Rothesay-class frigate

The Rothesay class, or Type 12M frigates were a class of frigates serving with the Royal Navy, South African Navy (where they were called President-class frigates) and the New Zealand Navy.

The original Type 12 frigates, the Whitby-class frigate, were designed as first-rate ocean-going convoy escorts in light of experience gained during World War II. However, such were the capabilities and potential of the design that it was deemed suitable for use as a fast fleet anti-submarine warfare escort. As such, a repeat and improved Type 12 design was prepared, known as the Type 12M (M for "modified"), and known as the Rothesay class after the lead ship. A total of twelve vessels were constructed, with the lead ship being laid down in 1956, two years after the last Whitby. The design was successful and popular, serving the Royal Navy and South African Navy well into the 1980s and serving with distinction in the Falklands war.

Design
The Type 12M retained the excellent hull design of the Type 12, that allowed high cruising speed to be maintained in heavy seas, critical to the success of anti-submarine warfare in the era of the threat of the high-speed Soviet submarine. Armament and the propulsion plant remained largely unchanged. The main external differences were an enlarged raked and streamlined funnel (retroactively fitted to the Whitbys) and a modified after deckhouse, enlarged to carry the Sea Cat anti-aircraft missile launcher and its associated GWS-20 director and handling rooms as it became available. This weapon was not available originally, therefore a single 40 mm Bofors Mark 7 gun was shipped in lieu. The arrangement of the torpedo tubes was also altered in the new design, with 4 fixed tubes firing aft at 45° on each beam, in front of a trainable twin mounting; the reverse of the arrangement on the Whitbys. A suitable weapon was never developed for these tubes, so they remained unused, or were never fitted. Internally, electrical generation capacity was increased to handle the increasing demands created by improved ships electronics. Accommodation standards were also improved, with partial bunking and air conditioning. Such was the success of the Rothesay design that it was elaborated into the excellent general purpose Leander-class frigate, the Type 12I.

Modification
Increasing submarine performance in the 1960s demanded detection and engagement of targets at a greater distance from the fleet. Detection was improved with new sonar designs such as the Type 177 search and Type 199 Variable depth. To attack targets at a greater range, the Royal Navy adopted the MATCH (Medium-range Anti-submarine Torpedo Carrying Helicopter) system. MATCH was essentially the Westland Wasp HAS.1, a lightweight navalised helicopter small enough to operate from a small hangar and flight deck that could be fitted to contemporary frigate designs yet large enough to carry a pair of anti-submarine homing torpedoes (US Mark 44 or 46 types), allowing engagement of underwater targets at some distance from the parent vessel, outside the range of the shipboard Limbo anti-submarine mortars. To allow MATCH to be carried, all of the Type 12M class were modified and modernised, beginning with Rothesay from 1966 and finishing in 1972.

The after superstructure was removed, along with the foremost Limbo mortar, with the well being plated over to create a small flight deck. A small hangar was constructed in front of this, on top of which the GWS-20 Sea Cat missile and director was (finally) shipped. The mainmast was replaced by am enclosed design, carrying the Type 1010 IFF antennas, with the funnel height was increased to carry the hot exhaust gasses over the taller superstructure. The electronics fit was also upgraded from the World War II era sets fitted in the Whitbys. A large, enclosed foremast replaced the short lattice, carrying the distinctive "half cheese" antennas associated with the Type 993 target indicator. The Mark 6M director was replaced with the MRS3 system carrying radar Type 903, allowing the removal of the Type 277Q height finder. Additionally, Knebworth/Corvus 3-inch countermeasures launchers were fitted on either side of the bridge, as were a pair of World War II vintage 20 mm Oerlikon guns for "policing" work (and strictly limited anti-aircraft defence).

The extensive modifications of the Rothesays brought their fighting capabilities into line with the that of the original Leander-class vessels. Later in the early 1980s, Rothesay, Yarmouth and Plymouth had an extensive refit, which included upgrading their main radar and target indicator to the 994 radar which was essentially a version of the Plessy AWS1 in the old antenna, giving in particular faster updating, to about one second delay on the screens in the Rothesay's operations room. This recent refit and marginally better radar made them somewhat more suitable for use in the Falklands War and patrols in the South Atlantic, in the immediate aftermath than many of the other Type 12's. In the late 1970's their also serious plans to refit 4 other Rothesays as Towed Array frigates, but Leanders were used instead after the 1981 defence review and Falklands war reassessment.

Service
The Rothesays served throughout the 1960s and 1970s, with HMS Londonderry (F108) converted into a weapons and electronics trials vessel in 1975.The successful performance of the Rothesays, and the ability they showed for sustained operation in rough North Atlantic sea conditions during the 1976 Cod War, combined with the intensification of the Cold War and a more generous naval budget in the late 1970's by the new Prime Minister the former RN Clerk James Callaghan led to a provisional decision to retain the Rothesays through the 1980's with a second long refit. HMS Plymouth, HMS Yarmouth, and HMS Rothesay were given full 2-year refits in 1978-81 with some significant updates of radar. At the beginning of 1982 many of the class had been relegated to the Standby Squadron, likely to be disposed of following the 1981 defence review, with their sister ships likely to follow suit. However, the outbreak of the Falklands War reprieved the class, and HMS Plymouth (F126) and HMS Yarmouth (F101) were despatched with the task force, with Plymouth in particular playing one of the most active roles of any ship. In addition the rest of the class were refitted for service, allowing the losses and damages suffered by the Royal Navy during the conflict to be rapidly made good. HMS Berwick and HMS Falmouth had been retained in a state of high readiness in the standby squadron, in the expectation they would be given a furthur long refit, possibly as Towed Array frigates, their sister HMS Lowestoft had been essentially tested in this role. Berwick in particular still proved useful after its short refit, giving another 3 years operational service, till mid 1985. The class paid off throughout the 1980s, with Rothesay finally paying off in 1988. The demise of the class also saw the withdrawal of the Wasp helicopter, the Leanders having been upgraded to carry the Westland Lynx.

New Zealand ships
The New Zealand Navy ordered two Type 12 ships in February 1957. Hastings was transferred as the Otago while under construction, and Taranaki was ordered directly from the builders. The ships were fitted with Seacat missiles and 12.75 inch torpedo tubes. The New Zealanders considered modernising Taranaki with gas turbines but retired the ships after 1981 when two surplus Leander-class frigates were offered for sale by the British.

South African ships (President class)
Three Type 12 frigates were ordered as part of the Simonstown Naval Agreement. They were identical to the Royal Navy vessels when built but were altered during refits. The three ships were named after presidents of the Boer republics:


 * SAS President Kruger - after Paul Kruger)
 * President Steyn - after Martinus Theunis Steyn
 * President Pretorius - after Andries Pretorius

The modernisation involved installing a hangar and flight deck for a Westland Wasp helicopter, removing the Limbo mortar to form the flight deck, replacing the air search radar and fire control system and adding two triple 12.75 in anti-submarine torpedo tubes.

The ships proved difficult to maintain due to the arms embargo and President Steyn was decommissioned in 1980 to provide spare parts.