Many of these ships were retired in the 1990s whether they received the full NTU modification or not; most of these warships built in the 1960s-1970s had high operational costs and manpower requirements (especially those which were nuclear-powered), compared to newer Aegis warships.
Many of these ships from the 1960s-1970s, which were either nuclear-powered or not, were decommissioned in the 1990s due to high operational costs and manpower demands. Newer Aegis warships offered a more cost-effective solution compared to their older counterparts.