This is the S-3D liquid fuel rocket engine that powered the Jupiter, the US.'s first U.S. intermediate-range ballistic missile (IRBM) of 1,600 miles. The S-3 was a modification of the Redstone engine. It produced 150,000 lbs of thrust and used liquid oxygen and JP-4, a type of kerosene.
Rocketdyne developed the engine from 1956. The Jupiter became operational in 1960. It was used until 1963 and a modified version with additional upper stages, called the Juno II, was developed to launch spacecraft. Junos successfully launched the Explorer 7, 8, and 11 satellites. This object was donated to the Smithsonian in 1991 by the U.S. Army Center of Military History.