Want Wikipedia to look like this?   
Click here to upgrade your Wikipedia experience
Boeing YB-40 Flying Fortress | QuickiWiki

Boeing YB-40 Flying Fortress



Boeing XB-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
Manufacturer Lockheed-Vega
First flight September 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

Boeing-Lockheed Vega B-40 - Boeing YB-40 Flying Fortress
Boeing-Lockheed Vega B-40

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" for 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. - 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 with 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 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 - Boeing YB-40 Flying Fortress
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 gunned escort capable of accompanying bombers all the way to the target and back. Of the initial order of 13, one (43-5732) was lost on the delivery flight from Iceland to UK in May 1943; it force-landed in a peat bog on an offshore 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:

  • 29 May 1943 - attacked submarine pens and locks at Saint-Nazaire. Smaller strikes were made at Rennes naval depot and U-boat yards at La Pallice. In the attack, seven YB-40s were dispatched to Saint-Nazaire; they were unable to keep up with B-17s on their return from the target and modification of the waist and tail gun feeds and ammunition supplies was found to be needed. The YB-40s were sent to Technical Service Command at the Abbots Ripton 2nd Strategic Air Depot for modifications.
  • 15 June 1943 - four YB-40s were dispatched from Alconbury in a raid on Le Mans after completion of additional modifications.
  • 22 June 1943 - attack on the I.G. Farben Industrie Chemische Werke synthetic rubber plant at Hüls. The plant, representing a large percentage of the Germany's synthetic rubber producing capacity, was severely damaged. In the raid, 11 YB-40s were dispatched; aircraft 42-5735 was lost, being first damaged by flak and later shot down by Uffz. Bernhard Kunze in a Focke-Wulf Fw 190A-2 of JG 1 over Pont, Germany. The 10 crew members survived and were taken prisoner.
  • 25 June 1943 - attack on Blohm & Voss sub shops at Oldenburg. This was the secondary target, as the primary at Hamburg was obscured by clouds. In this raid, seven YB-40s were dispatched, of which two aborted. Two German aircraft were claimed as destroyed.
  • 26 June 1943 - scheduled but aborted participation in attack on the Luftwaffe air depot at Villacoublay, France (primary target) and also the Luftwaffe airfield at Poissy, France. The five YB-40s assigned to the attack were unable to form up with the bombing squadron, and returned to base.
  • 28 June 1943 - attack on the U-boat pens at Saint-Nazaire. In the raid, the only serviceable lock entrance to the pens was destroyed. In this attack, six YB-40s were dispatched, and one German aircraft was claimed as destroyed.
  • 29 June 1943 - scheduled participation in attack on the Luftwaffe air depot at Villacoublay, but aircraft returned to Alconbury due to clouds obscuring the target. In the raid, two YB-40s dispatched, one aborted.
  • 4 July 1943 - attacks on aircraft factories at Nantes and Le Mans, France. In these raids, two YB-40s were dispatched to Nantes and one to Le Mans.
  • 10 July 1943 - attack on Caen/Carpiquet airfield. In this raid, five YB-40s were dispatched.
  • 14 July 1943 - attacked Luftwaffe air depot at Villacoublay. In this raid, five YB-40s were dispatched.
  • 17 July 1943 - YB-40s recalled from a raid on Hannover due to bad weather. In this raid, two YB-40s were dispatched.
  • 24 July 1943 - YB-40s recalled from an attack on Bergen, Norway due to cloud cover. In this raid, one YB-40 was dispatched.
  • 28 July 1943 - attack on the Fieseler aircraft factory at Kassel. In this raid, two YB-40s were dispatched.
  • 29 July 1943 - attack on U-boat yards at Kiel. In this raid, two YB-40s were dispatched.


Boeing YB-40 Flying Fortress, 42-5736 (&quotTampa 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
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 German fighter kills and two probables (likely kills) were claimed, and one YB-40 was lost, shot down on the 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.

