The D-558-2 is mounted to a P2B-1 Mothership.
In this historical photo from the U.S. space agency, the Douglas D-558-2 #2 is being mounted under the left wing of the P2B-1 launch aircraft in 1956. The P2B-1 has been lifted on mechanical jacks in the hangar for a possible fit check or a rare attachment of the Skyrocket for a flight.
The National Advisory Committee on Aeronautics (NACA) was a precursor to NASA. NACA was created by Congress in 1915.
Each weekday, SPACE.com looks back at the history of spaceflight through photos (archive).