The Baleares class are a group of five frigates built for the Spanish navy in the 1970s. The ships are a modified version of the American Knox class frigates. The key differences are the replacement of the Sea Sparrow PDMS and ASW helicopter facilities by Standard SAM and associated radars. They received a SPS-52B 3D search radar and one SPG-51 illuminator for the Standard SM-1 medium range SAM, fired from a Mk22 16-round single arm launcher. The SQS-26 long range LF sonar was replaced by a SQS-23G MF sonar, while two Mk25 tubes for Mk37 torpedoes were mounted in the transom. The SQS-35 variable depth sonar was maintained.