This book is about USAAF experiments to modify existing bombers (standard B17E and B24D), into heavily armed and armored gunships to accompany bomber formations at a time when fighter escorts could not make the full journey into Germany. It describes the conceptual planning behind the designs, the modifications of the airplanes to create them, and their deployments in the ETO. The book also describes the service histories and fates of each of the YB-40s sent to England. Only 13 were deployed and They performed 48 sorties. There is much discussion on the armaments of the designs. For the time, the turrets and hydraulic power control systems were quite sophisticated. There is also much discussion on the reasons for the failures of the bomber escort concept: excessive weight, poor manoeuvrability, poor rate of climb, armament not significantly greater than a standard B-17F. The book concludes with brief and interesting summaries of other experimental bomber escorts, including the escort version of the B-26, and the YB-29 escorter. Readers should find plenty of fascinating new information within this slim volume.