River-class destroyer escort

In August 1950, the Australian government announced plans to acquire a new class of anti-submarine warfare frigates, based on the British Type 12M (or ) frigate design. Originally six were planned, with construction to be split between Cockatoo Island Dockyard in Sydney and Williamstown Naval Dockyard in Melbourne, but only four were approved. In 1964, the aircraft carrier collided with the destroyer , resulting in the destroyer's sinking. In order to replace the lost capability, the Australian government ordered another two River-class ships, and . They were 370 ft. (113m) long, had a beam of 41 ft. (12.5m), and a draught of 13 ft. (3.9 m). During the 1960s, a quadruple Sea Cat anti-aircraft missile launcher was fitted in place of the Bofors, and one of the Limbo mortars was removed in favour of an Ikara missile launcher. Stuart was the first RAN ship fitted with Ikara, and Derwent the first to carry Sea Cat. In the early 1990s, the missile systems were removed from all active Rivers, with an Army RBS 70 unit available for use if required. ==Operational history==

During their careers, the River-class ships spent most of their time in Australian waters or on multinational exercises, but were regularly deployed to the Far East Strategic Reserve, and saw service during the Indonesia-Malaysia Confrontation. During 1967 and 1968, Stuart and Yarra were used to escort the troop transport on voyages to Vietnam. During the mid-1970s, Yarra underwent a half-life refit, which included the removal of her remaining Limbo, and installation of a Mulloka sonar. Parramatta underwent a more extensive modernisation during the late 1970s, with a new fire control system, modification of the boilers and electrical system, and habitability improvements. Stuart and Derwent underwent similar modernisations between 1979 and 1985. Modernisation was planned for Swan and Torrens during the mid-1980s, but a lack of funding meant that the ships only underwent a half-life refit. At the start of 1984, Stuart became the first RAN vessel permanently assigned to , the new base in Western Australia. In 1992, reports of sexual harassment aboard Swan prompted investigations by the Australian Defence Force and a Senate committee review. ==Decommissioning and fate==

Yarra was decommissioned on 22 November 1985. There were plans to keep her in service as a training vessel, but the decision was to keep active in this role, and Yarra was placed in reserve. Derwent was sunk during explosives testing in 1994. Swan was scuttled as an artificial reef in 1997. Torrens was torpedoed by the Collins-class submarine during a weapons test in 1999. The other three ships were broken up for scrap. ==Specifications==

Note: although these ships are grouped together as a single class, there were many significant differences between the first two units, Yarra and Parramatta (Type 12M), the second two units, Stuart and Derwent (modified Type 12M) and the final two units, Swan and Torrens (Type 12I). • : All four of the Type 12M units were refitted with both the Seacat and Ikara missile systems, replacing 40 mm AA guns and Limbo mortars. During refits in the 1980s the Ikara and Seacat systems were removed and 2x Mark 32 triple torpedo launchers were added to all 5 remaining ships (Yarra was scrapped in 1985). Along with this, the 3 newest ships (Derwent, Swan & Torrens) also got mounts for a removable RBS-70 laser guided missile system. (Parramatta and Stuart were due to be decommissioned in 1991, so were not given the RBS-70's due to their limited remaining service life.) ==Ships==