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Boeing YB-40 Flying Fortress

United States (1943)
Picture of Boeing YB-40 Flying Fortress Bomber Escort Prototype Aircraft
Picture of Boeing YB-40 Flying Fortress Bomber Escort Prototype Aircraft

The YB-40 Flying Fortress was a wartime conversion of the classic B-17 bomber to fulfill a flying gunship role - 25 were built.


Detailing the development and operational history of the Boeing YB-40 Flying Fortress Bomber Escort Prototype Aircraft.  Entry last updated on 10/23/2017. Authored by Staff Writer. Content ©www.MilitaryFactory.com

Like other classic aircraft of the World War 2 period (1939-1945), the Boeing B-17 "Flying Fortress" heavy bomber was subject to many experiments and conversion projects during its time in service. The YB-40 was developed as one of the former and intended to showcased the B-17 as a sort of flying "gun bus" to defend bomber formations to-and-from enemy targets. The project was not an outright success but did yield some twenty-five examples before the end and influence several key changes of the B-17 line going forward.

Prior to the availability of long-range fighter escorts like the North American P-51 Mustang and Republic P-47 Thunderbolt, thought was given to outfitting bomber airframes with additional machine guns, suitable ammunition stocks, and improved armor protection to help them serve as formation escorts. These aircraft were designed to accompany large American bomber formations over enemy airspace, provide point defense against intercepting enemy fighters, and return with the formation once the war load was dropped on enemy targets below. The B-17 seemed a good a starting point as any for it was a proven player and available in the numbers required.

Project V-139 marked the first example of such a creation and this involved a production-quality B-17F model. Lockheed (Vega) handled the early conversion work which involved addition of machine guns at various key locations and armor protection at the gunner's positions. The single guns at each open-air beam position (the openings staggered for better gunner movement in the heat-of-battle) was doubled and a second dorsal turret was added aft of the first. A twin-gunned Bendix powered turret was installed at the chin position. The bombing equipment and bomb bay were deleted and, in the latter's place, a reserve for additional stocks of ammunition was added. The Sperry ball turret under the belly was retained and the cheek machine guns, at the sides of the forward fuselage, were still in play (though not initially installed as part of the conversion work).
The aircraft could carry as many as thirty heavy machine guns if pressed though between fourteen and eighteen proved typical due to the weight gains and practicality. With each gun installation there was an increase in ammunition required and a standard load of nearly 11,000 rounds was seen - most of this dedicated to the two dorsal turrets and nose guns.

Douglas Aircraft was charged with making the modifications for the operational aircraft and, beyond the mentioned gun installations, other arrangements were trialed during this period - some involving automatic cannons of various calibers - though none made it to service.

The product was already on order back in October 1942 when a prototype "XB-40" made a first-flight on November 10th of that year. The USAAF required thirteen converted bombers through an initial batch and a further twelve were added in January of 1943. First production-quality aircraft emerged from Douglas that March and the series carried the developmental designation of "YB-40" for the interim, pending the outcome of their in-service performance.

The aircraft were delivered to England in May of 1943 (one was lost en route, crash-landing in Scotland) and these flew operational-level missions for the USAAF from that point until July of that year. Results were not wholly impressive as the fleet claimed only five enemy fighters from the forty-eight missions flown. The added weight of the armor plate and installed armament meant that these defenders could not keep pace with the main bomber force once the bombers had dropped their war loads. The test program was ended with the last mission flown on July 29th, 1943, this an attack involving a pair of XB-40s on the Kiel submarine pen.

Once their operational usefulness had concluded, the stock was sent back stateside and took part in crew training as the "TB-40". All were scrapped before the end of the war in 1945. The XB-40 was not a total loss as it introduced several key features of future B-17 generations - namely the Bendix chin turret (which proved vital in defending against oncoming attacks from the front) and the staggered beam gun positions. Work on the XB-40 also resulted in upgrades to the tail gunner's position in the way of improved vision for better tracking and engagement of fast-moving targets.

As completed, the YB-40 could boast a maximum speed of 292 mph with a cruise speed of 195 mph. Range was out to 2,260 miles with a service ceiling of 29,200 feet. Power was from 4 x Wright R-1820-65 turbosupercharged air-cooled radial piston engines developing 1,200 horsepower each.






Our Data Modules allow for quick visual reference when comparing a single entry against contemporary designs. Areas covered include general ratings, speed assessments, and relative ranges based on distances between major cities.

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Relative Maximum Speed Rating
Hi: 300mph
Lo: 150mph
    This entry's maximum listed speed (292mph).

