Flyaway blimp? Funny. $2.7 billion? Less funny.

Many laughs were had last month when an Army blimp broke free of its tethers and went on a joyride over Maryland and Pennsylvania – with everyone from Sen. John McCain to national security leaker Edward Snowden getting in on the joke.

But that wild goose chase may end up being very serious, and expensive, for Raytheon, which gets most of the $2.7 billion taxpayers are spending on a threat-detection system that the Pentagon itself admits has “low system reliability.”

The Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System, a mouthful we'll just call Jlens, is a radar array kept aloft at 10,000 feet by pairs of 242-foot helium aerostats and intended to identify threats to the Eastern Seaboard. In theory, Jlens would detect enemy planes, missiles and drones over a radius of 340 miles and forward the information to U.S. fighter jets or missile systems, which would then go in for the kill.

That is the theory. The reality has been much different. Initiated in 1998 with a $292 million contract, the project got an understandable boost after the attacks of Sept. 11, 2001; in 2005 the military signed on for 27 of the craft. But since then, the project has been a series of expensive follies.

While there were the usual mishaps in early development, software glitches and the like, a bigger setback came in 2010, when a civilian balloon crashed into a Jlens blimp and sent it crashing to the ground. There went $182 million.

According to a stellar piece of investigative reporting by David Willman of the Los Angeles Times, a 2012 Pentagon report noted that the system struggled to stay aloft and had trouble telling friend from foe. An assessment the following year concluded that Jlens “did not demonstrate the ability to survive in its intended operational environment.”

A large contingent of Army brass, concerned also that the whole system required too much ground support to give it effective mobility, has spent years trying to end the program. True to form, a few members of Congress whose states benefit from the program – and who are lobbied by notables like retired Gen. James Cartwright, a former vice chairman of the Joint Chiefs of Staff – have kept it alive. But maybe not much longer.

An Army combat readiness team from Fort Rucker in Alabama has already begun an investigation of the runaway blimp – after authorities were able to deflate it, that is. The Pentagon has now put the entire Jlens program on suspension. The Republican and Democratic top members of the House Oversight Committee told the Pentagon that “this event raises serious questions about the value and reliability of Jlens.”

Rep. Jackie Speier, a Democrat on the House Armed Services Committee, called it “an egregious example of the corrupting nature of the revolving door for military generals who then go on to serve on defense contractor boards.”

I wish the representatives good luck in killing Jlens – and they seem to have McCain on their side – but it has been one of those Pentagon acquisitions that time and time again escape death by budget cut.

Other recent “zombie programs” have included an alternative engine design for the F-35 Joint Strike Fighter that nobody wanted and ended up costing $450 million, and the infamous Expeditionary Fighting Vehicle, which the Pentagon tried to remove from its budget three times before it was finally put to death in 2011, with up to $3 billion spent.

Unfortunately, the Jlens fiasco wasn’t the only recent crash involving an inflatable. On Oct. 11 in Kabul, Afghanistan, a British military helicopter hit the tether of a surveillance blimp moored at NATO headquarters and crashed, killing five.

The military use of inflatables dates to the Battle of Fleurus in 1794, when Napoleon’s army used one to spy on enemy positions. Sometimes these initiatives have been great successes, as with the U.S. Navy airships that protected World War II convoys from German U-boats. But many others have ended in wasted money and lives.

Jlens stands out among that crowd only in terms of total expenditure; let’s just be relieved that this time, nobody ended up getting killed.

Tobin Harshaw writes editorials on national security, military affairs and education for Bloomberg View.