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 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 (A/S) escort. As such, a repeat and improved Type 12 design was prepared, known as the Type 12M (Modified), named after the lead ship HMS Rothesay. 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 excellent hull design of the Type 12, that allowed high cruising speed to be maintained in heavy seas, critical to the success of A/S 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.
| General characteristics as built | |
|---|---|
| Displacement: | 2,150 tons / 2,560 tons full load |
| Length: | 370 ft o/a (113 m) |
| Beam: | 41 ft (12 m) |
| Draught: | 17.3 ft (5.3 m) |
| Propulsion: | Y-100 plant; 2 x Babcock and Wilcox boilers, 2 English Electric steam turbines, 30,000 shp 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 |
| Armament: | 1 x twin 4.5in gun Mark 6 |
