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The first steps towards technological self-sufficiency in modern shipbuilding was taken in the 1970s with the Descubierta-class corvettes. When first introduced ships of the "Descubierta" Class were the most modern in the Spanish Navy. They began to be developed in 1972, when the Spanish naval command awarded a contract to the Bazan shipbuilding company for drawing up the design of a frigate satisfying the following specifications: full load displacement 1,200-1,500 tons; full speed of at least 25 knots and cruising speed of 18 knots, with a range of 4,000 nm at cruising speed; armament: antiship and surface-to-air missiles, medium and small caliber guns, and antisubmarine torpedoes; shipboard systems and equipment must be of domestic production or be made in Spain under license.

The new ship was developed on the basis of the frigate "Joao Coutinho" of the Portuguese Navy, developed by the West German firm of Blohm und Voss. Three ships of this series were built during 1970-1971 by the Bazan company. In mid-1973 the company submitted four versions of a conceptual design which differed from each other primarily by the make-up of armament. After studying them, naval specialists decided in June 1973 for technical development of a design and then construction of a series of four frigates.

The lead ship was named "Descubierta". She was laid down in November 1974 and became operational four years later. An additional contract was awarded in May 1976 for building one more series of four ships. The construction of all eight frigates was complete by mid-1983. Six of them became part of the Spanish Navy and two were sold to Egypt. Two F-30 "Descubierta" frigates purchased from the Spanish Royal Navy whenthey were under construction. They are the "Suez" (formerly) "Cehtinela" and the "Abu Zir" (formerly "Serviola"). They were delivered in May and July 1984, respectively.

The frigate has a flush-deck hull with a slight flare of the bow frames, and a cruiser stern. The longitudinal framing is made of high-strength steel, which allowed a reduction of more than 15 tons in the expenditure of metal, and the transverse framing is made of low-carbon steel (the carbon content is up to 0.2 percent). The ship has two decks (one continuous and the other is interrupted in the area of the engine rooms), one forward platform deck, a double bottom and ten watertight bulkheads. Liquid cargoes are accommodated in the double-bottom space. The design provides that the ship must remain afloat even with two adjacent watertight compartments flooded.

The bow and stern superstructures are made basically of aluminum-magnesium alloy. The former accommodates a flying bridge and a massive pyramidal foremast with radar antennas. A Y-shaped smoke funnel rises in the forward part of the latter superstructure and behind it a small pyramidal mainmast with a radar antenna. A combat information center is accommodated on the first tier of the three-tiered bow superstructure. A post for transferring cargoes at sea is installed on each side.

A quiet propeller is used on the ship to reduce noise, an auxiliary gasturbine generator is fitted on the upper deck, and all main and auxiliary diesels are installed on sound-insulating mounts. The frigate uses a twin-shaft propulsion plant which includes four high-rpm diesels. In the opinion of foreign specialists, this solution facilitates its repair inasmuch as the diesels are compact and are relatively light in weight, and it increases their service life since partial operation at cruising speed is planned (usually one diesel per shaft). The output of each 16-cylinder turbo-supercharged diesel is ~,750 or 4,150 hp depending on rpm (1,480 and 1,530 rpm respectively). They can develop 4,500 hp (1,575 rpm) for a short time (2 hours). The diesels operate in pairs through a reduction gear on two five-bladed controllable pitch propellers 3 m in diameter (250 rpm).

The main propulsion plant is accommodated in two rooms, where there are also two diesel generators each, each with a maximum output of 370 kw (the diesel output is 520 hp). The auxiliary gas-turbine generator (it is for an emergency and is intended for operation at quiet speeds) has an output of 450 kw. There is 100 percent reserve of electrical power, which allows subsequent modernization of the ship without requiring additional refitting of an electric generating plant. There is a degaussing system with coils regulated automatically or manually.

"Descubierta" Class frigates are armed with the NATO-Sea Sparrow surface-to-air missile [SAM] system eight-cell launcher (on the first four ships), accommodated aft of the stern superstructure. The other ships are armed with the Albatros SAM system. The first system uses the RIM-7H Sea Sparrow single-stage SAM with folding lateral fins, a semiactive homing system and supersonic speed. Its launch weight is 200 kg, its length is 3.66 m and its flight range is 18 km. The system weighs 12 tons overall. The second system consists of the single-stage Aspid SAM with semiactive homing system (a flight range of 20 km, launch weight of 220 kg and length of 3.7 m). The SAM as well as the gun fire control system includes the WM 22/41 or WM 25 radar in the 3.3 cm band. The first is a combination antenna (it includes two two-dimensional radars). The radar antenna system, which consists of two antennas, is accommodated on the foremast beneath a spherical radiotransparent cover. It permits simultaneous tracking of air and waterborne targets and control of fire against them.

