The U2 was subsonic. Also, un-powered gliders can get up to impressive altitudes.
https://www.airbus.com/newsroom/press-releases/en/2018/09/ai...
https://www.airbus.com/newsroom/press-releases/en/2018/09/ai...
I’m confused by the article and the above comment. Isn’t a glider by definition unpowered?