the military was interested in helium for balloons and dirigibles. the us army built the first helium extraction plant in 1915 at petrolia, texas, where a large natural gas field averaged nearly 1 percent helium. the united states navy established three experimental helium plants during world war i, to recover enough helium to supply barrage balloons with the non-flammable, lighter-than-air gas. two of the experimental plants were north of fort worth, texas, and recovered helium from natural gas piped in from the petrolia oil field in clay county, texas.