 Improvements in surface-to-air missiles (e.g., the Eurosam Aster 15) allow modern guided-missile frigates to form the core of many modern navies and to be used as a fleet defence platform, without the need for specialised anti-air warfare frigates.The Royal Navy Type 61 "Salisbury" class were "air direction" frigates equipped to track aircraft.To this end they had reduced armament compared to the Type 41 "Leopard"-class air-defence frigates built on the same hull.