Shown here is the X217C1 experimental Jet-Assisted-Take-Off (JATO)) rocket motor, made in September 1957 by the Alleghany Ballisrtics Laboratory and powered by a double-base type propellant. The Navy's bureau of ordnance acquired this motor, perhaps for a larger missile system.
Donated by the U.S. Army (Fort Benjamin Harrison).
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.