The Sänger Silbervogel (also known as RaBo which means Rocket Bomber) was a rocket-powered long range continental bomber design suggested for the Amerika Bomber project in the late 30s. Developed by aerospace engineer Eugen Sänger and physicist Irene Brant, it was truly one of the most unorthodox designs ever built by the Germans and now probably my favorite. Only a wind tunnel version was made.


AMERIKA BOMBER PROJECT
The principle of reaching the US without the use of a fleet was something the Germans were really concerned about. The US were extremely hard to touch due to one major advantage: location. The American continent is separated by the Pacific Ocean in an Asia context, but by the Atlantic for Europe. The distance between the States and Germany is ~5800 km due to that large sea, so only a fleet could reach it. However, a fleet proved to be easy pickings for torpedo bombers and medium bombers, and with the USN ships also kicking in, it would've been extremely tedious to actually continue a sustained bombing attack, since you'd need to set foot on American territory and have a constant supply line for the materials to arrive, which will take months. Knowing about the US's large budget, a bomb raid on the US proved to be extremely hard, with only the Japanese actually reaching US soil, but it was a loss while the US was attacked by surprise. With that in mind, in 1938, the Amerika Bomber project was formed, to make a trans-Atlantic bomber that could carry a big payload to Murican soil. However, designs started coming in only in the spring of 1942, and only two planes actually flew. However, the project was deemed too expensive and the Luftwaffe was already having a hard time in '42, so the concept got scraped completely.
Now to get to the actual plane. In order to reach the US, the Silbervogel was meant to travel at 145 km altitude max and stratospheric altitude at minimum (~50 km), which is a lot higher than even most modern day jets and reach an estimated max speed of Mach 18. In order to do just that, there was an entire process. Let me show you:
STEP 1: TAKEOFF
The Silbervogel was meant to takeoff from a 3 km rail, being on a rocket-powered sled delivering 600 tons of thrust for 11 seconds, making it reach a speed of Mach 1.5 after a 30 degree climb to 1.5 km. Here is a representation of how the sled would look like:

After reaching 1.5 km, the Silbervogel would fire its main engine for 8 mins, delivering 100 tons of thrust, making it go to a shocking speed of Mach 18 until it reaches 145 km altitude, though some claim it could reach 280 km altitude. The engine burns 90 tons of fuel during the process. To WWII standards, this is not just obscene, it's like you might as well bring the USS Entreprise to our time. The V-2 feels like it's underground compared to it. Anyway, time to go to my favorite part:
STEP 2: TO AMERICA!
The Silbervogel had the strangest flight pattern I have ever seen. I dare you to find something weirder. What you're probably wondering is how it could get to America without any fuel. Well, it's quite simple my friends, IT SKIPS TO AMERICA. Yes, it SKIPS. No worries, I'll explain the hilarious process.
Basically, when its 8 min run is complete, gravity starts pulling it in, which is normal since the thing weighs almost 10 tons on empty, and would weigh nearly 103-110 tons fully loaded. Anyway, it descends to the stratosphere, and on contact with the much denser air, it springs back up. Hell, I have a diagram to show you:

Now, this technique also has the benefit of cooling the heat from the friction, therefore not making the deadly cargo explode. The skips start lowering in intensity according to the pic due to the effects of drag against the stratosphere. Eventually the Silbervogel would reach Murca, the land of many freedums and stuff, then drop a 3629 kg bomb. Disappointing, I know, but if the Germans had the nuke before the US did and had the Silbervogel, everyone would think it's a work of God, thus causing a MASSIVE psychological effect on the US and the Allies, since the Germans would apparently blow up and irradiate cities on cue. In fact, that would already be the case with the crappy bomb it has. Anyway, it's time for the Silver Bird to go back to its nest so its pilot can have a nice cup of coffee for a job well done.
STEP 3: LANDING
The Silbervogel's skips are calculated with exact precision in order to land right back in Germany. The pilot would slow down probably by the use of really powerful airbrakes, and land with tricycle gear. The job is done without the loss of a plane nor without any single soul aside from Ze Germans knowing what just happened.
STEP 4: COFFEE BREAK
*somewhere in a Luftwaffe air base's mess hall*
High ranking officer: How was job? Was good?
Silbervogel pilot: Ja, was good. Best time of life. When do that again?
END
Now, the Luftwaffe knew how valuable this info was. It was so inhumanely effective in theory. However, the extremely poor bombload meant that actually hurting America hard was hard, especially since the precision of the attack was as large as the US itself obviously. And here you thought B-17s were inaccurate... The other problem was how extremely complicated it was to make such a monster, thus not being good for even limited production. Another problem was that there was a screw-up in Sänger's calculations, which showed that the aircraft's temperature far exceeded the results he had predicted. Of course, a better heat shield would've solved that, but it would compromise the already crappy bombload even more.
HOWEVER, that DID NOT mean that it was a crappy design never to be seen again like the Komet. In fact, let me show you that it had a HUGE impact on the world, yet was so unknown.
GLOBAL INFLUENCE:
Like I said, the Luftwaffe absolutely loved the concept. It would've been effective and even more shocking than V-2 attacks. However, the Soviets also thought that when they saw the blueprint. Due to how incredible it was, Joseph Stalin ordered his son, Vasily and scientist Grigori Tokaty to kidnap Sänger, so that they can force him to spill the beans about the entire glide sub-orbital strike bomber concept of his to the benefit of the USSR, but the attempt failed. Nevertheless the Soviets tried copying the design. The Keldysh was born.

However, its speed is ridiculously low compared to the Silver Bird, and it depended on the rocket to fly unlike its German counterpart, which was an orbital glider. This did inspire the Soviets to make new concepts of intercontinental nuclear cruise missiles though.
But this isn't the best part. The Americans also got hold of the Silbervogel project, and they were interested. With the glide bomber in mind, in 1957, Boeing created a orbital skipper of its own: the X-20.

Its performance was VERY similar to the Vogel's but it looked far less like a rocket. This was made possible thanks to German scientist Walter Dornberger, who had a detailed knowledge of the Silbervogel. While it did land a contract unlike the German original, it was still scraped later on. However, not all efforts went in vain. The entire concept that the Germans started led to the necessary knowledge to create a reusable spacecraft in which crew members can live in comfortably unlike the crowded space capsules. Yes, I am talking about the NASA Space Shuttle itself:

Who knew that the Germans' attempt at punching America in the face without needing to properly settle on US soil led to one of the main wonders of space? With the rocket tests of the X-15 and the glide tests of the X-20 coming from the Silber, the Space Shuttle was born and moving around the Earth's atmosphere never had been easier. Still being used today ain't it? Yes. Who to thank? The Germans during the Nazi regime surprisingly.
CONCLUSION:
The Silbervogel is a mad atmosphere skipping machine that would've made the US absolutely left clueless as to how a bomb magically started falling out of the sky, and Nazis indirectly made the first Space Shuttle concept.