The Boeing YB-40 Flying Fortress was a modified version of the B-17 Flying Fortress bomber, designed for operational testing.
This conversion transformed it into a heavily armed gunship. Its primary role was to defend other bombers during World War II missions.
When developers created the YB-40, long-range fighter planes like the North American P-51 Mustang were just beginning mass production. These fighters were not yet ready to escort bombers on long missions from England to Germany and return.
YB-40 Flying Hedgehog
In the early stages of the European bombing campaign in 1942 and 1943, Luftwaffe fighter pilots adopted a frontal attack strategy against American bombers.
They targeted the bombers’ “Twelve o’clock high” position, where defensive firepower was weakest.
This tactic aimed to disable a bomber by taking out its pilots and proved effective. At one point, a bomber crew only had a fifty-fifty chance of completing their 25-mission quota.
Without long-range fighter escorts available, the USAAF, the precursor to today’s U.S. Air Force, sought alternatives.
The USAAF initiated a project to create a “flying destroyer” or “flying hedgehog.” This aircraft would protect bombers by unleashing a barrage of machine-gun fire.
In August 1942, Vega Aircraft Corp. received a contract to transform the second production B-17F (aircraft no. 41-24341) into the first XB-40. This aircraft, more akin to a fighter than a bomber, lost its bombing capabilities, including the bomb bay and bombardier, and might have been more suitably classified with a “P” for “pursuit.”
Vega equipped the XB-40 with a chin-mounted nose turret, a feature later standard on B-17G models, and an extra Glenn L. Martin turret at the back of the dorsal cockpit fairing, replacing the radio operator’s single .50 caliber gun.
The waist gunners’ single .50s were upgraded to twin mounts. The ammunition supply was almost tripled from the standard B-17F, with 11,275 rounds compared to the B-17F’s 3,900 rounds.
USAAF Ordered 13 YB-40s for Service Testing
The XB-40, an experimental version of the B-17, made its debut flight on November 10, 1942. This was just a month before the introduction of the P-51B Mustang, powered by the Rolls-Royce Merlin engine, which would later provide bomber protection using different tactics.
Following the XB-40, the USAAF ordered 13 YB-40s for service testing. These aircraft, similarly equipped with heavy armament, were designed to escort bombers throughout their entire missions.
The USAAF quickly dispatched these YB-40s to Europe. One, aircraft no. 43-5732, faced an emergency landing in a Scottish peat bog during its transfer from Iceland to Great Britain in May 1943 due to fuel depletion. Although recovered, this aircraft was never operationally used.
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The rest of the YB-40s were integrated into the 92nd Bombardment Group in East Anglia, starting May 8, 1943. Led by Col. William M. Reid, the 92nd was a part of the extensive Eighth Air Force. The force eventually included 350,000 men across several bomb groups and air divisions.
YB-40 Triple the Ammunition Load
Reid found the modified bombers, now with fourteen .50-caliber Browning M2 machine guns, cumbersome. The YB-40s, laden with triple the normal ammunition load and additional gun turrets, were heavy and unwieldy. Their 27-foot ammunition belts were believed to be the origin of the term “the whole nine yards.
The YB-40s first saw action over Germany with the 92nd on May 29, 1943. However, they encountered no significant air combat.
On the return flight, the standard B-17s, relieved of their bomb load, outpaced the ammunition-laden, drag-heavy YB-40s. The YB-40s, slower and more vulnerable, became more of a liability than an asset in the fight against German fighters.
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At the outset of their deployment, Col. Reid urgently recommended to Washington that no further YB-40s be sent to the European Theater.
Ultimately, the series comprised 20 planes, including four unarmed TB-40 trainers, but the dozen that reached Europe only flew about ten missions. These YB-40s were later reverted to the standard B-17F configuration.
Post-World War II, a story emerged through writers like Martin Caidin and Glenn Infield, featured in men’s adventure magazines. It narrated how 1st Lt. Harold Fischer from the Fifteenth Air Force in Italy supposedly borrowed a YB-40 from the Eighth Air Force.
He aimed to trap Lt. Guido Rossi, an Italian pilot reportedly using a captured P-38 Lightning with U.S. markings to ambush returning bombers. Fischer allegedly enticed Rossi, who was unfamiliar with the YB-40’s heavy armaments, into an aerial battle and shot him down.
Survived the War
Both pilots reportedly survived the war, and the story claimed they later met. It also suggested Fischer died in the 1948 Berlin airlift, and in one version, Rossi romantically pursued Fischer’s widow. However, there’s no record of a YB-40 in Italy or a Fischer among Berlin Airlift casualties.
The only kernel of truth might be an Italian pilot, Lt. Angelo Tondi, using a captured P-38 to deceive U.S. bomber crews, casting doubt on the YB-40 story’s authenticity.
The YB-40’s specifications closely mirrored those of the B-17F, with a wingspan of 103 feet 9 inches, a service ceiling of 29,800 feet, and powered by four Wright R-1820-65 Cyclone radial engines, each offering 1,200 horsepower. It required a nine-person crew.
An attempt to transform the B-24 Liberator into a bomber-escort gunship proved futile. In February 1943, the XB-41 Liberator, heavily armed, began trials at Eglin Field, Florida.
Early tests, including weapon firing, showed promise, but there was no comprehensive assessment to check if the weightier XB-41 could match a Liberator formation’s pace. The AAF was still reviewing the XB-41 when the YB-40s’ inefficacy in combat became clear.
The Game Changed
By November 1943, the game had changed with the 354th Fighter Group’s arrival in England, operating the P-51B Mustang, later replaced by P-51D and P-51K models.
The Mustang’s introduction was a game-changer, offering enough range to escort bombers and excelling in air combat. It presented the Luftwaffe with a formidable challenge, far surpassing any modified, gun-laden bomber.
As air warfare tactics over Europe progressed, Mustangs could advance far ahead of bomber fleets, engaging German fighters long before they reached their targets.
The Mustang effectively countered the German air force, making it nearly impossible for German fighters to approach bombers closely enough for B-17 gunners to engage in combat during the war’s final year.