In the 1930s, the Graf Zeppelin made its first airmail delivery to the Americas. It was a spectacular sight, somewhat akin to aliens landing on earth. The German airship company was proud of the world's largest zeppelin, but were confronted from the beginning with what would eventually be the downfall of all such airships: how to make them profitable?
Instead, the Graf’s parent company, German Zeppelin Airship Works, decided to recoup costs by commissioning special stamps from the countries on the tour route. Only letters with these stamps on them would be accepted onto the airship, which would then deliver them to their destinations. This was the only commercial transatlantic air mail option available at the time, and was days faster than sending a letter by boat. Brazil, Bolivia, Germany, and Spain all made the Zeppelin stamps, and 93 percent of the proceeds from each stamp was funneled back into German Zeppelin Airship Works.
After some debate, the U.S. Post Office decided to get in on the game as well, designing and printing a run of Graf Zeppelin stamps in a matter of weeks. They called this a gesture of goodwill toward Germany, and pledged to also contribute 93 percent of the revenue to the Airship Works. Secretly, though, they expected that an enthusiastic population of American collectors would snap up most of the stamps, keeping them out of circulation, and ensuring that the Post Office held onto most of the money.
Well, as we know from the short-lived era of zeppelins, the scheme didn't work out in the long run. Read the story of the zeppelin stamps at Atlas Obscura.