By Phil Stewart and Yeganeh Torbati

WASHINGTON (Reuters) - A high-tech U.S. military blimp designed to detect a missile attack came loose on Wednesday and wreaked havoc as it floated from Maryland into Pennsylvania, dragging more than a mile of cable and knocking out power to thousands.

The U.S. military scrambled two armed F-16 fighter jets to keep watch as the massive blimp traveled into civilian airspace after coming untethered from its base at Aberdeen Proving Ground, a U.S. Army facility 40 miles northeast of Baltimore.

Pentagon officials said they were unsure why the 242-foot-long blimp broke free at 12:20 p.m.. Military officials wrestled for hours over the best way to safely bring it down, but eventually it deflated on its own.

The blimp, part of a $2.8 billion Army program, landed in Exchange, Pennsylvania, a community outside Bloomsburg, about 150 miles north of the Aberdeen Proving Ground.

John Thomas, a spokesman for Columbia County emergency management agency, said he had no details on the landing. "It's pretty rural out through there," he said, adding there were no reports of injuries.

The blimp's travels caused widespread damage, local officials said. At one point, 30,000 Pennsylvania residents were without power, the governor's office said.

"The tether attached to the aircraft caused widespread power outages across Pennsylvania," said a statement from Governor Tom Wolf's office.

The blimp's travels caused a sensation on social media, with hashtags like #Blimpflood and #Blimpmemes ranking among the most trending topics. At least two Twitter parody accounts sprung up, gaining nearly 2,000 followers in just under two hours.

The attention was unlikely to be welcomed by the Army, which calls the program the Joint Land-Attack Cruise Missile Elevated Netted Sensor System, or JLENS. The program was restructured after it overran cost estimates, the Government Accountability Office said in 2014.

The program is comprised of two blimps, each 242 feet long. The second blimp will be grounded until the military inspects it and finishes an investigation into the unmooring, said Navy Captain Scott Miller, a spokesman for the U.S. military's North American Aerospace Defense Command, or NORAD.

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The system itself is still in a testing phase. Manufacturer Raytheon Co's website says it would become part of the defenses that help protect the metropolitan Washington, D.C. area. (Link: http://rtn.co/1PUJnjY)

Raytheon's website says the blimps are meant to be tethered to the ground by a "11/8 inch thick super-strong cable," which should withstand 100 mile-per-hour winds. Electricity runs up the cable and powers the radar, the website says.

NORAD said the blimp became untethered while at an altitude of just 6,600 feet, far below its maximum recommended altitude of up to 10,000 feet.

By early afternoon, it had climbed to 16,000 feet as it traveled into Pennsylvania.

NORAD said the system was designed to defend against threats beyond cruise missiles, to include drone aircraft and "surface moving targets" such as swarming boats and tanks.

(Reporting by Phil Stewart and Yeganeh Torbati in Washington, Joe McDonald in Exchange, Pennsylvania, Eric Johnson in Seattle and Scott Disavino in New York; Editing by Bill Trott and David Gregorio)