Overall the concept proved a failure because the YB-40 could not keep up with standard B-17Fs, particularly after they had dropped their bombs.[3][N 1] Despite the failure of the project as an operational aircraft, it led directly to the Bendix chin turret's fitment on the last 86 Douglas-built B-17F-75-DL production block aircraft,[5] and were part of the standardized modifications conspicuous on the final production variant of the B-17, the B-17G:

  • Chin turret (first introduced on the last 86 Douglas-built "final production" blocks of the B-17F-DL aircraft)
  • Offset waist gun positions
  • Improved tail gunner station with much larger windows, usually nicknamed the "Cheyenne", after the Cheyenne modification center.

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.


 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)

General characteristics



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



  1. ^ Adolf Galland (commander of the Luftwaffe fighter force) thought the YB-40`s successes were "insignificant".[4]


  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. ^ Galland 2005, p. 183.
  5. ^ Lyman, Troy (May 12, 2003). "B17 — Queen of the Sky — The B-17F". http://www.b17queenofthesky.com/. Troy Lyman's B-17 Flying Fortress Site. Retrieved June 24, 2014. 


Fortresses of the Big Triangle First - a History of the Aircraft Assigned to the First Wing and First Bombardment Division of the Eighth Air Force from August 1942 to 31st March 1944
Cliff T. Bishop (1986)
Fortresses of the Big Triangle First - a History of the Aircraft Assigned to the First Wing and First Bombardment Division of the Eighth Air Force from August 1942 to 31st March 1944
The Mighty Eighth War Diary
Roger Anthony Freeman:::Alan Crouchman:::Vic Maslen (1990)
The US 8th Air Force - it did not become known as the "Mighty Eighth" until these books were published and the name stuck - was based in England in the second half of World War II, from where it flew fighter and bomber missions over Europe. In addition to a veteran support back home, the Eighth and its aircraft have been avidly studied in the postwar years. This work chronicles each action which the units flew, the aircraft which took part and the results. Information has been updated for this edition. This volume is the second part of the re-issued "Mighty Eighth" trilogy.
Mighty Eighth War Manual
Roger Anthony Freeman (1991)
The Mighty Eighth was the largest striking force ever committed to battle, and putting it in the air remains one of the greatest military achievements of the Second World War. Over 1,700 aircraft, involving 15,000 men and a vastly sophisticated supply chain, engaged in a ceaseless war of high-altitude daylight precision bombing. More than 300 photographs, maps, and line drawings--along with details of the procedures and improvisations that went into play--tell the history of this incredible success. A leading authority on WWII aircraft and their pilots (the author of six books on this division alone) discloses the operational techniques of bombers and fighters; the background behind weather and photographic reconnaissance; the secrets of special operations; as well as experimentation, training, logistics, and more. All the installations, armament, and equipment are here, too, from the airfields and depots to the gunsights and communication sets to the flight clothing and oxygen tanks. A splendid tribute to the men who helped safeguard liberty.
The Strategic Bombing of Germany, 1940-1945
Alan Levine (1992)
This book is the only full-scale account of the strategic air offensive against Germany published in the last twenty years, and is the only one that treats the British and the Americans with parity. Much of what Levine writes about British operations will be unfamiliar to American readers. He has stressed the importance of winning air superiority and the role of escort fighters in strategic bombing, and has given more attention to the German side than most writers on air warfare have. Levine gets past a simple account of what we did to them and describes the target systems and German countermeasures in detail, providing exact yet dramatic accounts of the great bomber operations--the Ruhr dams, Ploesti, and Regensburg and Schweinfurt. The book is broad-guaged, touching many matters, from the development of bombing doctrine before the war to the technical development of the Luftwaffe and the RAF, jets and V-weapons, to the role of the heavy bombers in supporting land and sea operations.Levine stresses the impact of bombing on the war, and generally endorses the strategic air campaign as worthwhile and effective. But he concludes that many mistakes were made by the Allies--both the British and the Americans--in tactics, the development of equipment, and in the selection of targets. Levine sees strategic bombing as a powerful tool that was often misused, particularly when the doctrine of area bombing flourished. Scholars, students, and buffs interested in World War II and/or the history of aviation will find this study of great interest.
  • 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.
This page is based on data from Wikipedia (read/edit), Freebase, Amazon and YouTube under respective licenses.
Text is released under the Creative Commons Attribution-ShareAlike License.