national defense capability"), began to establish a fleet of locally built warships. The Navy acquired shipbuilding capabilities by planning and building high-speed patrol craft such as Baekgu class and Chamsuri class in the 1970s – in November 1972, the ROK Navy launched its first domestically built fast patrol craft to intercept North Korean spy boats. The lead ship (FF 951) of the 2,000-ton Ulsan-class frigates was launched in 1980. The lead ship (PCC 751) of the 1,000-ton Donghae-class corvettes and the lead ship (PCC 756) of the updated Pohang-class corvettes were launched in 1982 and 1984 respectively. The lead ship of, secretly developed, the Dolgorae-class midget submarine was launched in April, 1983. With local shipbuilders, the ROK Navy continued to carry out other shipbuilding programs for such as the Gojunbong-class tank landing ship, mine warfare ship (Wonsan-class minelayer, Ganggyeong-class minesweeper), Cheonji-class logistics support ship, and Cheonghaejin-class submarine rescue ship in the 1980s and 1990s. The Fleet Aviation Unit became the Fleet Air Wing in 1977. The ROK Navy strengthened its naval aviation force by acquiring Grumman S-2 Tracker anti-submarine warfare aircraft and Aérospatiale Alouette III helicopters for shipboard helicopter operations with ex-USN Gearing-class destroyers. In 1986, the Fleet Air Wing became the Air Wing SIX. In 1973 and 1974, the ROK Navy reorganized its fleets into five Naval Sectors. In 1986, the ROK Navy reorganized its fleets: First Fleet, Second Fleet, and Third Fleet. In November 1987, the Headquarters Republic of Korea Marine Corps was re-established; it was disbanded in October 1973 due to budget constraint. On February 22, 1974, a Navy harbor tug (YTL 30) capsized off Tongyeong, resulting in death of 153 Navy, Coast Guard recruits and 6 sailors. 1990s Since the 1990s, the ROK Navy has been trying to build an ocean-going fleet to protect the sea lines of communication as South Korea's dependence on foreign trade increases: In 1989, the Navy mentioned the "Strategic Task Fleet" (Jeollyak-gidong-hamdae) in the Joint Strategic Objectives Plan. The ROK Naval forces began to participated in RIMPAC exercise from 1990 (ROKS Seoul (FF 952), ROKS Masan (FF 953) for RIMPAC 1990). On March 8, 1991, when giving the commencement speech at the ROK Naval Academy's graduation ceremony, President Roh Tae-woo addressed that the Navy should transform into the "blue-water navy". In 1992, the ROK Navy ships - ROKS Chungnam (FF 953) and ROKS Masan (FF 955) of the Cruise Training Unit