This is a rare model of the U.S. Navy's Gorgon 3C missile, also called KU3N-2, which was powered by two Reaction Motors, Inc. liquid-fuel rocket engines each producing 350 pounds of thrust. It dates to 1945-1946 and was perhaps the U.S.'s first missile with two motors that operated simultaneously. About May 1946, the missile was redesignated the KU3N-2.
Only a dozen Gorgon 3Cs were built. Of these, six were used by the National Advisory Committee for Aeronautics (NACA) for high speed research. Their velocity approached Mach 1. The remaining six were expended in stability and performance flight tests for the Navy. The missile shown here was very likely one of the NACA vehicles and perhaps the only one extant. It was transfered to the Smithsonian in 1965.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.