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Rothesay-class frigate

HMS Plymouth underway.jpg
Class overview
Name: Rothesay class
Operators:
Preceded by: Type 12 Whitby
Succeeded by: Type 12I Leander
Completed: 21
Lost: 5 (as targets) + 1 (accident)
Retired: 4
Preserved: 1
General characteristics as built
Type: Frigate
Displacement:
  • 2,150 long tons (2,180 t) standard
  • 2,560 long tons (2,600 t) full load
Length: 370 ft (110 m) o/a
Beam: 41 ft (12 m)
Draught: 17.3 ft (5.3 m)
Propulsion: Y-100 plant; 2 × Babcock & Wilcox boilers, 2 English Electric steam turbines, 30,000 shp (22,000 kW) on 2 shafts
Speed: 30 knots (56 km/h)
Range: 400 tons oil fuel; 5,200 nautical miles (9,630 km) at 12 knots (22 km/h)
Complement: 152
Sensors and
processing systems:
  • Radar Type 293Q target indication
  • Radar Type 277Q height finding
  • Radar Type 275 fire control on director Mark 6M
  • Radar Type 974 navigation
  • Type 1010 Cossor Mark 10 IFF
  • Sonar Type 174 search
  • Sonar Type 162 target classification
  • Sonar Type 170 attack
Armament:
General characteristics (as modified)
Displacement:
  • 2,380 long tons (2,420 t)
  • 2,800 long tons (2,800 t) full load
Complement: 235
Sensors and
processing systems:
  • Radar Type 993 target indication
  • Radar Type 903 fire control on director MRS3
  • Radar Type 978 navigation
  • Type 1010 Cossor Mark 10 IFF
  • Sonar Type 177 search
  • Sonar Type 162 target classification
  • Sonar Type 170 attack
Armament:
Aircraft carried: 1 × Westland Wasp HAS.1 MATCH helicopter
Notes: Other characteristics as per above

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, were designed as first-rate ocean-going convoy escorts in the 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 called 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.

The Type 12M retained the 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 at the time the first ships in class were completed, and either a twin Bofors 40 mm gun in a STAAG (Stabilised Tachymetric Anti-Aircraft Gun) mounting (Rothesay) or a single Bofors 40 mm gun on a Mk.7 mount was shipped in lieu. The arrangement of the torpedo tubes was also altered in the new design, with four 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 ship 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.


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