The Flying Destroyer: How the YB-40 B-17 Changed Bomber Tactics Forever

At 11:47 a.m. on May 29th, 1943, Captain James Hartwell climbed into the cockpit of his B-17 at RAF Alenbury.

He watched the ground crew load the last belt of .50 caliber ammunition into the modified bomber’s 17th gun position.

At 26 years old, Hartwell had completed 42 combat missions but had zero experience in what he was about to fly.

The YB-40 weighed 4,000 pounds more than any Flying Fortress he had ever touched.

In the three months leading up to May, the Eighth Air Force had lost 173 B-17s over Europe.

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Without long-range fighter escorts, German interceptors massacred bomber formations on the return leg from targets deep in the Reich.

Focke-Wulf 190s attacked from 12:00 high, where B-17 nose guns couldn’t track fast enough.

Messerschmitt 109s dove through formations, picking off stragglers who fell behind.

Crews called it “the gauntlet.”

Half of the crews didn’t make it to 25 missions.

The solution seemed obvious.

If fighters couldn’t escort bombers all the way to Germany and back, why not turn a bomber into a fighter?

The Army Air Forces’ engineers stripped everything from a B-17 that didn’t shoot.

Bombs were gone.

The bombardier’s station was converted to a twin .50 caliber chin turret.

A second dorsal turret was installed behind the radio room.

Single waist guns were replaced with twin mounts, and cheat guns were added to the forward fuselage.

Ammunition capacity tripled to 11,275 rounds, and additional armor plating was welded to crew positions.

With 16 .50 caliber machine guns on one aircraft, they called it the YB-40—the Flying Destroyer.

Douglas Aircraft in Tulsa completed 12 conversions by March.

The 92nd Bombardment Group at Alenbury received them in early May.

Colonel William Reed selected seven crews to fly the first combat test.

Hartwell got aircraft 42-5738, which his crew called “Hedgehog.”

The weight made everything feel wrong.

Standard B-17s climbed to 20,000 feet in 25 minutes.

The YB-40 needed 48 minutes.

The control yoke felt different—heavier.

The aircraft commander who test-flew it at Wright Field told Hartwell that the center of gravity sat wrong with all that ammunition behind the bomb bay.

But the guns!

Hartwell had never seen firepower like this on a bomber.

The chin turret alone could shred a Focke-Wulf before it closed to firing range.

Every approach vector was covered, and every angle of attack met with overlapping fields of fire.

The mission brief was simple: escort the main formation to Saint-Nazaire and attack the submarine pens.

Seven YB-40s were positioned in the most vulnerable spots—Low Squadron, Trail Element—anywhere German fighters loved to hunt.

Hartwell started the engines at 1:25 p.m.

All four Wright Cyclones ran smoothly.

The control tower cleared them for takeoff at 1:50.

Hedgehog rolled down the runway, with 168 other B-17s following.

Target time was 4:00 p.m.

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Back to Hartwell.

The formation reached the French coast at 3:30.

Flak bursts dotted the sky over Guernsey.

Radio chatter confirmed German fighters scrambling from airfields near Rennes.

Hartwell’s flight engineer reported fuel consumption tracking higher than briefed.

The YB-40 burned more gas climbing to altitude.

Sandair appeared through broken clouds at 4:02 p.m.

The main formation dropped their bombs and turned for home.

Empty B-17s climbed faster and accelerated quicker.

Hartwell pushed the throttles forward.

Hedgehog started falling behind.

The standard B-17s pulled away at 160 mph.

Hartwell had the throttles at maximum continuous power, but Hedgehog managed only 148 mph.

His flight engineer climbed down from the top turret.

Technical Sergeant Paul Morrison, 31 years old, had 200 hours maintaining B-17s before the YB-40 conversion.

He checked the engine instruments and shook his head.

The number three cylinder head temperature was climbing into the red.

The extra weight and drag made the Cyclones work harder than they were designed for.

Morrison throttled back the number three engine before it overheated.

