| YB-40 Flying Fortress | |
|---|---|
 The prototype XB-40 was a Boeing B-17F modified by Lockheed Vega (Project V-139) by converting the second production B-17F-1-BO (s/n 41-24341). | |
| General information | |
| Type | Bomber escort |
| Built by | Lockheed-Vega |
| Primary user | United States Army Air Forces |
| Number built | 25 |
| History | |
| Introduction date | 29 May 1943 |
| First flight | 10 November 1942 |
| Retired | October 1943 |
| Developed from | Boeing B-17 Flying Fortress |
The Boeing YB-40 Flying Fortress was a modification for operational testing purposes of the B-17 Flying Fortress bomber aircraft, converted to act as a heavily armed gunship to support other bombers during World War II. At the time of its development, long-range fighter aircraft such as the North American P-51 Mustang were just entering quantity production, and thus were not yet available to accompany bombers all the way from England to Germany and back.