YB-40 Flying Fortress
The prototype XB-40 was a Boeing B-17F modified by Lockheed Vega (Project V-139) by converting the second production B-17F-1-BO (s/n 41-24341).
Role Bomber escort
Built by Lockheed-Vega
First flight 10 November 1942
Introduction 29 May 1943
Retired October 1943
Primary user United States Army Air Forces
Number built 25
Developed from Boeing B-17 Flying Fortress

The Boeing YB-40 Flying Fortress was a modification for operational testing purposes of the B-17 Flying Fortress bomber aircraft, converted to act as a heavily armed gunship to support other bombers during World War II. At the time of its development, long-range fighter aircraft such as the North American P-51 Mustang were just entering quantity production, and thus were not yet available to accompany bombers all the way from England to Germany and back.

Design and development

Close-up of the array of .50-caliber guns on the Boeing YB-40 Flying Fortress.
Close-up of the array of .50-caliber guns on the Boeing YB-40 Flying Fortress.

Work on the prototype, Project V-139, began in September 1942 by converting the second production B-17F-1-BO (serial number 41-24341) built. Conversion work was done by Lockheed's Vega company.

The aircraft differed from the standard B-17 in that a second manned dorsal turret was installed in the former radio compartment, just behind the bomb bay and forward of the ventral ball turret's location. The single .50-caliber light-barrel (12.7 mm) Browning machine gun at each waist station was replaced by two of them mounted side by side as a twin-mount emplacement, with a mount for each pair of these being very much like the tail gun setup in general appearance. The bombardier's equipment was also replaced by two .50-caliber light-barrel Browning AN/M2 machine guns in a remotely operated Bendix designed "chin"-location turret, directly beneath the bombardier's location in the extreme nose.[1]

The existing "cheek" machine guns (on the sides of the forward fuselage at the bombardier station), initially removed from the configuration, were restored in England to provide a total of 16 guns, and the bomb bay was converted to an ammunition magazine. Additional armor plating was installed to protect crew positions.[1]

The aircraft's gross weight was some 4,000 lb (1,800 kg) greater than a fully armed B-17. An indication of the burden this placed on the YB-40 is that while the B-17F on which it was based was rated to climb to 20,000 ft (6,100 m) in 25 minutes, the YB-40 was rated at 48 minutes. Part of the decreased performance was due to the weight increase, and part was due to the greater aerodynamic drag of the gun stations.[2]

The first flight of the XB-40 was on 10 November 1942. The first order of 13 YB-40s was made in October 1942. A follow-up order for 12 more was made in January 1943. The modifications were performed by Douglas Aircraft at their Tulsa, Oklahoma center, and the first aircraft were completed by the end of March 1943. Twenty service test aircraft were ordered, Vega Project V-140, as YB-40 along with four crew trainers designated TB-40.[2]

Because Vega had higher priority production projects, the YB-40/TB-40 assembly job was transferred to Douglas. A variety of different armament configurations was tried. Some YB-40s were fitted with four-gun nose and tail turrets. Some carried cannon of up to 40 mm in caliber, and a few carried up to as many as 30 guns of various calibers in multiple hand-held positions in the waist as well as in additional power turrets above and below the fuselage.[1]

Externally, the XB-40 had the symmetrical waist windows of the standard B-17F and the second dorsal turret integrated into a dorsal fairing. In contrast, most of the YB-40s had the positions of the waist windows staggered for better freedom of movement for the waist gunners, and the aft dorsal turret was moved slightly backwards so that it stood clear of the dorsal fairing.[2]

Operational history

World War II emblem of the 327th Bombardment Squadron, featuring characters (Alley Oop and Dinny) from the Alley Oop comic strip
World War II emblem of the 327th Bombardment Squadron, featuring characters (Alley Oop and Dinny) from the Alley Oop comic strip

The YB-40's mission was to provide a heavily armed escort capable of accompanying bombers all the way to the target and back. Of the initial order of 13, one (serial 43-5732) was lost on the delivery flight from Iceland to the UK in May 1943; it force-landed in a peat bog on a Scottish island after running out of fuel. Although removed to Stornoway and repaired, it never flew in combat. The remaining 12 were allocated to the 92d Bombardment Group (Heavy), being assigned to the 327th Bombardment Squadron, stationed at RAF Alconbury (AAF-102) on 8 May 1943.

YB-40s flew in the following operational missions:

Summary

Boeing YB-40 Flying Fortress, 42-5736 ("Tampa Tornado") on display at RAF Kimbolton, England, 2 October 1943 when it was shown to those attending a party for local children.
Boeing YB-40 Flying Fortress, 42-5736 ("Tampa Tornado") on display at RAF Kimbolton, England, 2 October 1943 when it was shown to those attending a party for local children.

Altogether of the 59 aircraft dispatched, 48 sorties were credited. Five confirmed and two probable German fighter kills were claimed, and one YB-40 was lost, shot down on 22 June mission to Hüls, Germany. Tactics were revised on the final five missions by placing a pair of YB-40s in the lead element of the strike to protect the mission commander.

