Although hydrogen is twice as buoyant as helium, and would be more effective in lifting an airship off the ground, hydrogen gas is extremely dangerous. The German airship, or zeppelin, the Hindenburg, the world’s largest airship at the time, was destroyed on May 6, 1937, in Lakehurst, New Jersey, when it exploded into a huge fireball while attempting to land. Thirty-six people died in the explosion.

In 1937, the United States was about the only source of helium in the world, mostly from one gas well in Texas. The Nazis wanted to buy helium for their zeppelins, but the United States refused to sell it to them—as it was considered a strategic resource. Helium is formed from the radioactive decay of uranium and thorium in rocks. It is used today to cool devices and make them superconductive. As a result, the amount of helium available is rapidly decreasing.