So no matter what chain of events led up to the explosion, it was helium's scarcity that killed the airship. And today, the same gas—rare as ever—is putting a major cramp in deep sea diving operations.

The US Navy's divers are responsible for a wide variety of salvage and rescue tasks, from prying sunken wrecks off the sea floor to bringing distressed submarines to the surface. But every one of those divers needs oxygen that's cut with expensive helium (rather than nitrogen, which makes up most of the atmospheric cocktail we breathe on the surface). So to reduce costs—an enable more missions—the Navy has developed a new diving apparatus that rescues the helium from a diver's exhalations.

For shallow diving, a mixture of oxygen and nitrogen is fine. But nitrogen is bad for deep divers, because it's impractical for them to ascend slowly enough to prevent the gas from causing the bends and other agonizing physiological conditions. So for deep operations, divers get pumped a mixture of oxygen and helium from the surface. "But metabolically, the diver's only used about 5 percent of the helium gas in each breath," says John Camperman, the senior diving and life support scientist at the Naval Experimental Diving Unit in Panama Beach, Fl. A lot of oxygen gets wasted this way, too, bubbling away to the surface with every exhale.