This is the multi-billion dollar program behind the US military's runaway blimp

A US military blimp, part of a multi-billion dollar surveillance program, has broken free of its tether in Maryland and was floating across the northeastern United States.

The rogue blimp is one of two airships that is part of the JLENS program - Joint Land Attack Cruise Missile Defense Elevated Netted Sensor Systems - built and designed by Raytheon.

The blimp, before breaking loose, was tethered alongside the other JLENS blimp in the Aberdeen Proving Ground in Maryland. The blimps were intended to be responsible for defending against possible cruise-missile attacks and other potential threats to Washington, DC, and other East Coast cities through the use of high-detailed radar imaging.

The two JLENS blimps were designed to operate in concert. One of them provides constant 360-degree scanning, covering a circular area from North Carolina to central Ohio to upstate New York, even as the blimp remains stationary over suburban Baltimore. The other focuses on more specific targets. Together, the blimps track missiles, aircraft, and drones in a 340-mile radius.

Both blimps were designed to be unarmed and unmanned. But the surveillance they provide would be relayed to air, ground, and ship-based weapons which would be used to intercept an incoming cruise missile.

According to Defense News, the JLENS blimps are designed to stay in the air for 30-day stretches at a time while reaching a tethered altitude of 10,000 feet. From that height, the blimps were intended to provide surveillance across air, land, and sea.

Raytheon notes that the blimp floats by helium-filled aerostats - and that the program's radars were intended to "protect a territory roughly the size of Texas from airborne threats."

As of the end of 2014, the JLENS project cost the government $2.8 billion. Congress has approved another $43.3 million for the first year of the JLENS operational test.

Ultimately, despite the massive cost of the program, the JLENS was intended to save the government money.

"The analysis we've done says it's about five to seven times less than operating a fleet of aircraft to cover the same area over the same time period," Douglas Burgess, Raytheon's JLENS program director, told the Air Force Times in 2014.

Despite the supposed benefits of JLENS, the program had been plagued with roadblocks even before one of the blimps managed to escape. According to an investigation by The Los Angeles Times, the blimps have faced such issues as being unable to distinguish friendly and threatening aircraft, being grounded by bad weather, and being incapable of providing continuous surveillance for 30-day periods.