    Graph average of 225 miles-per-hour.
City-to-City Ranges
NYC
 
  LON
LON
 
  PAR
PAR
 
  BER
BER
 
  MOS
MOS
 
  TOK
TOK
 
  SYD
SYD
 
  LAX
LAX
 
  NYC
Graph showcases the Boeing YB-40 Flying Fortress's operational range (on internal fuel) when compared to distances between major cities.
Aviation Era
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Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units
25
25


  * Commercial Market High belongs to Cessna 172.

  ** Military Market High belongs to Ilyushin Il-2.


Altitude Visualization
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Origin: United States
Year: 1943
Type: Bomber Escort Prototype Aircraft
Manufacturer(s): Boeing Company - USA
Production: 25
Status: Retired, Out-of-Service
Global Operators:
United States (limited)
Historical Commitments / Honors:

Military lapel ribbon for Operation Allied Force
Military lapel ribbon for the Arab-Israeli War
Military lapel ribbon for the Battle of Britain
Military lapel ribbon for the Battle of Midway
Military lapel ribbon for the Berlin Airlift
Military lapel ribbon for the Chaco War
Military lapel ribbon for the Cold War
Military lapel ribbon for the Cuban Missile Crisis
Military lapel ribbon for the Falklands War
Military lapel ribbon for the French-Indochina War
Military lapel ribbon for the Golden Age of Flight
Military lapel ribbon for the 1991 Gulf War
Military lapel ribbon for the Indo-Pak Wars
Military lapel ribbon for the Iran-Iraq War
Military lapel ribbon for the Korean War
Military lapel ribbon for the 1982 Lebanon War
Military lapel ribbon for the Malayan Emergency
Military lapel ribbon for the attack on Pearl Harbor
Military lapel ribbon for the Six Day War
Military lapel ribbon for the Soviet-Afghan War
Military lapel ribbon for the Spanish Civil War
Military lapel ribbon for the Suez Crisis
Military lapel ribbon for the Vietnam War
Military lapel ribbon for Warsaw Pact of the Cold War-era
Military lapel ribbon for the WASP (WW2)
Military lapel ribbon for the World War 1
Military lapel ribbon for the World War 2
Military lapel ribbon for the Yom Kippur
* Ribbons not necessarily indicative of actual historical campaign ribbons. Ribbons are clickable to their respective campaigns/operations.
Measurements and Weights icon
Structural - Crew, Dimensions, and Weights:
Unless otherwise noted the presented statistics below pertain to the Boeing YB-40 Flying Fortress model. Common measurements, and their respective conversions, are shown when possible.

Operational
CREW


Personnel
10


Dimension
LENGTH


Feet
73.82 ft


Meters
22.5 m


Dimension
WIDTH


Feet
103.35 ft


Meters
31.5 m


Dimension
HEIGHT


Feet
19.03 ft


Meters
5.8 m


Weight
EMPTY


Pounds
55,116 lb


Kilograms
25,000 kg


Weight
LOADED


Pounds
73,998 lb


Kilograms
33,565 kg

Engine icon
Installed Power - Standard Day Performance:
4 x Wright R-1820-65 turbosupercharged radial piston engines developing 1,200 horsepower each.

Performance
SPEED


Miles-per-Hour
292 mph


Kilometers-per-Hour
470 kph


Knots
254 kts


Performance
RANGE


Miles
2,262 mi


Kilometers
3,640 km


Nautical Miles
1,965 nm


Performance
CEILING


Feet
29,199 ft


Meters
8,900 m


Miles
5.53 mi

Supported Weapon Systems:

Graphical image of an aircraft medium machine gun
Graphical image of an aircraft heavy machine gun
Armament - Hardpoints (0):

Typical:
2 x 0.50 caliber Browning M2 heavy machine guns in powered Bendix chin turret.
1 x 0.50 caliber Browning M2 heavy machine gun in left cheek position.
1 x 0.50 caliber Browning M2 heavy machine gun in right cheek position.
2 x 0.50 caliber Browning M2 heavy machine guns in forward dorsal turret.
2 x 0.50 caliber Browning M2 heavy machine guns in aft dorsal turret.
2 x 0.50 caliber Browning M2 heavy machine guns in left beam position.
2 x 0.50 caliber Browning M2 heavy machine guns in right beam position.
2 x 0.50 caliber Browning M2 heavy machine guns in ventral Sperry ball turret.
2 x 0.50 caliber Browning M2 heavy machine guns in tail turret position.
Variants: Series Model Variants
• XB-40 - Prototype model deisgnation
• YB-40 - Base Series Designation; 25 examples completed.
• TB-40 - YB-40 gun bus aircraft reworked as trainers.