Type 002 and Type 003), and helicopter carriers (Type 075) and large amphibious warfare vessels (Type 071) capable of mobilizing troops at long distances. On the medium and low end, there would be more economical multi-role capable frigates and destroyers (Luhu, Jiangwei II and Jiangkai classes), corvettes (Jiangdao class), fast littoral missile attack craft (Houjian, Houxin and Houbei classes), various landing ships and light craft, and conventionally powered coastal patrol submarines (Song class). The obsolete combat ships (based on 1960s designs) will be phased out in the coming decades as more modern designs enter full production. It may take a decade for the bulk of these older ships to be retired. Until then, they will serve principally on the low end, as multi-role patrol/escort platforms. Their use could be further enhanced in the future by being used as fast transports or fire support platforms. This system of phasing out would see a reversal in the decline in quantity of PLAN vessels by 2015, and cuts in inventory after the end of the Cold War could be made up for by 2020. Between 2001 and 2006 there was a rapid building and acquisition program, a trend which continued. There were more than a dozen new classes of ships built in those five years, totaling some 60 brand new ships (including landing ships and auxiliaries). Simultaneously, dozens of other ships have been either phased out of service or refitted with new equipment. Submarines play a significant role in the development of the PLAN's future fleet. This is made evident by the construction of a new type of nuclear ballistic missile submarine, the Type 094 and the Type 093 nuclear attack submarine. This will provide the PLAN with a more modern response for the need of a seaborne nuclear deterrent. The new submarines will also be capable of performing conventional strike and other special warfare requirements. The European Union has provided much of the propulsion technology for the PLAN's modernization. Ronald O'Rourke of the Congressional Research Service reported that the long-term goals of PLAN planning include: Assert or defend China's claims in maritime territorial disputes and China's interpretation of international laws relating to freedom of navigation in exclusive economic zones (an interpretation at odds with the U.S. interpretation); Protect China's sea lines of communications to the Persian Gulf, on which China relies for some of its energy imports. During the military parade on