The second F-1 Block Boeing built Fortress. First flew 30/5/42 before delivered to Cheyenne 11/6/42 The first XB-40 prototype was converted by the Vega division of Lockheed.as the Vega V-139. They converted a standard Boeing-built B-17F (serial number 41-24341) to escort configuration by adding a dorsal turret in the radio compartment position carrying a pair of 0.50-cal machine guns, a chin turret underneath the nose equipped with a pair of 0.50 cal machine guns, and twin gun mounts instead of the usual single gun mounts at each waist position. The regular top, belly, and tail turrets were retained, bringing total defensive armament to fourteen 0.50-inch machine guns. Additional protective armor was fitted for better crew protection. The bomb bays were replaced by storage areas which carried additional ammunition for the guns. The normal ammunition load was 11,135 rounds, which could be increased to 17,265 rounds if the fuel load was reduced. The first flight took place on November 10, 1942.; Tulsa 26/11/42; Mat Com HQ Wright Field as XB-40 armament test bed with a dorsal turret and pair of .50 cal machine guns in radio compartment to make a total of 14 guns aboard 15/9/43; 3704 BU Keesler 22/11/43; Recl Comp 4/4/45.