This book presents a little-known aspect of America’s aircraft development during the Second World War in emphasising unique and non-production aircraft or modifications for the purpose of research and experimentation in support of development, advancing technology or meeting narrow combat needs. It describes important areas of aviation weapons maturation during war with an emphasis on advanced technology and experimental aircraft configurations. The great value of the work is of little known or minimally documented projects, which significantly advanced the science of aeronautics, propulsion, aircraft systems and ordnance, but did not go into production. Each chapter introduces another topic by examining the state-of-the-art at the beginning of the war, advantages pursued, and results achieved during the conflict as well as examining the secret modifications or experiments that are little known. Illustrated throughout, this is an important single source for a fascinating and diverse collection of wartime efforts never-before brought together under a single cover.