A few years ago, Russia wanted its designers to solve a torpedo problem. Due to the resistance of the water, torpedoes could not go very fast compared to bullets, missiles and other overground weapons. Could they be sped up, maybe with some kind of rocket engine?
One brilliant fellow had a great idea. Rockets always blow out the back to push a missile forward. What if we blow out the front instead?
Now I can hear all you folks in the back row laughing. Help your colleagues pick themselves up off the floor now, and listen closely.
Obviously blowing all the hot gases out the nose would not work. But what happens if we direct some of them that way? What if we make some small vents like in a shower head, and spray out hot gases, while the engine pushes the torpedo forward? It turns out that this turns the water in front of the missile to foam, reducing resistance, and allowing a very big boost in speed as the missile is now travelling through foam.
It is thought that the Bermuda Triangle is caused by a similar thing, when methane clathrates under the bottom of the ocean suddenly reach melting temperature and become gas, causing billions of little bubbles to rise up explosively, taking sand and rock with it, and turning a column of ocean water into foam. Any ship which is there, or which approaches too closely, slips down into the foam column and rapidly plunges to the bottom. As the clathrates are exhausted, the sand and rock cover it over again.
Anyway, the torpedo solution worked well. But in Russia, things do not just end when a new technique is successfully used to solve a problem. For Russian engineers, this is just the beginning.
Russian engineering schools teach a technique called TRIZ which involves exploring all the possibilities of a new technology or technique or a new physical principle. This is a major reason for the great leap forward of the Russian military which they put on show when they entered Syria.
Other designers wondered what would happen if you do this same thing to a missile, travelling in the air. It turns out, that you can also get a speed boost form this. Of course there are some other techniques being used as well because the air does not cavitate like a liquid, but it is possible to reduce the air resistance ahead of a missile nosecone and that's what these hypersonic vehicles do. US military pilots have actually filmed Russian hypersonic test vehicles and reported them as UFOs, meaning alien spacecraft. However since that time, new training has made it clear that UFO is a term for unknown origin objects and the information should not be released publicly since these are most likely foreign military or even domestic experimental craft. The thing is that when domestic experiments are done, the Pentagon can ensure that US military pilots do not operate in the area. Those hypersonic craft where the new Russian reentry vehicles under test.