A blue-water navy implies force protection from sub-surface, surface and airborne threats and a sustainable logistic reach, allowing a persistent presence at long range. A hallmark of a true blue-water navy is the ability to conduct replenishment at sea (RAS), and the commissioning of underway replenishment ships is a strong sign of a navy's blue-water ambitions. While a blue-water navy can project sea control power into another nation's littoral, it remains susceptible to threats from less capable forces (asymmetric warfare). Maintenance and logistics at range have high costs, and there might be a saturation advantage over a deployed force through the use of land-based air or surface-to-surface missile assets, diesel-electric submarines, or asymmetric tactics such as Fast Inshore Attack Craft. An example of this vulnerability was the October 2000 USS "Cole" bombing in Aden.