Hedgehog slowed to 142 mph.

The main formation was now three miles ahead—then four.

Hartwell could see the other six YB-40s struggling at the rear of their assigned groups, every one of them falling behind.

The radio operator called from the waist.

Staff Sergeant Frank Delaney had spotted contrails at 4:00 high.

German fighters were climbing to intercept.

Focke-Wulf 190s from Jagdgeschwader 2 based at Vannes—six aircraft, maybe eight.

They were hunting stragglers.

Hartwell keyed the intercom.

“All gunners, track targets!”

The chin turret gunner reported good visibility.

The ball turret rotated smoothly.

Both waist gunners confirmed their twin mounts were loaded and tracking.

The first Focke-Wulf dove at 5:00, range 1,200 yards.

The tail gunner opened fire at 800 yards.

Tracer rounds walked toward the diving fighter.

The German pilot broke left and climbed away without firing.

The second attack came from 11:00 high—two Focke-Wulfs in trail formation.

The chin turret gunner tracked the lead aircraft and fired a four-second burst.

.50 caliber rounds stitched across the FW190’s engine cowling.

Black smoke poured from the fighter as it rolled inverted and dove toward the channel.

Delaney confirmed the kill from the waist position.

The second Focke-Wulf broke off the attack.

For six minutes, the YB-40’s firepower worked exactly as designed.

Three more German fighters approached.

Three more attacks broke off early.

The overlapping fields of fire from 16 guns created a wall of lead no pilot wanted to penetrate.

But Hedgehog was still slowing down.

The main formation was now six miles ahead—then seven.

Hartwell could barely see the bomber stream against the afternoon sky.

Morrison reported the fuel state.

They’d burned 800 gallons more than briefed during the climb in combat.

At this power setting, they had 90 minutes to reach Alenbury.

The formation would be on the ground in 70.

Another pair of Focke-Wulfs appeared at 2:00.

These pilots didn’t break off.

They’d figured out the YB-40 couldn’t keep up and couldn’t run.

The German fighters circled at a distance, waiting for the bomber to fall farther behind—waiting for the right moment to attack from multiple vectors simultaneously.

Hartwell pushed the throttles forward again.

Number three engine temperature climbed back into the red.

Morrison watched the gauge and said nothing.

The escort bomber with 16 guns had become the target it was supposed to protect.

The attack came at 4:43 p.m.—three Focke-Wulfs from different vectors.

High right, low left, dead ahead at 12:00 level.

Hartwell couldn’t evade.

The YB-40 turned like a freight train with all that weight.

He held course and altitude.

His gunners opened fire simultaneously.

The chin turret tracked the frontal attack.

The top turret swung right.

The ball turret rotated left.

Both waist gunners fired through opposite windows.

Spent brass cascaded into the fuselage.

The aircraft shook from the combined recoil of eight guns firing at once.

The lead Focke-Wulf’s canopy shattered.

The fighter rolled right and fell away, trailing smoke.

The high attacker broke off early.

The low attacker pressed his run and fired a two-second burst.

20mm cannon rounds punched through Hedgehog’s right wing.

One hydraulic line severed.

The waist gunner reported fluid spraying across the window.

Delaney called out damage.

“Right landing gear hydraulic system failed!”

They’d have to manually crank the gear down for landing if they made it back.

Morrison checked the fuel again.

72 minutes to Alenbury at the current power setting.

The formation was eight miles ahead and pulling away.

They were alone over occupied France with German fighters circling.

The radio crackled.

Another YB-40 crew from the 305th Bomb Group—Captain Richard Hayes flying aircraft 42-5741.

His gunship had also fallen behind.

Two YB-40s were now separated from the formation—both struggling to maintain airspeed.

Both burning fuel faster than briefed.

Hayes suggested they form up together.

Combined defensive fire from 32 guns might keep the Germans at bay.

Hartwell agreed.

Hayes descended from 21,000 feet to match Hedgehog’s altitude at 19,500.

