History
Background
In February 1935, the US Army Air Corps launched a top-secret initiative, Project D, to explore the feasibility of long-range bombers with unprecedented size and capabilities. Unlike typical development programs, Project D was purely experimental, intended to push the boundaries of current and emerging aviation technologies rather than result in a production aircraft. This mirrored the earlier Project A, which led to the Boeing XB-15, another experimental long-range bomber built as a prototype.
Two companies, Douglas Aircraft and Sikorsky, responded to the Army’s request for proposals. Douglas’s design was designated XBLR-2, and Sikorsky’s was XBLR-3. In October 1935, both companies were awarded contracts to create preliminary designs, test components, and prepare mockups. The Army’s ambitious timeline required prototype delivery by March 31, 1938.
By March 1936, both companies had completed mockups for inspection. After evaluation, the Army selected Douglas’s XBLR-2 for development, while Sikorsky was eliminated. Later that year, the Army replaced the BLR designation with the “B-for-Bomber” series, renaming the XBLR-2 as the XB-19. Progress on the XB-19 was hindered by funding shortages caused by the economic downturn, delaying its construction significantly. It wasn’t until 1938 that sufficient funds were allocated, allowing Douglas to resume work, although the project was already well behind schedule.
Design and Development
The XB-19 was a massive four-engine, low-wing monoplane featuring an innovative tricycle landing gear—marking the first instance of this configuration in an American bomber. The landing gear design was adapted from Douglas’s OA-4A Dolphin amphibian. Its airframe used an advanced all-metal, stressed-skin, flush-riveted construction, and the monocoque wings were so thick that engineers could crawl inside to conduct in-flight repairs.
Initially, the XB-19 was to be powered by four experimental 2,600-horsepower Allison XV-3420-1 liquid-cooled engines. However, development issues forced Douglas to substitute these with Wright R-3350-5 Duplex Cyclone radial engines, each rated at 2,000 horsepower. The aircraft carried 10,350 gallons of fuel internally, with optional auxiliary tanks adding another 824 gallons for extended range.
The XB-19’s bomb bay and underwing racks accommodated a massive payload. Internally, it could carry up to eight 2,000-lb bombs, sixteen 1,100-lb bombs, or thirty 600-lb bombs. The external racks could add another bomb of up to 2,000 lbs each, bringing the maximum bomb load to 37,100 lbs in an overload configuration. Defensive armament consisted of eleven machine guns (six .30-caliber and five .50-caliber) and two 37mm autocannons, though these weapons were not installed during its initial completion.
The XB-19’s crew complement was 16 personnel, with accommodations for additional mechanics and relief crews. Unique amenities included a dedicated compartment with seating, sleeping bunks, and even a galley for serving hot meals during long missions.
Construction Challenges and Testing
Construction delays plagued the XB-19 project. By the late 1930s, advancements in aviation technology had rendered the XB-19’s design outdated before it even took flight. Compounding this, Douglas faced competing priorities and even requested to cancel the project in 1938. However, the Army insisted on its completion, and the aircraft was finally finished in May 1941. The aircraft initially appeared in unpainted natural metal finish.
The XB-19’s public unveiling, following its removal from the classified list, was a media sensation. It was the largest American aircraft ever built, capturing public imagination as a symbol of American airpower. Initial taxi tests began in May 1941, but mechanical issues caused multiple delays. The XB-19 finally made its maiden flight on June 27, 1941, from Clover Field in Santa Monica. It underwent handling evaluations before being transferred to March Field for Army testing. The aircraft’s sheer size and innovative features captured public imagination, prompting President Franklin D. Roosevelt to send a congratulatory telegram to Donald Douglas.
Uneventful Operational Service and Modifications
Following the attack on Pearl Harbor in December 1941, the Army camouflaged the XB-19 in olive drab and gray paint and installed its full defensive armament. It underwent additional testing in California before being transferred to Wright Field, Ohio, in January 1942 to ensure its safety from potential Japanese air attacks.
During its evaluation, the XB-19 encountered engine cooling issues, which necessitated keeping the cooling gills open during long flights—reducing its maximum speed to 204 mph at 15,700 feet. The Army finally accepted the XB-19 into its operational service for future operations despite not having the engine problems addressed.
Following the XB-19’s flight trials in November 1942, the Army was unsure what to do with it as it was never intended to enter full-scale production. Ultimately, it was decided to convert the XB-19 into a cargo transport aircraft in the same manner as the Boeing XB-15. By 1943, during the conversion process, the Army wasted no opportunity to re-engine the aircraft with 2,600-hp Allison V-3420-11 turbocharged, 24-cylinder liquid-cooled engines. This solved the plagued cooling problems. However, being a cargo transport aircraft meant it lost armament, but, with new engines, the maximum speed was increased to 275 mph. After the conversion, the XB-19 was redesignated XB-19A.
The XB-19A conducted further testing and provided valuable data on airframe structures, equipment, and powerplant performance, influencing the development of future bombers like the B-29 and B-36. After its testing, the XB-19A operated as a cargo transport aircraft but saw limited use due to its size and impracticality for regular operations. It transferred between several airfields in Ohio, often occupying valuable ramp space. By 1945, the XB-19A’s operational importance had significantly diminished.
On August 17, 1946, the XB-19A made its final flight to Davis-Monthan Field in Arizona for retirement. Although originally intended for preservation, most of its airframe was scrapped by 1949. The only surviving remnants are its two massive main wheels, which are now displayed at the Hill Aerospace Museum at Hill Air Force Base, Utah, and the National Museum of the United States Air Force in Dayton, Ohio.
