09/30/2010. Remarks by Johan Visschedijk: "The XB-38 was originally a B-17E, s/n 41-2041, which had been turned over to Vega for study during the formation of the Boeing-Vega-Douglas manufacturing pool. At Army Air Corps request, Vega initiated a study to improve the basic bomber by changing from 1,000 hp air-cooled Wright R-1820-97 nine-cylinder air-cooled radial engines to 1,425 hp Allison V-1710-89 twelve-cylinder liquid-cooled V-engines.
Negotiations for development of the new design, known as Vega V-134-1, began on March 4, 1942, and a contract was signed on July 10. The basic airframe was unchanged except for necessary revisions to accommodate the new engines. The oil coolers of the B-17E were in the leading edges of the wings but were moved to positions under the propellers on the XB-38, and the coolant radiators for the Allison engines were mounted in the leading edge of the wing between each pair of nacelles.
First flown on May 19, 1943, the XB-38 showed a slight improvement over the standard B-17E, however, full comparison with the radial-engined B-17 series could not be made because the XB-38 was lost on June 16 as a result of an engine fire that could not be extinguished. Due to the marginal performance improvement and the demand of in-line engines for the P-38 and P-40 fighters, work on an additional XB-38, s/n 42-73515 was cancelled."