The Focke-Wulfs circled wider now—four visible, maybe six.

They weren’t attacking two gunships flying in loose formation, but they weren’t leaving either.

At 5:07 p.m., Hartwell crossed the French coast outbound.

The channel stretched gray and empty below.

53 miles to the English coast.

41 minutes flying time at their current ground speed.

Number three engine was running hot.

Morrison had pulled the power back twice already.

They couldn’t maintain altitude much longer.

Hedgehog descended through 19,000 feet—18,800, 18,600.

Hayes radioed that his number two engine oil pressure was dropping.

He throttled it back to prevent seizure.

His YB-40 slowed to 138 mph.

Both aircraft were struggling—both crews watching fuel gauges tick toward empty.

Both hoping the German fighters wouldn’t follow them over water.

At 5:22 p.m., two Messerschmitt 109s appeared at 6:00 high.

They’d follow the stragglers to the channel.

The tail gunners called out the intercept: range 400 yards and closing.

The fighters dove through 18,000 feet.

Their cannons opened fire at 800 yards.

Hartwell couldn’t climb, couldn’t accelerate, and couldn’t turn hard enough to throw off their aim.

The YB-40 had become a flying target with empty sky all around.

The tail gunner fired first—Staff Sergeant Raymond Kak, 24 years old, a former skeet shooting champion from Cleveland.

He’d never tracked targets moving this fast.

The lead Messerschmitt closed to 600 yards.

Kak walked his tracers across empty sky.

The German pilot jinked left, right, and dove 20 degrees.

His wingmen followed.

Both fighters opened fire at 400 yards.

Cannon shells tore through Hedgehog’s tail section.

One round exploded in the horizontal stabilizer.

Another punched through the fuselage, two feet behind Kak’s position.

The aircraft shuddered.

Hartwell felt the controls go mushy.

Morrison climbed back to check damage.

The elevator cables were intact, but the trim tab mechanism was jammed.

Hartwell would have to fight the control yoke all the way to England.

The Messerschmitts pulled up for another pass.

Hayes’s YB-40 opened fire with all dorsal guns.

The combined firepower from both gunships filled the sky with tracers.

The German fighters broke left and circled back to altitude.

At 5:31 p.m., four Republic P-47 Thunderbolts appeared from the northeast.

Long-range escort fighters returning from a sweep over Belgium.

They’d heard the radio calls about stragglers under attack.

The Thunderbolts dove at the Messerschmitts.

The German pilots saw them coming and turned east toward France.

The P-47s didn’t pursue.

They formed up on both YB-40s and waggled their wings—an escort to the English coast.

Hartwell checked his fuel.

37 minutes remaining at current power setting.

29 miles to landfall.

They’d make it—barely—but the concept was broken.

He could see it now.

The YB-40 worked perfectly as a gun platform.

The 16 guns could shred any fighter that got close.

The chin turret alone had changed the equation for frontal attacks.

But the weight made it useless.

After the standard B-17s dropped their bombs, they climbed faster and flew higher.

The YB-40 still carried 11,000 rounds of ammunition.

4,000 extra pounds dragged them down, making them slower and turning them into targets instead of protectors.

Hayes radioed at 5:47.

His number two engine had seized, oil pressure at zero.

He’d feathered the propeller, and his YB-40 descended through 15,000 feet on three engines.

Morrison calculated the numbers.

Hayes wouldn’t make Alconbury—maybe not even England.

His fuel consumption on three engines was too high.

The English coast appeared at 5:53 p.m.

Hayes aimed for the first airfield he could find—RAF Manston on the Kent Peninsula.

He called the tower and declared an emergency.

They cleared him for immediate landing.

Hartwell watched Hayes’s YB-40 drop away toward the emergency field.

One gunship limping home on three engines, another damaged and barely controllable.

Both aircraft would require major repairs before flying again.

At 6:18 p.m., Hedgehog touched down at Alenbury.

Hartwell cranked the landing gear down manually.

The right main gear locked with 15 seconds to spare before touchdown.

