Before the P-51 Mustang, the USAAF planned to use heavily-armed converted Flying Fortresses and Liberators to escort the Eighth Air Force's formations over Germany. This is the first history of their development, role, and failure, by an expert USAAF historian.

The XB-40 and XB-41 were secret, little-known experimental modifications of the B-17F and B-24D, respectively, into heavily-armed bomber gunships variously referred to as “convoy protector airplanes,” “bomber escorters,” or ”destroyer escort planes.” These aircraft were developed during the early war in response to the lack of a USAAF long-range fighter aircraft able to escort and protect beleaguered regular B-17 formations from the UK round trip deep into Germany. Unfortunately, these “protecters” were found to be unable to protect large formations as expected. During their construction each encountered numerous delays in the development and delivery of their various armament additions and improvements, particularly the Bendix chin turret. Being modifications of the bomber, they were to protect; after the addition of guns and ammunition they became overweight and also markedly tail-heavy causing center of gravity problems. The result of these alterations were protectors that did not have the performance of the bombers they were to protect. After releasing their bombs, a standard B-17F formation returning from a mission easily outpaced their overloaded escort protectors that carried no bombs. The YB-40 participated in only 14 lackluster operational service test missions during mid-1943 before being withdrawn from service. The XB-41 Liberator was a one-of-a-kind bomber escort which had similar problems as the XB-40 but never saw operational testing before also being cancelled for its poor comparative performance to standard bombers.

Over the past 75 years both the XB-40 and XB-41 have been chronicled in only a few rehashed magazine and online articles. Using many formerly classified documents from his large microfilm collection, in this book William Wolf presents their previously unpublished history. It describes in depth for the first time the politics and development and associated problems of both escorter types. The armament of each is described and depicted in detail, and the YB-40's operational service test missions are recounted from 92BG/327BG records. The history of these two escorters is described in the context of the USAAF's strategic bombing and concurrent fighter escort developments and undertakings during the European air war.