Corvettes to sail smartly: nearly half a century ago the major navies' last corvettes were being towed ignominiously to the scrap yards. But over the past two decades there has been a renaissance in this category; not just among Third World navies but also some of the major naval powers, indeed even the Royal Navy has shown interest in this type of warship.

The modern corvette owes its origins to a British requirement for what Churchill referred to as a 'cheap and nasty' anti-submarine vessel. Designed to operate over the continental shelf the corvettes evolved into small, general-purpose escort vessels, but even the improved designs were slow, had range restrictions and limited capacity for antisubmarine sensors and weapons so in their original role they were gradually replaced by frigates. These limitations accelerated their post-war demise in most major navies, especially their poor anti-submarine warfare (ASW) capabilities as the Cold War saw the growing threat from submarines with high underwater speeds.

However, the Soviet Union did not regard these limitations, especially the restricted anti-air warfare (AAW) capability, as relevant because their ships would operate behind the shield of land-based air power. Corvettes were produced in considerable numbers to augment fast attack craft and the most notable vessels were the Pauk, Nanuchka and Tarantul classes. The Tarantuls displace 455 tonnes, are 56 metres long and armed with four surface-to-surface missiles (usually SS-N-2 'Styx'), a 76 mm gun and two AK 630 close-in-weapon systems. Unusually, they are powered by gas turbines, and in addition to an air/surface search radar and a fire control radar they have variable-depth sonar but no antisubmarine weapons.

Many smaller navies had similar operational scenarios and acquired Russian or Russian-designed corvettes, while India built the Tarantul I as the Veer class and improved versions as the Khukri and Kora classes. During the 1970s and 1980s Ecuador, Italy, South Korea, Portugal, Iraq and Saudi Arabia all acquired corvettes, many from Fincantieri. The Iraqi Assads would eventually be sold to Malaysia as the Laksamana class. These ships differed from the Russian corvettes in having a better ASW capability in terms of hull-mounted sonar and lightweight anti-submarine torpedoes. It might well be argued that Washington also adopted the corvette philosophy during the 1960s, when the US Coast Guard's Hamilton/Hero high-endurance cutters were equipped with sonars, surface-to-surface missile systems and torpedo tubes to augment the US Navy's escort forces, although the missiles and ASW equipment were removed with the end of the Cold War.

The Western renaissance began in the late 1980s and early 1990s on the back of the boom for fast attack craft. After an Egyptian Osa class vessel sank the Israeli destroyer Eilat in 1967 there was a surge in orders for fast patrol boats equipped with surface-to-surface missiles, which many smaller navies regarded like the Colt revolver as an equaliser with the major navies. The potential of fast attack craft both for anti-surface warfare (ASuW) and land attack was demonstrated in the early 1970s, but in the following decade the limitations of the concept also became apparent.

Semantics

Like the British battle cruisers in 1916 the fast attack craft proved vulnerable to plunging fire, in this case missiles delivered by aircraft, and US naval air power severely punished both Libyan and Iranian vessels. The lesson was driven home in 1991 when Allied air power massacred Iraqi fast attack craft (some of them former Kuwaiti vessels) making a sortie down the Saudi Arabian coast. The range of fast attack craft search radar was restricted by the low height at which the antenna was carried, depriving them of early warning while their air-defence capability was further eroded by the absence of anything more than man-portable missiles. The small size of the fast attack craft, less than 55 metres long and with a displacement of 500 tonnes or less, made them especially vulnerable to missile strikes--those that did survive were fit only for the scrap yard.

Semantically the problem was being addressed in the 1970s. The Lurssen 62 design, which was 63 metres long with a displacement of some 630 tonnes, was described as a fast attack craft by Bahrain (A1 Manama class) but as a corvette by both Singapore (Victory class) and the United Arab Emirates (Muray Jib class). The Gulf navy ships were given a helicopter landing capability but, about the same time, there was also confusion with the Howaldtswerke FS 1500 design. This ship was between 97 and 99 metres long with a displacement of between 1850 to 2100 tonnes and was described as a frigate by Colombia (Almirante Padilla class) and a corvette by Malaysia (Kasturi class).

