Frigates fulfill a Protection of Shipping (POS) mission as Anti-Submarine Warfare (ASW) combatants for amphibious expeditionary forces, underway replenishment groups and merchant convoys. The guided missile frigates (FFG) bring a short range anti-air warfare (AAW) capability (provided by their Phalanx Close-In Weapon System) to the frigate mission, but they have some limitations. Designed as cost efficient surface combatants, they lack the multi-mission capability necessary for modern surface combatants faced with multiple, high-technology threats.