The ship's bow accommodates a compact OTO Melara 76-mm multipurpose turret gun mount. Its design makes wide use of aluminum alloys and the turret is made of fiberglas. Ammunition supply and gun loading are automated. Rounds prepared for firing are accommodated in a drum magazine in two rows. The gun mount's maximum rate of fire is 85 rounds per minute, maximum altitude is 11,800 m, maximum horizontal range of fire is 16 km, and the gun mount weighs 7.5 tons overall.

The stern superstructure accommodates two Breda Type 564 40-mm single-barrel automatic gun mounts made in Italy on the basis of the Swedish Bofors 40-mm gun mounts. The gun mount's maximum altitude is 8,700 m, horizontal range of fire is 12.5 km, rate of fire is 300 rounds per minute, and the gun mount weighs 3.3 tons overall. An automatic ammunition feed system permits firing 144 rounds accommodated in a three-row drum magazine with no personnel present. The ship additionally has two French electro-optical systems for controlling the fire of these gun mounts, and if necessary they also can be used to control the fire of other weapon systems.

The frigate is armed with two Mk 32 324-mm triple torpedo tubes accommodated on the sides of the stern superstructure for antisubmarine warfare. They are employed for firing small Mk 46 torpedoes. A Bofors 357-mm twin-tube rocket launcher (with an overall weight of 3.8 tons and a rate of fire of two antisubmarine rockets every 45 seconds) is installed on the superstructure forward of the flying bridge. The flight range of the Erika antisubmarine rocket is 600-1,600 m and that of the Nelli is 1,500-3,600 m depending on the motor power and they submerge to a depth of 140-200 m respectively. Target designations are issued for antisubmarine weapons using the DE 1160 built-in sonar (the analog of the American AN/SQS-56 sonar) coupled with the AN/UYK-16 computer and are displayed on the screens of the control consoles. The plans were to install the DE 1164 sonar system consisting of the DE 1160B sonar and a passive towed station aboard ships of the second subgroup.

In addition, the ship's electronics included: DA OS/2 air/surface early warning radar with parabolic antenna accommodated on the mainmast. The radar can be used for target classification and fire control. Airborne targets can be detected at a range of 140 km. Accommodated above the antenna is an IFF system, the ZW 06 radar for detecting waterborne targets and a navigation radar with parabolic antenna (2.9x1.2 m) on the foremast, radio direction finder, fathometer, Beta REB [electronic warfare] system and communications equipment. The ship has the SEWACO [Sensor, Weapon and Command System] command coordination system. Three consoles (two double ones) are installed on the bridge for control of the propulsion plant and steering arrangement; control of the navigation radar and navigation situation display; and control of communications systems.

Recognizing that the armament of "Descubierta" Class frigates did not meet modern requirements, especially with respect to combating surface ships, the naval leadership, later fitted them with two Harpoon four-cell antiship missile launchers.

In the 2004 timeframe four of these ships were reclassified from Frigate to Patrol Vessel. The flagship of the Descubierta class, the Descubierta, was retired from service in 2009. Descubierta's sisters (Diana, Infanta Elena, Infanta Cristina, Cazadora and Vencedora) remain in active service (Diana now serves as a large mine countermeasures command ship; the other Descubiertas serve as patrol vessels).

The main mission of the patrol vessel is that of maritime surveillance. Within this field, the entrusted missions can be diverse, as protection of the environment, fisheries surveillance, the fight against immigration and drug trafficking, as well as maritime traffic control. In recent times, and given the increase in piracy taking place in various parts of Africa, they also happened to carry out anti-piracy missions.

It is reported that when the Descubiertas were converted from front-line naval combatants towards becoming large patrol vessels, the Spaniards stripped them of their heavy arms- the Harpoon SSMs, the Sea Sparrow SAMs, and the ASW torpedoes and associated equipment. as patrol vessels, they were mainly armed by the 76mm Oto Melara gun and smaller caliber guns. The 552-A, the model was presented to the Spanish Navy in 1980 and the latter expressed great satisfaction even to the point that there was talk of the possibility of this ship becoming the replacement of the two "Descubierta" type corvettes sold to Egypt. The 552-A became known as the stretched version of the "Descubierta" given that it followed the natural evolution of the stupendous Spanish corvette in its 2,100-ton model.

The "Sagitario," designated as project 552-D, was designed in its final form by Bazan in 1983, involving an addition of 400 tons. The "Sagitario" had the extensive antiaircraft and antisubmarine capability of the "Descubierta"-type corvettes with weaponry similar to the "559" frigate even though it is naturally smaller. Its crew would total 165 officers and men and its speed would exceed 28 knots an hour even though the new "D" class seemed to have even greater speed. It would carry a single helicopter.

In 1983 the Philippines had an interest in the 2,500-ton frigate "Sagitario" project designed by Bazan in Spain. The three units of potential interest to the Philippines may be increased in number since Indonesia also wished to examine this corvette.

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