The U.S. military has two giant, unmanned surveillance blimps it uses to watch the East Coast from a base in Maryland. And one of them escaped its tethers Wednesday and floated aimlessly over Pennsylvania, downing power lines and cutting off electricity for tens of thousands of residents.

The incident started shortly after noon, when the blimp became detached from its anchor, NORAD said. Two F-16 fighter jets were scrambled to ensure it didn’t collide with other aircraft. By late afternoon, the dirigible had come down to the ground near Moreland Township in Pennsylvania — after drifting more than 100 miles — but not before leaving a trail of damage in its wake.

It was unclear how the aerostat got loose and how it came down, said John Cornelio, a spokesman for NORAD. He added it was possible that the aerostat's helium could have run out.

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“We can assume that an aerostat like this will eventually come back to Earth,” he said.

The blimp wreaked plenty of havoc. Frederick Hunsinger, the public safety director for Columbia County, Pa., said in an interview that the blimp’s heavy tether dragged for 20 miles across his county. There were no injuries within county borders, but the damage caused 35,000 to lose electricity, he said. Bloomsburg University of Pennsylvania canceled classes as a result; 911 phone lines were overwhelmed.

“It was a lot of chaos, initially,” Hunsinger said. “It pulled down power lines and utility poles.”

Known as the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System, or JLENS, the blimp is technically an aerostat -- a term for a lighter-than-air craft that is tethered to the ground. The $2.7 billion program is on a three-year test run to see whether it can help detect cruise missiles or enemy aircraft from 10,000 feet above ground.

This type of craft has been used for surveillance by the U.S. military in Iraq and Afghanistan. And while a listing blimp bumbling across Pennsylvania was a spectacle to behold, the incident is renewing questions among privacy advocates and others over why such powerful battlefield technology, developed by private companies, was brought back to the homeland.

The JLENS program “continues to drain money from taxpayers even though it serves no strategic purpose,” Rep. Jackie Speier (D-Calif.) said. “This incident is just another example of the problems inherent in an ill-conceived network of floating blimps that don’t provide any advantage over aircraft we’ve already bought.”

She added that “it’s a good time to consider slashing this program for good.”

The aerostats were set aloft last year on Army-owned land about 45 miles northeast of Washington, near Aberdeen Proving Ground. From their vantage point, they could cast a vast radar net from Raleigh, N.C., to Boston and out to Lake Erie, with the goal of detecting cruise missiles or enemy aircraft so they could be intercepted before reaching the capital. The aerostats are capable of spotting airborne objects up to 340 miles away and vehicles on the ground or water up to 140 miles away.

[GRAPHIC: How does an aerostat work?]

The idea of a runaway surveillance blimp set social media afire. Even Edward Snowden, the former government contractor who revealed the extent of government spying, weighed in from his asylum in Russia:

Aerostats installed at bases in Afghanistan and Iraq were also equipped with powerful surveillance cameras to track the movements of suspected insurgents as well as U.S. soldiers. When Army Staff Sgt. Robert Bales murdered 16 civilians in Kandahar in March 2012, an aerostat captured video of him retreating from a base in the early-morning darkness with a rifle in his hand and a shawl over his shoulders.

The craft were built by defense contractor Raytheon. And in 2013, the company touted an exercise in which it outfitted the aerostats planned for deployment in suburban Baltimore with one of Raytheon’s most powerful high-altitude surveillance systems, capable of spotting individual people and vehicles from a distance of many miles.

But the Army has said that the purpose of the radars on the JLENS in Maryland is to protect the U.S. from missiles and attack jets — not to monitor individuals. In a statement to The Washington Post last year, the Army said that “the primary mission … is to track airborne objects. Its secondary mission is to track surface moving objects such as vehicles or boats. The capability to track surface objects does not extend to individual people.”

The helium-filled balloons are 74 meters long, or three-quarters the length of a football field. Raytheon says on its Web site that the chance of the tether breaking “is very small” because it is made of a strong fiber known as Vectran that the company says “has withstood storms in excess of 100 knots.”

The tethers do not just the blimps from floating away; they carry power to the radar and transmit data to a computer on the ground.

While a breakaway is “unlikely,” Raytheon said on its Web site, if one does get loose, “there are a number of procedures and systems in place, which are designed to bring the aerostat down in a safe manner.” A Raytheon spokesman declined to comment on the system Wednesday.

Like many highly technical defense programs, JLENS has suffered “cost increases and schedule delays due to setbacks in development,” according to the Government Accountability Office, which said that the total program cost was $2.7 billion.

After facing problems, defense officials conducted reviews of the program in an attempt to “verify that design risks have been minimized,” the GAO said.

Jay Stanley, a senior policy analyst with the American Civil Liberties Union, questioned whether JLENS has been worth the cost.

“In some ways, it’s a perfect metaphor for the surveillance state we have — hugely expensive and totally out of control,” he said. "And it seems that people in charge of mooring the thing could also do with some oversight."

John Pike, a defense analyst at globalsecurity.org, added that it’s no surprise that the program has run into problems. “All of these things are protracted and troubled,” he said. “All of them are capabilities in search of missions.”

But he said that the system “is a real solution to a real threat. … Everyone has drunk the Kool-Aid on missile defense.”

The Army says the aerostats being deployed near D.C., will not be equipped with cameras like the ones in Afghanistan. The Post's Craig Timberg, explains how aerostats work and how powerful their radar and camera sensors can be. (Kate M. Tobey and Gillian Brockell/The Washington Post)

Aerostats are also used by Israel to monitor the Gaza Strip and by the United States to eye movement along southern border areas. Even a rifle shot through an aerostat will not bring it down, because the pressure of the helium inside nearly matches the pressure of the air outside, preventing rapid deflation.

The aerostat in Pennsylvania may not have suffered a bullet shot, but its deflation became a scene nonetheless. Uriah Derstine, a 19-year-old sophomore at Bloomsburg University, said he left campus after classes were cancelled, but had trouble making his way to his home in Turbotville, Pa., because of the hubbub.

“It took me 45 minutes to travel about five miles because of stop lights being out -- they had to have crossing guards out directing traffic,” he said. On his way home, Derstine said he met up with his father and grandfather, who also live in the area and decided to see the blimp for themselves.

By the time they approached the aircraft, it was already down. “It just looked like a big piece of plastic draped over the trees,” Derstine said.

A high-tech military blimp came loose from its moorings and floated 16,000 feet over Maryland and Pennsylvania. Officials say the blimp has since descended near the ground. (Reuters)