X-1, NASA history collection. NASA public domain image colelction.

E49-007A roll-out of the Boeing B-29 Superfortress, bomber with the Bell Aircraft Corporation X-1-2 mated and ready for flight. NACA Flight 33 was flown on September 23, 1949, as a pilot familiarization flight with NACA pilot, John H. Griffith at the controls. Griffith reached a top speed of Mach 0.998 during the flight. Sep 1949 NASA Photo / NASA photo B-29 Project Description
NASA Identifier: 340414main_E49-007