The Horten Plane is a new kind of airplane denominated Flying Wing. It appears in all Covert Front Series games. In the game it is called "Airplane of Unknown Construction" by the Intelligence Agency General Headquarters. It was designed by Karl von Toten. It was propably disigned by the Imagination Realizator. You can see it being developed in the Movie Reel 3.
It looks like a airplane in real life (watch there a Mateusz Skutnik's video about this relation). It is called Horten HO-229 and was made by Nazi German at the Second World War to bomb the United States in the project "Amerika Bomber".