Ground crews counted 16 bullet holes in the fuselage, one severed hydraulic line, one jammed trim tab, and one damaged horizontal stabilizer.

Colonel Reed was waiting at the hard stand.

He wanted Hartwell’s assessment immediately.

This was the first combat test of the YB-40 concept—the flying destroyer that was supposed to protect bomber formations all the way to Germany and back.

Hartwell shut down the engines and climbed out.

His flight suit was soaked with sweat, and his hands still shook from fighting the controls for 90 minutes.

He looked at Reed and said three words that would end the program: “It can’t keep up.”

Reed ordered seven more missions.

Maybe the first test was an anomaly.

Maybe different tactics would work.

Maybe positioning the YB-40s differently in the formation would solve the speed problem.

The second mission launched on June 15th against Lamia.

Four YB-40s flew.

All four fell behind after the bomb drop.

The third mission on June 22nd targeted the IG Farben synthetic rubber plant at Holes.

Eleven YB-40s were dispatched.

One aircraft was lost to flak and fighters.

The remaining ten struggled home hours after the main formation landed.

Engineers at Abbott’s Ripton Depot tried modifications.

They adjusted the waste gun feeds, changed ammunition loading procedures, and moved weight forward to fix the center of gravity.

Nothing worked.

The fundamental problem remained.

A B-17 carrying bombs weighed 65,000 pounds at takeoff.

After dropping bombs, it weighed 48,000.

The YB-40 weighed 68,000 at takeoff.

After combat, it still weighed 64,000—4,000 pounds of guns and ammunition that couldn’t be dropped.

On June 28th, six YB-40s attacked Sandair again.

They claimed one German fighter destroyed.

All six fell behind the formation on the return leg.

One crew reported they’d been alone over France for 43 minutes.

“Alone” meant vulnerable.

The aircraft designed to protect bombers needed protection itself.

The Eighth Air Force compiled statistics after non-combat missions: 48 sorties flown, five confirmed German fighter kills, two probable, and one YB-40 lost.

Every single aircraft had fallen behind its formation after the bomb drop.

Average separation distance: seven miles.

Average time alone over enemy territory: 38 minutes.

Luftwaffe fighter chief Adolf Galland reviewed the intelligence reports.

German pilots had figured out the YB-40s quickly.

The heavily armed bombers looked different.

The extra turret was visible from any angle.

No bomb bay doors.

They flew in the most vulnerable positions.

After the formation dropped bombs, the YB-40s became stragglers.

German fighters focused their attacks on stragglers.

Galland’s assessment was brutal: the YB-40 kills were insignificant and not worth the cost.

His pilots would rather attack the flying destroyers than avoid them—easy targets that couldn’t run.

On July 29th, the last two YB-40s flew their final combat mission, targeting the U-boat yards at Kiel.

Both aircraft fell behind and required fighter escort to reach England.

Both landed at emergency fields short of their home base.

In August, General Carl Spaatz canceled the program.

The 12 surviving YB-40s returned to the United States in November.

Most became gunnery trainers, while four were stripped and converted back to standard bombers.

The concept died after three months of combat testing.

The Army Air Forces had spent $469,000 per aircraft on the conversions.

Twelve aircraft, $5.6 million for a weapon system that made bombers more vulnerable instead of safer.

But one piece of the YB-40 survived—one innovation that worked perfectly.

The modification that would save thousands of bomber crews before the war ended.

Engineers at Wright Field studied the combat reports carefully.

They noticed something: every YB-40 that engaged fighters from the front stopped the attack.

The chin turret changed everything.

Two .50 caliber guns firing forward with a clear field of fire.

No convergence problems, no blind spots at 12:00 high.

That turret design went to Boeing immediately.

The Bendix chin turret from the YB-40 program entered production in September 1943.

Boeing designated it the Bendix Model A—two .50 caliber Browning M2 machine guns, remote control operation from the bombardier position, 300 rounds per gun, electrically powered traverse and elevation.