The change of heart was most dramatically demonstrated in Sweden, which disposed of its major surface combatants and replaced them with fast attack craft and almost immediately began to suffer a series of underwater incursions. This helped underline the need for larger warships and, in 1981, led to what were essentially renamed fast attack craft, the Stockholm class corvettes being improved Spica I, with Codag (COmbined Diesel And Gas turbine) propulsion and a quantum leap in anti-submarine capability. Within four years Sweden ordered four Goteborg class corvettes with Codad (Combined Diesel) and water-jet propulsion to replace the Spica Is. These ships have a Celsius Tech (now SaabTech) 9LV Mk 3 combat management system, Saab RBS 15 surface-to-surface missiles, Bofors (now BAE Systems Bofors) 57 mm and 40 mm guns and a Thales Underwater Systems Salmon variable-depth and a Simrad SA 960 hull-mounted sonar. However, their offensive anti-submarine armament was weak, designed to 'tap' submarines rather than 'boot' them and there was no significant air-defence capability.

The Eilat Syndrome

Israel has followed the same path from major warship to fast attack craft to corvette, partly spurred on by the Eilat incident, which has led the trend towards enhanced AAW capability in corvettes. In the 1990s the Israelis built under licence an Ingalls/John J. McMullen Associates design with Foreign Military Sales funding as the Eilat or Sa'ar 5 class. This 1295tonne Codog ship with traditional shafts, which may be about to replace its Elta EL/M-2218S radar with the IAI Elta MF-Star active array sensor, has an Elbit NTCCS combat management system, Boeing (formerly McDonnell Douglas) Harpoon surface-to-surface missiles, and was the first to feature an effective surface-to-air missile system in the form of the Israel Aerospace Industries Barak 1. This was one of the first corvette 'stealth' designs with shaping and radar absorbent material to combat radars while the acoustic signature is reduced by resilient mountings for machinery together with a Prairie Masker bubble system. This and the increased mass of the design demonstrated the advantages of the whole corvette concept in July 2006, when the INS Hanit was hit by a C-802 anti-ship missile off Lebanon. Despite the fact the ship had its main search radar and close-in weapon system switched off the missile struck the corvette's stern and, while killing four crew, it inflicted limited damage and the ship quickly returned to front-line duties.

The trend was underlined by the 1992 sale of the Vigilance design to Oman by Vosper Thornycroft (Now VT Shipbuilding). The Codad-powered Qahir class is only 83.7 metres long with a displacement of 1450 tonnes but represents a quantum leap in capability. The size will help to contain damage and also means the prime sensor, the Thales Nederland MW 08 air/surface surveillance radar, has a much wider range to detect incoming threats. A Thales Nederland Tacticos combat management system increases capability by integrating the traditional ASuW weapons system. MBDA Exocet surface-to-surface missiles and Oto Melara 76 mm Super Rapid gun with the other elements of the weapon system. An AAW capability is due to a Thales Crotale surface-to-air missile system supported by Thales Nederland Sting directors. There is also an ASW capability through a Thales Atas active towed array sonar and a platform for a medium-weight (five-tonne) helicopter.

The United Arab Emirates has adopted the CMN BR 67 Codad design to meet its Bayunah requirement, with the first-of-class being built by CMN in Cherbourg and the remainder by Abu Dhabi Shipbuilding. These will be 630-tonne ships with a Selex Sistemi Integrati IPN-S combat management system, NA-25 weapon control directors, Ericsson Sea Giraffe radar and Sagem Eoms electro-optical director, a Raytheon Evolved SeaSparrow Missile surface-to-air missile system but no anti-submarine capability. Interestingly, their surface-to-surface weapons will be the MBDA Exocet Block III, which have a limited land-attack role.

By contrast the 1650-tonne Sigma corvettes, also Codad-powered, being built by Royal Schelde will have a Thales Kingclip hull-mounted sonar and torpedo armament. Although incorporating stealth design features this is more of a traditional corvette with MBDA Tetral multiple launchers for Mistral man-portable surface-to-air weapons and Exocet Block II anti-ship missiles. The first, KRI Diponegoro, was launched on September 16. Indonesia has a requirement for four ships.The three corvettes built by BAE Systems for neighbouring Brunei are more versatile, although also Codad-powered. Equipped with the company's Nautis combat management system, AWS-9 search radar and augmented by an Ultra 2500 electro-optical director, this class also has Exocet Block II missiles. It also has Seawolf VL missiles and an antisubmarine system based upon a Thales Underwater Systems 4130 sonar and lightweight torpedoes. There is currently (as of November 2006) a dispute between the two parties over these vessels, with a legal resolution anticipated by the end of 2006. Even if Brunei decides not to accept them there is no doubt BAE Systems will readily find alternative purchasers.

