WWII

YB-40, The Flying .50 Cal Machine Gun Gunship

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.

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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 photo offers a great view of the port waist gun station, highlighting the twin .50 caliber guns mounted there. It's interesting to see the wind deflector just ahead of the opening and that the twin guns are positioned centrally in the window, unlike the more forward placement typical of single-gun setups.
This photo offers a great view of the port waist gun station, highlighting the twin .50 caliber guns mounted there. It’s interesting to see the wind deflector just ahead of the opening and that the twin guns are positioned centrally in the window, unlike the more forward placement typical of single-gun setups.

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.

Read More: The Swoose is the Oldest Surviving B-17 Flying Fortress

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.”

This interior shot of the YB-40, looking towards the front, showcases the upgraded dual waist gun setup. This model pioneered the staggered waist gun configuration in the Flying Fortress series. The image reveals modifications made to enhance the ammunition supply to the guns. Observe the substantial amount of ammunition on board and the measures taken to redistribute weight towards the front.
This interior shot of the YB-40, looking towards the front, showcases the upgraded dual waist gun setup. This model pioneered the staggered waist gun configuration in the Flying Fortress series. The image reveals modifications made to enhance the ammunition supply to the guns. Observe the substantial amount of ammunition on board and the measures taken to redistribute weight towards the front.

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.

This is an unusual view of the firepower on the Boeing YB-40, a heavily armed 'gunship'
This is an unusual view of the firepower on the Boeing YB-40, a heavily armed ‘gunship’

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.

Read More: B-17 5 Grand Had 35,000 Signatures on it

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.

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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.

The YB-40 could carry nearly triple the amount of ammunition
The YB-40 could carry nearly triple the amount of ammunition

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.

Read More: The XF-12 Rainbow was WWII’s SR-71 Blackbird

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.

Twenty-five B-17F aircraft were transformed into either YB-40s or TB-40s (gunnery training versions). This photo captures aircraft numbered 42-5732 through 42-5745, which arrived at the modification center in Tulsa during October and November of 1942 for their upgrades. The process of fitting the powered turret into the radio compartment is in progress.
Twenty-five B-17F aircraft were transformed into either YB-40s or TB-40s (gunnery training versions). This photo captures aircraft numbered 42-5732 through 42-5745, which arrived at the modification center in Tulsa during October and November of 1942 for their upgrades. The process of fitting the powered turret into the radio compartment is in progress.

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.

Read More: The Lethal Remote-Controlled B-17 & B-24 Bombers

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.

A significant advancement was fitting a Bendix remote turret beneath the Bombardier's spot, boosting frontal firepower. Both German and Japanese pilots had identified the Flying Fortress's weaker nose defenses and often targeted this area. The turret's effectiveness led Douglass to equip the last eighty-six B-17Fs with Bendix chin turrets, a feature that became standard across all three manufacturers with the B-17G model. This particular YB-40 lacks cheek guns for the Navigator, though they were added in later versions.
A significant advancement was fitting a Bendix remote turret beneath the Bombardier’s spot, boosting frontal firepower. Both German and Japanese pilots had identified the Flying Fortress’s weaker nose defenses and often targeted this area. The turret’s effectiveness led Douglass to equip the last eighty-six B-17Fs with Bendix chin turrets, a feature that became standard across all three manufacturers with the B-17G model. This particular YB-40 lacks cheek guns for the Navigator, though they were added in later versions.

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.

29,000 Feet

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.

The 92nd Bomb Group / 327th Bomb Squadron tested twelve YB-40s in combat, flying missions from May to July 1943. Pictured are "Woolaroc" (42-5743) and "Chicago" (42-5741), operating from RAF Alconbury. Both these aircraft are equipped with port cheek guns.
The 92nd Bomb Group / 327th Bomb Squadron tested twelve YB-40s in combat, flying missions from May to July 1943. Pictured are “Woolaroc” (42-5743) and “Chicago” (42-5741), operating from RAF Alconbury. Both these aircraft are equipped with port cheek guns.

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.

Read More: SB-17, Specialist B-17s Designed to Drop Rescue Boats

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.

The YB-40s were pulled out of the European Theater and reclassified as TB-40s for gunnery training roles in the United States. Pictured here is 42-5925 alongside four Bell P-63 King Cobras during a training flight.
The YB-40s were pulled out of the European Theater and reclassified as TB-40s for gunnery training roles in the United States. Pictured here is 42-5925 alongside four Bell P-63 King Cobras during a training flight.

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.