During the mid 1930s, the Army Air Corps wanted to push the technological envelope when it came to building a very long range bomber. Code named 'Project D,' this top-secret initiative would lead to the largest American bomber concept flown during World War II, the massive yet elegant Douglas XB-19.

Under Project D, two major manufacturers, Douglas and Sikorsky, were competing at a chance to build what would be the most advanced bomber ever conceived by the US. Much like modern classified bomber competitions, both manufacturers were given a designation, those being the XBLR-2 for Douglas, and XBLR-3 for Sikorsky, with BLR standing for 'bomber, long-range.' The Army ordered full-scale mock-ups of each design for evaluation.

In mid 1936, after reviewing both companies' mock-ups and design proposals, the Army Air Corps chose Douglas's XBLR-2 design for further development as it was thought to have been superior both in potential performance and its packaging of new technologies.

The XBLR-2 was truly an innovative design. The aircraft was an all metal, glass nosed, low winged, teardrop shaped behemoth that sat atop an unconventional (for the time period) retractable tricycle undercarriage. The tires on the XBLR-2's main landing gear were absolutely massive, dwarfing anything previously put on an aircraft.

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Originally, she was supposed to be powered by four 1,600hp XV-3420-1 twenty four cylinder, liquid-cooled engines. These experimental engines were basically a pair of twelve cylinder Allison inline 'v' engines mated together. Due to their complexity, and in and effort to cut costs while reducing an already languishing development schedule, the XV-3420-1s were replaced with 2,000hp Wright R-3350 air-cooled radial engines. Even though this change was made, the aircraft was built with complex and very powerful engines in mind as passages in the lower part of the aircraft's thick internal wing structure were designed for mechanics to service the engines in flight.

By 1938, the XBLR-2's research and development contract changed to a production contract, and the aircraft was re-designated the B-19. A single prototype was ordered, which would be named the XB-19 to designate its experimental nature.

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As the year wore on, funding for the massive aircraft was not consistent and progress on its construction was slow. Meanwhile, the aircraft's weight was ballooning. By late 1938, some three years after the original 'Project D' kicked off, even the Douglas project team was losing hope in their massive experiment and could tell that the big secret bombing was not a high enough priority for Army Air Corps. The XBLR-2 was in danger of being obsolete before it even left the ground. As a result, Douglas themselves requested the cancellation of the project. The Army refused, and construction continued somewhat sporadically.

By 1940, the Army declassified the giant bomber as many of its technologies were no longer cutting edge enough to justify keeping it secret. The press ran with the story and a large buzz was created about the Army's secret super-bomber that could fly across oceans and attack foreign countries while still having enough gas to make it home.

The XB-19 was finally finished in May of 1941. She was rolled out to the public sporting a massive 212 foot wingspan, just larger than that of a 747. The XB-19 was 132 feet long, and weighted 130,000lbs empty, which made it the largest aircraft America had ever built at the time. The aircraft could hold over 11,000 gallons of gas.

She was designed to be operated by a crew of 16, but an additional eight crew, which would consist of relief pilots and mechanics, could be carried for extended missions. Bunks and a complete galley were also an innovation on the giant bomber, as the aircraft's relatively low cruise speed, of around 170mph, would mean that missions could last over 24 hours.

As far as weapons go, the XB-19 was designed to be bristling with guns, including a pair of 37mm cannons, which was totally unique among American bombers of WWII. In addition to these big anti-aircraft cannons, five .50 caliber and six .30 caliber machine guns would create a protective lead buffer around the aircraft.

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When it came to bombs, the XB-19 was an extremely heavy hitting aircraft for the time period, and was equipped with ten under-wing racks and a very large bomb bay. The bomb bay alone could hold a whopping 18,000lbs of bombs, and the under-wing racks could carry bombs of up to 2,000lbs each. The maximum bomb load for the XB-19 totaled an incredible 37,000lbs, although its 4,200 mile range would be noticeably shortened with such a heavy payload. By comparison, the B-17 Flying Fortress could carry around 8,500lbs of bombs on short-ranged missions, but usually carried half that on long range missions of Europe.

By the time the XB-19 finally flew in June of 1941, the aircraft was years behind its original schedule. Still, the hype around the giant bomber was palpable, and President Roosevelt even telephoned Donald Douglas himself to congratulate him on the accomplishment.

The single XB-19 continued test flights over California with relatively few issues throughout the remaining months of 1941, then Pearl Harbor was attacked in December 7th of that year. Due to fears of a Japanese strike on the west coast, the XB-19 had its gleaming skin painted matte green and machine guns were installed for its last few test flights before being transferred to Dayton, Ohio, a move aimed at keeping the big experimental bomber safe from possible marauding Japanese aircraft.

Out of about $1.5M that the Army had paid Douglas for the XB-19, Douglas had to come up with close to three times that amount out of its own coffers to keep the project afloat. The self funding of over-budget experimental aircraft of the war period was not uncommon, most notably was Howard Hughes' H-4 Hercules, otherwise known as the Spruce Goose, which cost the tycoon millions of his own money.

Test flights of the XB-19 continued for some time before it was apparent that although the aircraft was massive, and had impressive features, it was being surpassed by smaller bombers that could be built in greater numbers which had their development accelerated by America's entry into WWII. Thus, once testing was complete, the XB-19 was converted into a cargo aircraft and her engines were replaced with the production version of her original intended powerplant, the 2,600hp Allison V-3420-11 twenty four cylinder turbocharged engine. With this modification, her designation was changed to XB-19A, and her top speed was increased dramatically from 225mph to 275mph.

During the later part of WWII, the XB-19A used its heavy hauling ability to move high-priority material and people over long distances. Yet once the war was over, there was little demand for the expensive one-off heavy hauler. By the Summer of 1946 the giant aircraft that was once thought of as a cutting-edge new technology, had flown its last flight and was subsequently mothballed at Davis Monthan AFB in Arizona. By 1950, the aircraft had been dismembered and was eventually scrapped. Many lament the fact that this unique piece of aviation history was not preserved as a museum piece for future generations to enjoy.

Even though the XB-19 never entered production, the knowledge gained from its construction, testing and operation was incredibly valuable and was put to use in other strategic bomber and transport aircraft designs including the B-29 Superfortress and the B-36 Peacemaker. The B-36 would seize the record as America's largest flying bomber design when it first flew on August 8th, 1946, just days before the XB-19A's last flight.

Sources: here, here and here.

Tyler Rogoway is a defense journalist and photographer who maintains the website Foxtrot Alpha for Jalopnik.com You can reach Tyler with story ideas or direct comments regarding this or any other defense topic via the email address Tyler@Jalopnik.com