Like maternal hens, Navy blimps hover over a sea-borne convoy, alert to any danger on the horizon or beneath the surface. Airships are capable of speeds of 60 knots or more, yet can ride indefinitely over danger spots. Their cargo of depth bombs makes them a deadly danger to the submarine. As convoy escorts, the lighter-than-air branch of the Navy has played its part in reopening coastal shipping lanes. (http://www.naval-airships.org/page-770913)