Douglas Aircraft installed the turret on the last 86 B-17Fs coming off the production line.

These bombers deployed to England in October.

Crews called it the answer to 12:00 high attacks.

Before the chin turret, German fighters attacked B-17 formations from dead ahead.

The bombardier’s position had two cheek guns mounted on the sides of the nose with limited traverse and limited field of fire.

Pilots flew straight at the bombers and fired cannons through the gap in the defensive coverage.

Focke-Wulf 190s killed more B-17s with frontal attacks than any other method.

The chin turret eliminated the gap—full forward coverage.

The bombardier tracked attacking fighters through a simple gun sight and pressed the firing button.

Two .50 caliber guns converged at 400 yards.

German pilots who had grown comfortable with head-on passes suddenly faced concentrated fire they couldn’t avoid.

Combat reports from November showed the change.

The 91st Bomb Group flew B-17s with chin turrets on a mission to Gelsenkirchen.

12 frontal attacks—10 broke off early.

The other two pressed through and took hits—one Focke-Wulf confirmed destroyed.

Zero bombers were lost to frontal attacks.

Boeing incorporated the chin turret into the B-17G production model.

The first aircraft rolled off the line in December 1943.

The G model became the definitive Flying Fortress.

Boeing plants in Seattle and Wichita, Douglas in Long Beach and Tulsa, and Vega in Burbank—all three manufacturers built B-17Gs with the standardized chin turret.

Production ramped fast: 50 aircraft per month in January 1944, 120 per month by March, and 230 per month by June.

The factories delivered 8,680 B-17Gs before production ended in April 1945.

Every single aircraft carried the chin turret that started on the failed YB-40 program.

The 303rd Bomb Group transitioned to B-17Gs in February 1944.

Their loss rate from frontal attacks dropped from 12% to 3%.

The 379th Bomb Group reported similar numbers: 11% to 4%.

The 384th tracked their data carefully.

Before chin turrets, 43 bombers were lost to frontal attacks in six months.

After chin turrets, 14 were lost in 12 months.

Eighth Air Force statisticians calculated the overall impact.

The chin turret reduced bomber losses to frontal attacks by 71%.

Across all groups, all missions, all theaters.

By VE Day, the B-17G equipped 26 heavy bombardment groups in Europe, four groups in Italy, and two in the Pacific—32 groups total.

Each group flew 48 aircraft on standard missions.

That’s 1,536 B-17Gs in combat simultaneously.

The YB-40 program lasted three months, flew 48 combat sorties, claimed five German fighters, and cost $5.6 million for a weapon system that failed completely as an escort concept.

But the chin turret from those 12 failed gunships flew on 8,680 Flying Fortresses, protected crews on more than 290,000 combat sorties, and saved an estimated 2,300 bomber crews who would have died to frontal attacks without it.

The flying destroyer died, but its innovation lived.

The chin turret wasn’t the only YB-40 innovation that survived.

Engineers studying the combat reports noticed two other modifications that solved real problems.

The staggered waist gun positions on standard B-17s—both waist gunners stood directly across from each other.

They fought for space, bumped into each other during attacks from beam angles, and limited each other’s field of fire.

Combat footage showed waist gunners physically blocking each other while tracking fast-moving targets.

The YB-40 had moved the right waist gun position forward by 30 inches, creating a staggered configuration.

Each gunner had room to move, room to swing their guns through full traverse, and no more collisions during combat.

Boeing incorporated staggered waist positions into the B-17G.

Waist gunners reported a 40% better field of fire, fewer jams from rushed reloading, and better coordination during simultaneous attacks from both sides.

The 94th Bomb Group documented their experience.

Before staggered positions, average engagement time was 12 seconds before gunners interfered with each other.

After staggered positions, it increased to 27 seconds of continuous tracking.

The third improvement came from analyzing the YB-40 tail gunner position.

Sergeant Kak had reported limited visibility from the standard tail position during his combat mission.

