Going as far back as the 1930s, when it was restricted because of its scarcity and use in naval airships. For example, the United States refused to sell helium to Nazi Germany -- which is why the airship Hindenburg was filled with hydrogen.
Going as far back as the 1930s, when it was restricted because of its scarcity and use in naval airships. For example, the United States refused to sell helium to Nazi Germany -- which is why the airship Hindenburg was filled with hydrogen.