The past decade has seen an unlikely revival of a long-grounded technology. Military airships, last operational with the U.S. Navy in the 1960s, took back to the skies, propelled by soaring demand for long-endurance, low-cost aerial surveillance in Iraq and Afghanistan. Per flight hour, an airship costs a fraction of what a helicopter or a fixed-wing plane costs. But three of the most prominent new-breed airship programs came crashingback to earth in early 2012. A massive, in-development Air Force spy blimp, a Navy test blimp and an Army tethered airship that's part of an evolving missile-defense network -- all were canceled or curtailed. It might have seemed that the promise of a new generation of military blimps was, well, so much hot air. Military Airships: Hot Air or Soaring Promise?