A whirring comes across the sky. From 20,000 feet above the Mexican border or Afghanistan’s Korengal Valley, a vehicle as long as the Chrysler building is tall drifts into the stratosphere. It looms like a cloud and stays put for 21 days, scanning for body heat below. These blimps are lighter than air, fuel-efficient and quiet—which is why they could become the military’s go-to vehicles for surveillance and transport.

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Sky HQ

Last summer, the U.S. military awarded Northrop Grumman a $517-million contract for a Long Endurance Multi-Intelligence Vehicle (LEMV). The 300-foot-long aircraft gets about 40 percent of its lift from its hull’s aerodynamic shape. It can stay aloft for three weeks at a time running surveillance. Northrop says the LEMV will be ready for action by the beginning of next year. Pop Proof The pressure within the LEMV’s helium envelope is low enough that if it is somehow shot or punctured, the ship will neither explode nor tumble from the sky. Unmanned The military plans to deploy the LEMV without anyone on board. Autonomous sky trains, made up of a series of ships tied together, are a possibility (although current flight regulations require a pilot to steer ships through commercial airspace). Efficient The ship’s four diesel engines cost $15,000 to fuel on a three-week mission—one tenth the consumption of a helicopter and one quarter that of an airplane used on similar missions. [Image courtesy Northrop Grumman]

Heavy Lifter

Hybrid Air Vehicles, which teamed with Northrop on its design for the LEMV, is working on a set of three larger-capacity hybrid airships that can carry up to 200 tons and will be the biggest airborne carriers in the world, the smallest of which is larger than a 747. The HAV 606, is 607 feet long and has a helium envelope of 16 million cubic feet, twice the size of the Hindenburg. Hybrid Air plans to sell the ships, which take 24 months to build, for mining and oil exploration. Well-Balanced When fully loaded, the HAV is no longer lighter than air (the weight of the load is greater than helium’s lift) and its airfoil design, wide and aerodynamic, becomes crucial for staying aloft. Dock Anywhere Landing skirts, which allow the craft to touch down, are retractable and amphibious, so the LEMV can land on ground or water. The crew activates a vacuum anchor when the craft lands, which does away with the need for a mooring tower. Roomy Interior A payload container can carry the weight of up to 85 humvees. [Image via BBC]

Fish Out of Water

Unveiled in 2009 by the EMPA, the Swiss federal laboratories for materials science and technology, this balloon has electric actuators attached on either side of its body. When voltage is applied, polymers in this 26-foot-long helium-filled balloon’s skin expand and constrict like a fish, propelling the craft silently. Christa Jordi, the lead scientist on the project, says the trout balloon could be used in such sound-sensitive situations as spy missions, animal observation and stadium events. The Flaming Lips need one. . . . Shock Propulsion Dielectric elastomer actuators act as artificial muscles, compressing and expanding when charged with electricity. Bone Structure A thin and rigid carbon-fiber-reinforced epoxy skeleton runs lengthwise through the “fish” and, like a spine, bends without any hinged joints. Clear Skin The helium-tight membrane is made of Heptax, a plastic that’s also used to seal food products [Image courtesy EMPA]