For the first time, one of the Pentagon's spy blimps successfully detected and tracked an anti-ship cruise missile, which the Navy then proceeded to blast out of the sky. But it's only a marginal success for the once-hyped blimp program. Once sweeping in scale and designed to use radars to help shoot down enemy missiles – a threat we could potentially face during a war with Iran – the blimps have seen drastic cuts after nearly $2 billion in development costs and years of delays.

The Raytheon-designed spy blimps, called the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor or JLENS, used its radars to home in on a test cruise missile during a demonstration Friday at White Sands Missile Range in New Mexico. After the blimps detected the test missile, the Navy fired a Standard Missile-6 interceptor and shot the incoming missile down. "It was a very successful intercept, and I'm pleased to say lots of pieces of the target scattered over the desert," Mark Rose, Raytheon's program director, told reporters during a teleconference Monday.

And on paper, the blimps sound better than in practice. Seventy-five meters long and almost as wide as a football field, a JLENS is actually not one – but two – blimps touted as a missile-defense radar in the sky. The Pentagon has hoped for years to field the blimps – designed to float at 10,000 feet for up to a month at a time – as a tool for tracking missiles, planes and boats.

In the event of a war with Iran, the blimps are designed to float calmly above the Persian Gulf, while defending against incoming missiles that could sink ships. The blimps' sensor range – about 342 miles – reaches farther than the Air Force's E-3 Sentry early-warning plane, while staying on guard for longer and using less fuel and manpower. The sensor range also reaches far enough that it could cover a sizable chunk of the Gulf including the strategic Strait of Hormuz waterway.

But the JLENS also has an inglorious history. First proposed in 1998, the Pentagon had by 2007 planned to build 28 blimps – divided into 14 pairs of two when deployed – at a total cost of $1.4 billion. By 2012, the military had already spent $1.9 billion, more than the original cost, and didn't have a single blimp ready to go. The program also needed another sum of $6 billion to field all the blimps by the year 2014.

The program was also running into problems. A mobile mooring station, which anchored the blimps, was delayed; it needed more armor than originally envisioned. The software powering the radars was also incompatible with a similar Army air defense system, which forced another delay so the military could standardize the two networks. In the fall of 2010, a prototype was destroyed when a commercial airship crashed into it after becoming unmoored during inclement weather. That further added to costs as the Army built a replacement.

This year, the Pentagon all but killed it. The 14 pairs of blimps turned into two, which is expected to save $2 billion in costs. A March report from the Government Accountability Office noted the JLENS now has a "stable design" (.pdf) after fixing bugs with the software, but noted that design changes still pose a risk that the whole project could be canceled.

But the two survivors, including the one tested last week, are still slated to be completed. The blimp's developer has also pushed hard to sell it. The blimps are "significantly less expensive to operate than a fixed-wing surveillance aircraft because it takes less than half the manpower to operate and has a negligible maintenance and fuel cost," Raytheon vice president David Gulla said in September.

Which is correct. But the cost isn't so negligible given the billions spent, and the billions more required to field them in any substantial number. It's still a wonder how they've managed to survive for this long.