The D-558-2 is launched from the Navy P2B-1S in this 1950s photograph. The early Douglas and NACA flights of the D-558-2s used only the airplane's jet engine and took off from the runway. This limited the aircraft's altitude and speed. The solution was to convert the D-558-2 to rocket or combined jet-and-rocket propulsion and to airdrop it from a B-29 converted to the Navy's P2B-1S configuration. The drop plane was P2B-1S serial number 84029. It had been built as a B-29A (Army Air Forces 45-21787) before being modified as a drop plane for the Navy. Dubbed ''Fertile Myrtle,'' the mothership used the call sign ''NACA 137.''