H2 (hydrogen, technically H2 but suffix slow to type!), was for a time used for efficient long-distance transport. The flying machines were ‘dirigibles' - a big word for big balloons. They were massive and able to transport tons of cargo and passengers over vast distances, albeit slowly due to their bulk, powered by petrol aero engines.
Hailed as a major triumph, there was a snag. H2 is flammable. The infamous Hindenburg disaster was just one of the fires that caused H2 to fade from the picture. It was soon replaced by helium, the next lightest gas (H2 has mass of 1, helium 4). The advent of more powerful petrol-powered aircraft made the balloons obsolete.
H2 rises! This is opposite to all our other fuels – petrol, diesel, kero, methane, LPG,…