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The new design incorporated gas turbines as part of the main propulsion, in the COSAG (combined steam and gas turbine) system which was also used in the 'County' class destroyers. Main propulsion was provided by a 12,000hp steam turbine that could drive the ship at over 20 knots and could be augmented by a G-6 gas turbine (7,500shp) to boost the speed to around 28 knots. The main advantage of this system was that the main steam turbine could be used to give optimum fuel efficiency at normal cruising speeds and the gas turbine could be brought in to give extra power on demand. This meant that less boiler capacity was required with resultant savings on space, manpower and cost. With a gas turbine, the ship could still be powered up and manoeuvred at very short notice while the steam system was still warming up. The disadvantage of the system was that a second funnel was required to carry the gas turbine exhaust, which took up deck space. As a result, the Type 81 was the only frigate design to feature two funnels. The advantages clearly outweighed the disadvantages though and the Royal Navy gained valuable experience in the operation of gas turbines in a wide variety of operational environments and showed that the gas turbine could be reliable enough to run for extended periods. This led to the eventual development of improved models, which were installed as the only propulsion system on later classes.
The new ship also incorporated guided missiles as part of the main armament for the first time. Space was provided for a quadruple Seacat launcher and its associated GWS21 control system. The launchers were positioned either side of the foremast while the directors were on platforms either side of the second funnel. The missile was steered by radio command guidance and the target could be tracked visually or by the Type 262 radar in the director. Due to delays in the development and procurement of the Seacat, all the ships except Zulu had single 40mm AA guns installed in place of the launchers and were gradually refitted as the equipment became available. In addition to this the vessels were also designed with facilities to carry and operate a helicopter as part of the ship's equipment, which, due to the space, meant that the ship could only be provided with a single Limbo mortar.
The Type 81 had a displacement of 2,300 tons as standard, and 2,700 tons if fully loaded. It was 360 feet long, had a beam of 42.5 feet and a draught of 17.5 feet. The ship had a completely flush deck with considerable sheer with the superstructure block extending the entire width of the ship, supporting the bridge and mast. Both funnels were set aft and raked back slightly with the small hanger and flightdeck being towards the very rear of the ship.
The Type 81 had a main gun armament of two single 4.5in guns (Mk V mounting), one being just forward of the main bridge (that had three 2in rocket flare launchers mounted), the other on the quarterdeck. These had come from scrapped 'C' group destroyers but had been modified to improve sighting and loading arrangements before they were fitted to the new ships. They had a maximum range of around 19km, and while the 50-degree elevation would only give them limited effectiveness against aircraft, they were really meant to engage surface and land targets. Fire control was by means of a MRS3 director that was mounted behind and just above the main bridge and incorporated a Type 903 radar for tracking targets. The ship also had a Type 965 radar fitted with a AKE1 'Bedstead' aerial, a Type 993 radar with a 'Cheese' aerial and a Type 978 navigation radar on a small platform projecting forward from the main mast. The Seacat system provided a simple but effective close-range air defence system that was subsequently fitted to almost all British and some foreign warships. Two four missile launchers were fitted on either beam and had a maximum range of 4.75km. Anti-submarine weapons consisted of a single Limbo mortar and a Wasp helicopter, and while the inclusion of six torpedo tubes was dropped, the ship had a comprehensive sonar suite with Type 177, 170 and 162 sonars being fitted.
The ships were a giant step forward in terms of crew comfort and facilities. It was the first ship to have cafeteria-like messing facilities and bunk sleeping. Full air conditioning for all accommodation, working and operational areas was provided which meant that the class could operate in a wide variety of environments without being specially modified. A detachment of Royal Marines was carried with their weapons and equipment, the concept being first tried out with HMS Loch Killisport and having proved a success, was adopted on the Tribal and most other frigates as well.
The class was named after the 'Tribal' class destroyers that had served with distinction in the Second World War. These destroyers had represented a major change in design philosophy and so it was thought fitting that the new class of frigates was named after them. The lead ship of the class, Ashanti, was commissioned in late 1961 and put through extensive trials to test the new propulsion system and to develop operation procedures for using light helicopters on frigates. The last vessel in the class was Zulu, which was completed in April 1964. As a class, the ships saw service all around the world, with considerable time spent in the Persian Gulf, Middle East and West Indies, due to their high level of accommodation and air conditioning.
Modifications were limited - those vessels that initially had 40mm anti-aircraft guns had them replaced by the Seacat. All ships had two single 20mm guns mounted on each beam just forward of the bridge that could be used in peacetime or low intensity conflict situations where the use of the main guns or Seacat missiles might be inappropriate. This was a lesson learnt in the Indonesian Confederation in 1962 - 3 where many patrolling frigates had found that they had no effective armament to engage small boats and fishing vessels used for gun-running. Also, two Knebworth / Corvus multiple rocket launchers (that fired chaff to confuse incoming radar-guided missiles) were mounted, one each side of the bridge from 1970 onwards. Ashanti (1968) and Gurkha (1969) were fitted with the new Type 199 variable depth sonar, which was installed on the quarterdeck.
These ships were very useful for peacetime patrolling and low intensity conflict operations (what today would be called Peace Support Operations) as well as 'showing-the-flag' visits. Their limited armament and low speed made them unsuitable to be combined with the remainder of the fleet in Task Force situations and mostly operated on detached duty. With the introduction of new frigate classes and the run down in naval strength, they were relegated to first the Standby Squadron and then listed for ultimate disposal in the 1981 Defence Review, Ashanti having been mothballed in 1979 and Tartar, the last operational ship of the class, being decommissioned in December 1980. Vosper Ship Repairers actually proposed a modernisation programme, with a view to selling them abroad where the two 4.5in guns would be replaced by a single automatic 76mm gun mounted forward. The Mk 10 mortar and existing hangar and flightdeck facilities would be removed and new facilities installed that extended to the stern so the ship could operate a Lynx helicopter. A large streamlined funnel would replace the two separate ones and a new Fire Control system installed. Although there were rumours that Venezuela was interested in buying some of the class, the deal never materialised and it's a shame that the modernisation could not have gone forward with the ships being retained in Royal Navy service as the ships had been relegated to disposal well before the end of their useful lives. The Falklands conflict saw three of the ships (Tartar, Gurkha and Zulu) being recommissioned into service to cover for combat losses and ships being laid up due to battle damage. This showed the value of keeping a number of ships in reserve so that they can be activated should the need arise. The remaining four 'Tribal' class ships were not recommissioned and were stripped of any serviceable equipment to keep the other three going. By 1987, all four had been disposed of, Mohawk being scrapped in 1982, while Eskimo, Nubian and Ashanti were all sunk as targets in 1986, 1987 and 1988 respectively. The other three had another two years of service, after which they were bought by Indonesia, refitted by Vosper Thornycroft at their Woolston yard and commissioned into the Indonesian Navy as Martha Kristina Tiyahahu (Zulu, 1985), Wilhelmus Zakarias Yohannes (Gurkha, 1985) and Hasanuddin (Tartar, 1986).
|Ashanti||15 January 1958||9 March 1959||23 November 1962|
|Eskimo||22 October 1958||20 March 1960||21 February 1963|
|Gurkha||3 November 1958||11 July 1960||13 February 1963|
|Mohawk||23 December 1960||5 April 1962||29 November 1963|
|Nubian||6 September 1959||6 September 1960||9 October 1962|
|Tartar||22 October 1959||19 Sept 1960||26 February 1962|
|Zulu||13 December 1960||3 July 1962||17 April 1964|
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