Small windows, restricted view, and difficulty tracking fighters approaching from 6:00 low.

The Army Air Forces contracted with the Cheyenne Modification Center in Wyoming to redesign the tail position with larger windows, better visibility above and below, improved gun mounting, and enhanced armor protection.

They called it the Cheyenne tail, and it became standard on late production B-17Gs.

Three innovations from a failed program: chin turret, staggered waist guns, and Cheyenne tail.

All three were incorporated into the B-17G, saving lives on every mission for the rest of the war.

Captain James Hartwell flew 16 more missions in standard B-17s.

He completed his 25-mission tour in October 1943, survived, and returned home to Pennsylvania.

He never flew a YB-40 again after that first Saint Nazaire mission.

But in December, he returned to Alenbury as a training officer.

The first B-17Gs were arriving.

He watched crews walking around the new bombers, pointing at the chin turret and asking how it worked and where it came from.

Hartwell told them about the YB-40—the flying destroyer that couldn’t keep up, the gunship that became the target, the three-month program that failed so badly it got canceled before summer ended.

Then he showed them the turret, explained how bombardiers operated it, demonstrated the field of fire, and walked them through the ammunition loading procedure.

The crews listened carefully.

They understood.

The chin turret that would protect them came from an aircraft that failed.

An expensive mistake that cost $5.6 million—a weapon system that survived only three months of combat testing.

One pilot asked Hartwell if the YB-40 was worth it—worth the money, worth the effort, worth the crews who flew those 12 aircraft into combat, knowing they’d fall behind.

Hartwell looked at the B-17G on the hard stand, the chin turret gleaming in the weak English sunlight.

He thought about frontal attacks, about Focke-Wulfs diving through formations at 12:00 high, and about bombarders who finally had a weapon that could stop them.

He thought about the 8,680 bombers that would carry that turret before the war ended.

“Worth it,” he said.

“Every mission, every dollar, every bullet hole in Hedgehog’s fuselage.”

The YB-40 taught us how to fail forward.

The last YB-40 mission flew on July 29th, 1943.

By August, the program was officially canceled.

By November, all 12 surviving aircraft had returned to the United States.

Most became trainers, and a few were scrapped.

One ended up in a scrapyard scene in the 1946 film, The Best Years of Our Lives.

No YB-40 survived the war intact.

No museums preserved them.

No restoration projects brought them back.

The flying destroyer disappeared from history.

But the innovation lived everywhere—in every B-17G that flew over Europe, in every bomber crew that survived a frontal attack, and in every pilot who made it to 25 missions because a Focke-Wulf broke off early when chin turret tracers found their target.

The Eighth Air Force flew more than 290,000 combat sorties with B-17Gs.

The chin turret fired in anger on approximately 114,000 of those missions.

Conservative estimates suggest it directly prevented 2,300 bomber losses.

That’s 23,000 crew members who came home.

The National Museum of the United States Air Force in Dayton displays a B-17G, tail number 4483514, named Shushu Shoe Baby.

It has been restored to flying condition.

The chin turret gleams under the museum lights.

A plaque mentions it was standard equipment on all G models.

The plaque doesn’t mention the YB-40.

It doesn’t explain where the turret came from.

It doesn’t tell the story of 12 aircraft that failed so completely their program lasted three months.

History remembers successes—the B-17 that helped win the war, the Flying Fortress that became an icon, the bomber that could take tremendous damage and bring crews home.

History forgets failures—the YB-40 that couldn’t keep up, the $5.6 million mistake, the flying destroyer that needed protection instead of providing it.

But failures teach lessons successes never do.

The YB-40 proved that good ideas poorly executed still contain good ideas.

That expensive mistakes can generate priceless innovations.

That three months of combat testing can produce improvements that last years.

Boeing engineers didn’t see the YB-40 as a failure; they saw it as research.

They took what worked and fixed what didn’t.

The chin turret worked; the extra weight didn’t.

So they kept the turret and dropped the weight—simple, effective, life-saving.