However, by the late 1970s it was clear the commercially designed Type 21 had 'insufficient margin' of weight and space when compared to the allowances customary in in-house Royal Navy warship designs for major modernization of the type being applied to the broad-beam Leander frigates, which included the replacement of the subsonic Seacat missiles with anti-missile Seawolf missiles to counter Soviet anti-ship missiles and the fitting of the Type 2016 bow sonar. The Type 21 could be fitted with either the 2016 sonar or Seawolf but not both. Five modernization proposals for the Type 21s were considered by the Royal Navy but rejected by 1979, when it was 'reluctantly' decided not to modernize the class, and it was estimated that they would be laid up by 1988.