The original design concept of the YB-40 never played out as intended in practice. Luftwaffe fighter chief Adolf Galland considered the gunship's handful of combat victories to be "insignificant" and not worth the cost of the aircraft.[3] The increased weight from the additional machine guns and ammunition nearly cut the YB-40's climb rate in half from that of a B-17F, and in level flight it had difficulty keeping up with standard Flying Fortresses, especially after they had dropped their bombs. Despite the overall failure of the project as an operational aircraft, it led directly to the Bendix chin turret's fitment on the last 65 (86 according to some sources)[4] Douglas-built aircraft starting with the B-17F-70-DL production block,[5][note 1] and were part of the standardized modifications conspicuous on the final production variant of the B-17, the B-17G:

Once the test program ended, most of the surviving aircraft returned to the U.S. in November 1943 and were used as trainers. 42-5736 ("Tampa Tornado") was flown to RAF Kimbolton on 2 October 1943 where it was put on display and later used as a group transport. It was returned to the United States on 28 March 1944. All of the aircraft were sent to reclamation, mostly at RFC Ontario in May 1945, being broken up and smelted. A couple of the YB-40s can be seen in the 1946 movie The Best Years of Our Lives, in the famous scene shot at the Ontario "graveyard". No airframes were sold on the civil market.

Operators

 United States
XB-40: Conversion of B-17F-1-BO 41-24342 (Not deployed to ETO)
YB-40: Conversions of B-17F-10-VE 42-5732; 5733, "Peoria Prowler"; 5734, "Seymour Angel"; 5735, "Wango Wango"; 5736, "Tampa Tornado"; 5737, "Dakota Demon"; 5738, "Boston Tea Party"; 5739, "Lufkin Ruffian"; 5740, "Monticello"; 5741, "Chicago"; 5742, "Plain Dealing Express"; 5743, "Woolaroc"; 5744, "Dollie Madison" (All deployed to ETO)
YB-40: Conversions of B-17F-35-VEs 42-5920, 5921, 5923, 5924, 5925, and 5927 (Not deployed to ETO)
TB-40: Conversions of B-17F-25-VEs 42-5833 and 5834; B-17F-30-VE 42-5872, and B-17F-35-VE 42-5926 (5833 deployed to ETO, but not used in combat; remainder stayed in the United States).

Specifications (YB-40)

Data from[citation needed]

General characteristics

Performance

Armament

Ammunition carried[citation needed]
Location Rounds
Nose 2,200
Front top turret 2,500
Aft top turret 3,300
Ball turret 300
Waist guns 1,200
Tail guns 1,200
Total 10,700

See also

Related development

References

Notes

  1. ^ Most sources say that the turret was introduced on the B-17F-75-DL, but photographic evidence indicates that the F-70-DL also had the turret.[6]

Citations

  1. ^ a b c Bishop 1986, pp. 69, 73, 246–247.
  2. ^ a b c Freeman 1991, pp. 154–155.
  3. ^ Levine 1992, p. 90.
  4. ^ Lyman, Troy (12 May 2003). "B17 — Queen of the Sky — The B-17F". b17queenofthesky.com. Troy Lyman's B-17 Flying Fortress Site. Retrieved 24 June 2014. "...factories were trying to fine a more effective solution to the B-17's lack of forward firepower...This solution was the Bendex Chin Turret. This turret had originally been used on the YB-40 gunship project. While this experiment proved unsuccessful, the chin turret was found to be a major improvement to the B-17's forward firepower. This turret was fitted to the last eighty-six B-17Fs to come off the Douglas assembly line starting with block B-17F-75-DL.
  5. ^ "B-17F-70-DL: 42-3483 to 42-3503 | Production-block | B-17 Bomber Flying Fortress – The Queen Of The Skies" (in German). Retrieved 6 November 2020.
  6. ^ "42-3492 / Paper Doll | B-17 Bomber Flying Fortress – The Queen Of The Skies" (in German). Retrieved 13 November 2020.
  7. ^ Drury, Bob; Clavin, Tom (September 2016). "Suicide Run: The Final Flight of Old 666". HistoryNet.com. World History Group. Retrieved 29 October 2019.

Bibliography

  • Bishop, Cliff T. Fortresses of the Big Triangle First. Elsenham, UK: East Anglia Books, 1986. ISBN 1-869987-00-4.
  • Freeman, Roger A. The Mighty Eighth War Diary. St. Paul, Minnesota: Motorbooks International, 1990. ISBN 0-87938-495-6.
  • Freeman, Roger A. The Mighty Eighth War Manual. St. Paul, Minnesota: Motorbooks International, 1991. ISBN 0-87938-513-8.
  • Galland, Adolf. The First and the Last: Germany's Fighter Force in WWII (Fortunes of War). South Miami, Florida: Cerberus Press, 2005. ISBN 1-84145-020-0.
  • Levine, Alan J. The Strategic Bombing of Germany, 1940–1945. Westport, Connecticut: Praeger, 1992. ISBN 0-275-94319-4.