of these small boats, however, and curtailed air support. Behind the inner ring were Coastal Defense Force personnel operating naval shore batteries of Styx missiles and guns, backed by ground force units deployed in depth. 1990s and 2000s As the 21st century approached, the PLAN began to transition to an off-shore defensive strategy that entailed more out-of-area operations away from its traditional territorial waters. Between 1989 and 1993, the training ship Zhenghe paid ports visits to Hawaii, Thailand, Bangladesh, Pakistan, and India. PLAN vessels visited Vladivostok in 1993, 1994, 1995, and 1996. PLAN task groups also paid visits to Indonesia in 1995; North Korea in 1997; New Zealand, Australia, and the Philippines in 1998; Malaysia, Tanzania, South Africa, the United States, and Canada in 2000; and India, Pakistan, France, Italy, Germany, Britain, Hong Kong, Australia, and New Zealand in 2001. In March 1997, the Luhu-class guided missile destroyer Harbin, the Luda-class guided missile destroyer Zhuhai, and the replenishment oiler Nancang began the PLA Navy's first circumnavigation of the Pacific Ocean, a 98-day voyage with port visits to Mexico, Peru, Chile, and the United States, including Pearl Harbor and San Diego. The flotilla was under the command of Vice Admiral Wang Yongguo, the commander-in-chief of the South Sea Fleet. The Luhu-class guided missile destroyer Qingdao and the replenishment oiler Taicang completed the PLA Navy's first circumnavigation of the world (pictured), a 123-day voyage covering between 15 May – 23 September 2002. Port visits included Changi, Singapore; Alexandria, Egypt; Aksis, Turkey; Sevastopol, Ukraine; Piraeus, Greece; Lisbon, Portugal; Fortaleza, Brazil; Guayaquil, Ecuador; Callao, Peru; and Papeete in French Polynesia. The PLA naval vessels participated in naval exercises with the French frigates Nivôse and Prairial, as well as exercises with the Peruvian Navy. The flotilla was under the command of Vice Admiral Ding Yiping, the commander-in-chief of the North Sea Fleet, and Captain Li Yujie