The X-planes conjure up images of Chuck Yeager first breaking the sound barrier in the X-1 or the bullet-shaped X-15 streaking through the skies at over Mach 6. But there have been 48 more X-designations assigned, as well as many other experimental aircraft that did not fall into the formal X-series. This book is not limited to the formal X-series but also covers other experimental aircraft used by U.S. military & NASA. An outstanding collection of photos.