File:Boeing NB-52A carrying X-15.jpg

Summary
Boeing NB-52A (s/n 52-003) permanent test variant, carrying North American Aviation's legendary X-15, and mission markings. Horizontal X-15 silhouettes indicating glide flights, near-vertical ones recording powered ones.

https://commons.wikimedia.org/wiki/File:Boeing_NB-52A_carrying_X-15.jpg