This period also saw the introduction of non-flammable helium as a lifting gas by the United States, while the more dangerous hydrogen continued to be used since the United States had the only sources of the gas at that time, and would not export it.
This era witnessed the introduction of non-flammable helium as a lifting gas by the United States, while the more hazardous hydrogen continued to be utilized due to the U.S.'s exclusive possession of the gas supply and its refusal to export it.