Baleares-class frigate

The Baleares class were a group of five frigates built for the Spanish Navy in the late 1960s and 1970s. The ships were a modified version of the American Knox-class frigates. The key differences are the replacement of helicopter facilities by a medium-range surface-to-air missile system and associated radars. Constructed between 1968 and 1976, the Baleares class began entering service in 1973 and formed the 31 Escort Squadron, based at Ferrol. The five ships were upgraded several times during their service lives. The ships were retired beginning in the mid-2000s and replaced by the Álvaro de Bazán-class frigates on a one-to-one basis.

Background
In the 1960s, Spain sought to update its fleet of warships. The government entered into negotiations with the United Kingdom for the acquisition of four Leander-class frigates. However, the negotiations failed as questions were raised in the United Kingdom over dealing with the unpopular Spanish government. Instead, the Spanish government turned to the United States and on 17 November 1964 an agreement acquire five Knox-class frigates was signed. On 31 March 1966, a technical support agreement was reached between the two nations. As part of the agreement, the hulls and machinery were to be constructed in Spain at Ferrol while the weapons and sensors would come from the United States. The superstructures were to be built at Alicante, Spain and the boilers, distilling machinery and propellers at Cádiz.

Design and description
Though copies of the American Knox class, the Baleares class was a modified design. The Spanish frigates removed the aft flight deck and helicopters along with the short-range Sea Sparrow missile defence system and replaced them with the medium-range Standard surface-to-air missile (SAM) system. The frigates of the Baleares class had an initial standard displacement of 3015 MT and a full load displacement of 4177 MT. They measured 126.5 m long between perpendiculars and 133.5 m long overall with a beam of 14.3 m and a maximum draught of 7.5 m over the sonar. The ships would go through a series of modifications throughout their service, with their standard displacement increasing to 3350 MT and their draught increasing to 7.8 m over the sonar.

The Baleares class were equipped with one Westinghouse geared turbine turning one shaft creating 35000 shp. It was powered by steam from by two Combustion Engineering V2M boilers. The boilers had a working pressure of 84.4 kg/cm2 at 510 C. This gave the Baleares class a maximum speed of 28 kn. They had capacity for 750 MT of fuel oil giving them a range of 4500 nmi at 20 kn. They had a complement of 256 including 15 officers.

The frigates were initially armed with one 5 in/54-calibre Mk 42 naval gun, the Standard SM1-MR SAM system with a Mark 22 launcher and 16 missiles and the Mark 112 octuple RUR-5 ASROC anti-submarine warfare system using Mark 46 torpedoes with eight reloads. The frigates also had four 12.75 in torpedo tubes fitted internally into the port and starboard of the aft superstructure and inclined at 45° for Mark 44 torpedoes and two 21 in torpedo tubes fitted internally at the stern for Mark 37 torpedoes. The ships stored 41 torpedoes total. The Baleares class underwent a two stage mid-life modernisation between 1985 and 1991 which involved the addition of four Harpoon surface-to-surface missiles in the first stage and two 20 mm Meroka CIWS gun systems in the second stage. They also had their stern torpedo tubes removed to accommodate the variable depth sonar installation.

The frigates initially fitted AN/SPS-52A air search and AN/SPG-51C gun fire control radars along with AN/SQS-23 hull-mounted and AN/SQS-35A variable depth towed sonars. During the first stage modernisation, the ships were given AN/SPS-10F surface search radar and the AN/SPG-53 Mark 68 gun fire control system. The ships were also given upgraded fire control where the Mark 74 system used the Mark 73 director and the SPG-51C radar along with the Mark 68 director with the SPG-53 radar to control two Standard missiles simultaneously. The Mark 68 could also be used to control the main gun. Additionally, the frigates received SRN-15A, TACAN, the TRITAN-1 combat data system and NATO Link 11. During the second stage, the Baleares class received the RAN-12L/X air search radar for the Meroka CIWS system and replaced the original SQS-23 sonar with the DE1160LF sonar. They also saw their electronic warfare suite improved with the addition Mark 36 SBROC decoy launchers.