The U.S. military has launched the second of two helium-filled airships near Baltimore to test an East Coast missile defense system.

The confirmed launch Wednesday at the Army's Aberdeen Proving Ground completes the aeronautical part of the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System, or JLENS.

The radar-equipped aerostats are tethered to concrete pads 4 miles apart. They're designed to float unmanned at 10,000 feet.

During the three-year test, one balloon will continuously scan 360 degrees from upstate New York to North Carolina's Outer Banks, and as far west as central Ohio. The other carries precision radar to help the military on the ground pinpoint targets.

The aerostats don't carry weapons. Enemy missiles would be destroyed by weapons launched from the air, the sea or the ground.