	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.