Demand on the Up

The demand for corvettes is growing, with requirements for about 65 hulls from Bangladesh, Bulgaria, Kuwait, Poland, Romania, Saudi Arabia, Turkey and Vietnam. The DCN Gowind design was reported as having been selected by Bulgaria. Brazil is the only Latin American country building a corvette, the much delayed Barroso laid down in 1994 and scheduled for completion in 2008, while Poland also has a much delayed programme building a 2035-tonne ThyssenKrupp Marine (Blohm & Voss) Meko 100, which will feature RBS 15 surface-to-surface and evolved Sea Sparrow surface-to-air missile systems. Known as Gawron II (and sometimes referred to as a frigate class) the first-of-class was laid down in 2001 but the Poles have stated that it will not be launched until 2010. Although both vessels feature combined gas turbine and diesel propulsion the fundamental problem is funding rather than technology.

Somewhat faster turn-around times may be expected from other countries with corvette requirements. India has begun building four 2500 tonne diesel-powered Project 28 vessels, with the first scheduled for completion in 2009. They will have a mix of British, Israeli, Italian, Russian and indigenous equipment. Turkey is working on its Milli Gem (Milgem) programme with the first of eleven ships, the TCG Heybeliada, to be launched in 2007, although key decisions on sensors have still to be made. These 2500-tonne ships, powered by gas turbines and diesels, will be general-purpose vessels with air defence provided by the Raytheon Rolling Airframe Missile.

Perhaps the most radical corvette design currently being produced is that of Sweden's Visby class. These must be regarded as the stealthiest ships in the world, with a shaped hull of fibre-reinforced plastic coated with radar-absorbent material. The gun and the radar director are unique in that they are also shaped, the gun merges into the gun housing and the helicopter can descend from the flight deck into the hanger. The Codog-water jet propulsion of the G6teborgs was copied, together with the limited air-defence capability, but these 620-tonners are unique in having a mine countermeasures role using Computing Devices Canada Hydra sonar and an Atlas Sea Fox mine surveillance/destruction system. The ships are also capable of laying mines. The first-of-class was commissioned in May 2006.

Corvette or Frigate?

Further along the Baltic, Russia was reported to be building the Project 20380 (Steregushchiy) class as a replacement to the Tarantul, but these 1900-tonne ships are also referred to as frigates. The first-of-class began trials during the autumn of 2006, by which time the fourth had been laid down as part of a programme of nine. This illustrates the problems of distinguishing between corvettes and light frigates, with the problem further complicated by plans for up to nine Project 12300 (Scorpion) class corvettes. It is worth noting that under an agreement signed in 2006 Russia will refurbish and refit the second of Algeria's Nanuchka II class corvettes.

Germany is building its first corvettes for 40 years; six of the Braunschweig (K 130) class. These 1662-tonne, diesel-powered, ships have TRS-3D radar, a Tacticos combat management system, including a Thales Nederland Mirador electro-optical director, RBS-15 and Ram missiles and an Oto Melara 76 mm Super Rapid gun and, like many corvettes, will incorporate the Rheinmetall Mass countermeasures system. These ships are regarded as successors to the fast attack craft, which can no longer meet the growing demand for autonomous, out-of-area deployment.

Such demands may influence even a major player, such as the British Royal Navy. A successor to the Duke (Type 23) and Broadsword (Type 22) class frigates has been sought for about a decade under a number of names, of which the best known is the Future Surface Combatant. A proposed solution for part of this requirement is a corvette-type ship, which would (theoretically) be cheaper but provide a vessel with reasonable combat effectiveness. Given the plans for the Visby, the British Ministry of Defence is also considering giving such a surface combatant a mine countermeasure capability.

The question of semantics bedevils the issue of corvettes and is illustrated by Malaysia's requirement for a New Generation Patrol Vessel. Ostensibly an Offshore Patrol Vessel (OPV) the ship selected to meet the requirement was the ThyssenKrupp Meko A 100 but the patrol vessel includes an Atlas Cosys combat management system, Eads TRS-3D search radar, an electro-optical director and an Oto melara 76 mm Super Rapid gun. The reason for the Cosys is that the ship is designed for but not fitted with a sonar and surface-to-surface and surface-to-air missiles. Two were built and commissioned by mid-2006, four were being built in Malaysia but the programme appeared to grind to a halt by the end of 2006.

Oman and Venezuela both have similar requirements for 'OPVs'. VT Shipbuilding is to meet the former's Project Khareef requirement with three 2500-tonne ships which will have a combat management system, surface-to-surface and surface-to-air missiles (MBDA's VL Mica). Navantia will meet Venezuela's Patrullero Oceanico de Vigilancia de la Zee (EEZ Ocean Patrol Ships) requirement with a 2300-tonne ship carrying an Oto Melara 76 mm gun, a helicopter and missiles. Steel for the first ship was cut in September 2006. Both contracts should see vessels delivered around the end of the decade.