This is a U.S.-built V-2 rocket engine made by the North American Aviation Company in 1947-1948 as part of their Navaho missile project. When North American started the project, it had no experience with rocket engines and built six V-2 engines to learn as much as possible about the construction of large-scale rocket engines. However, the engines were not fired in tests.
As Navaho expanded, North American developed a radically new and improved liquid propellant engine that was the start of the evolution of large-scale engines in the U.S. They included engines for the Redstone, Jupiter, Thor, and Atlas missiles and for the Saturn V Apollo launch vehicle and Space Shuttle. The U.S.-built V-2 engine was donated to the Smithsonian in 1970 by Rocketdyne.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.