When WWII ended, American engineers examined a trove of Nazi concepts for rocket-powered weapons and aeroplanes. One of the most terrifying was Eugen Sänger's antipodal bomber, a manned supersonic plane designed to reach any city on Earth in one hour. Thank heavens it never worked.
Historian Amy Shira Teitel, who runs the fantastic Vintage Space blog over at Popular Science, brings us the story of Eugen Sänger, an Austrian rocket engineer who devised a concept for a rocket plane with a flat-bottomed fuselage. With the right propulsion—in this case, a rocket-powered slingshot on the runway—Sänger theorised that the plane would climb to the upper reaches of the sky, then skip across the lower levels of the atmosphere like a rock on a pond. He figured a pilot could reach any point on the globe within one hour, drop a bomb, and return to a predetermined landing site.
Thankfully, the concept was never built. Though Sänger first envisioned use as a passenger or cargo plane, he approached the Austrian government for funding in the mid-1930s by highlighting the antipodal plane's potential as an intercontinental bomber. Unfortunately for Sänger, but fortunately for history, the liquid propulsion system the concept was built around was too unreliable for use, and his project went unfunded.
Sänger continued to design experimental rockets for the Nazis, but his work was overshadowed by another Nazi rocket scientist: Wernher von Braun. The latter being German-born, he looked down on the Austrian Sänger's work, and von Braun convinced the Nazi government to quit funding Sänger's work.
Over at Vintage Space, you can read about how Sänger's skip-glide concept was tried by US engineers, while Joseph Stalin attempted to kidnap Sänger to work for the USSR. None of it worked out, and to this day the antipodal bomber remains a terrifyingly futuristic concept that never got off the ground. [Amy Shira Teitel; Vintage Space]