There is a nice summary on the XB-19 in Wagner's 'American Combat Planes'. From what I understand the XB-19 was never destined to be produced in numbers, it was more of a "flying laboratory" than a weapon. It was all part of the Air Corps 'Project D', a long-range bomber idea
"investigating the maximum feasible distance into the future".
This design's main purpose was to investigate how far a bomber could fly, and of course this meant a 'large' aircraft.
Contracts were offered to Douglas and Sikorsky but in the end Sikorsky's contract was cancelled with a payout of $103,000.
Douglas knew and told the Air Corps that by the time the XB-19 flew it would be obsolete. The Air Corps understood but told them to press on. Douglas attempted to rid itself of the project in August 1938, arguing that it was becoming expensive ($4 million for Douglas), obviously obsolete, with increasing weight and wasting personnel better utilised on profitable contracts. The Air Corps 'insisted' that Douglas proceed with the $1,400,000 contract.
After seven years of engineering challenges, it finally flew on the afternoon of June 27 1941.
Sikorsky's unsuccessful design, the XBLR-3. Intended wingspan of 205ft with an all-up weight of 120,000lbs.
1/25th wind tunnel model at Langley Research Centre of NACA 1936...