concerning the loan of U.S. Navy vessels. From 1955 to 1960, the ROK Navy acquired 42 ex-USN warships including two Cannon-class destroyer escorts. In September 1953, the ROK Navy established the Republic of Korea Fleet, which was responsible for the operation and training of the ships. Fleet Aviation Unit was established in 1957. On July 30, 1960, ROKS Gangwon (DE 72), formerly , sank the North Korean navy patrol ship PBS 371 off the coast of Geojin. 1960s Continuing from the 1950s, the ROK Navy continued to build naval surface forces mainly with World War II-era warships transferred from the U.S. Navy. In May 1963, the ROK Navy acquired its first destroyer ROKS Chungmu (DD 91 and later DD 911), the former , a . On October 3, 1964, ROKS Chungnam (DE 73, later DE 821), formerly , "successfully prosecuted an unidentified submarine contact for more than 17 hours until the contact surfaced and was positively identified as a Soviet with pendant number 017". During the Vietnam War, the ROK Navy dispatched the Naval Transport Group called Baekgu ("Seagull"), which was composed of three Landing Ship Tanks (LST) and two Landing Ship Mediums (LSM). The Republic of Korea Marine Corps sent the 2nd Marine Brigade called Cheongnyong ("Blue Dragon") to South Vietnam. In April 1975, just before the Fall of Saigon, ROKS Gyebong (LST 810), formerly USS Berkshire County (LST-288), and ROKS Bukhan (LST 815), formerly USS Linn County (LST-900), evacuated about 1,300 South Vietnamese and South Koreans from South Vietnam to South Korea. In 1969, the ROK Navy began "Isolated Islands Visiting Program" to support people living in small and remote islands around the peninsula. On January 14, 1967, ROKS Chungnam (DE 73) collided with the wooden-hulled 140-ton coastal ferry Hanil, off Gadeok Island, resulting in death of the ferry's 94 passengers and crew. On January 19, 1967, ROKS Dangpo (PCE 56), the former USS Marfa (PCE-842), was sunk by North Korean coastal artillery north of the demarcation line off the east coast of Korea. was captured by North Korea in January 1968. On June 5, 1970, a navy broadcast vessel (I 2) was captured and abducted by North Korean patrol craft in the vicinity of Yeonpyeong Islands in the West Sea (Yellow Sea). 1970s and 1980s In the 70s, the ROK Navy, through the Park Chung-hee Administration's "Yulgok Plan" (an 8-year national defense plan "to build up self-reliant,