1975, the Navy operated fewer than forty patrol boats along with the coastal junk force. With the collapse of South Vietnam on 30 April 1975, the Navy was expanded with ships from the defunct RVNN. Captured vessels included two patrol frigates, over one hundred patrol craft, and about fifty amphibious warfare ships. Consequently, the navy ballooned in size to become the largest Southeast Asian navy by the mid-1980s, with 1,300 out of its 1,500 vessels captured from the South Vietnamese Navy or US Navy. In the late 1970s the naval infantry (or marines) was formed to be stationed on the areas claimed by the Socialist Republic of Vietnam in the Spratly Islands. The naval infantry is equipped with PT-76 light tanks, BTR-60 personnel carriers and naval infantrymen are armed with AK-74 rifle, AKM-47 assault rifles, Makarov PM pistol (Officers), and PKM machinegun infantry weapons, and more. In March 1988, the Navy fought against the PLAN at Johnson Reef, causing the losses to the Vietnamese of several transport ships and up to 64 deaths. The battle was won by the PLAN who outgunned and outnumbered them, using a fleet of frigates against Vietnamese lightly armed transport ships. This prompted the Navy to modernise its weapons and its overall naval capabilities. Modernization The VPN began modernizing with its contract purchasing two Gepard-class frigates from Russia in 2006. From that point until 2016, a series of changes were implemented to transform the VPN from a purely brown-water navy to one capable of safeguarding its territorial interests in the South China Sea. Its most modern ships in 2011 were its 5 Petya-class frigates (2 Petya-III's from the late 70s, and 3 Petya-III's from the 80s) and a KBO-2000 fast attack craft. The navy attempted a KBO-2000 project with Russia in which the Severnoye Design Bureau designed a KBO-2000 which was constructed in Ba Son Shipyard in Ho Chi Minh City. Only one ship of this class was built by Vietnam, designated HQ-381, but it did not meet the Navy's expectations and so the project was canceled. Organisational structure Organisational levels of Vietnam People's Navy, from highest to lowest are: Naval Headquarters (Bộ tư lệnh Hải quân) takes command of the entire Navy Naval Regions (Vùng Hải quân) 1st, 2nd, 3rd, 4th, 5th Naval Brigade (Lữ đoàn Hải quân) Naval Regiment (Trung đoàn Hải quân) Naval Battalion (Hải đoàn) Squadron (Hải đội) Naval Regions On