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The Boeing YB-40 Flying Fortress was a modification for operational testing purposes of the
B-17 Flying Fortress The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC). Relatively fast and high-flying for a bomber of its era, the B-17 was used primarily in the European Theater ...
bomber A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped from an air ...
aircraft, converted to act as a heavily armed
gunship A gunship is a military aircraft armed with heavy aircraft guns, primarily intended for attacking ground targets either as airstrike or as close air support. In modern usage the term "gunship" refers to fixed-wing aircraft having laterally-m ...
to support other bombers during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. At the time of its development, long-range
fighter aircraft Fighter aircraft are fixed-wing military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield ...
such as the
North American P-51 Mustang The North American Aviation P-51 Mustang is an American long-range, single-seat fighter and fighter-bomber used during World War II and the Korean War, among other conflicts. The Mustang was designed in April 1940 by a team headed by James ...
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

Work on the
prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and software programming. A prototype is generally used to ...
, 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 Browning machine guns are a family of machine gun designs by John Browning, a prolific weapon designer. These include: *M1895 Colt–Browning machine gun, based on a design dating to 1889, was the first successful gas-operated machine gun to ent ...
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.Bishop 1986, pp. 69, 73, 246–247. 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
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. Additional
armor plating Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, shells, rockets, and missiles, protecting the personnel inside from enemy fire. Such vehicles include armoured fighti ...
was installed to protect crew positions. The aircraft's gross weight was some 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 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 In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding ...
of the gun stations.Freeman 1991, pp. 154–155. 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 The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated as ...
at their
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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. 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. 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.


Operational history

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 Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
to the UK in May 1943; it force-landed in a
peat bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...
on a Scottish island after running out of fuel. Although removed to
Stornoway Stornoway (; gd, Steòrnabhagh; sco, Stornowa) is the main town of the Western Isles and the capital of Lewis and Harris in Scotland. The town's population is around 6,953, making it by far the largest town in the Outer Hebrides, as well ...
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 Royal Air Force Alconbury or more simply RAF Alconbury is an active Royal Air Force station near Huntingdon, England. The airfield is in the civil parish of The Stukeleys, close to the villages of Great Stukeley, Little Stukeley, and Alconbur ...
(AAF-102) on 8 May 1943. YB-40s flew in the following operational missions: *29 May 1943 – attacked
submarine pen A submarine pen (''U-Boot-Bunker'' in German) is a type of submarine base that acts as a bunker to protect submarines from air attack. The term is generally applied to submarine bases constructed during World War II, particularly in Germany and ...
s and locks at
Saint-Nazaire Saint-Nazaire (; ; Gallo: ''Saint-Nazère/Saint-Nazaer'') is a commune in the Loire-Atlantique department in western France, in traditional Brittany. The town has a major harbour on the right bank of the Loire estuary, near the Atlantic Ocea ...
. Smaller strikes were made at
Rennes Rennes (; br, Roazhon ; Gallo: ''Resnn''; ) is a city in the east of Brittany in northwestern France at the confluence of the Ille and the Vilaine. Rennes is the prefecture of the region of Brittany, as well as the Ille-et-Vilaine departme ...
naval depot and
U-boat U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare ro ...
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 Abbots Ripton is a village and civil parish in Cambridgeshire, England. Abbots Ripton is situated within Huntingdonshire which is a non-metropolitan district of Cambridgeshire as well as being an historic county of England. Abbots Ripton lies ap ...
2nd Strategic Air Depot for modifications. *15 June 1943 – four YB-40s were dispatched from Alconbury in a raid on
Le Mans Le Mans (, ) is a city in northwestern France on the Sarthe River where it meets the Huisne. Traditionally the capital of the province of Maine, it is now the capital of the Sarthe department and the seat of the Roman Catholic diocese of Le ...
after completion of additional modifications. *22 June 1943 – attack on the
I.G. Farben Interessengemeinschaft Farbenindustrie AG (), commonly known as IG Farben (German for 'IG Dyestuffs'), was a German chemical and pharmaceutical conglomerate. Formed in 1925 from a merger of six chemical companies—BASF, Bayer, Hoechst, Agfa, ...
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 Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based ...
and later shot down by a
Focke-Wulf Fw 190 The Focke-Wulf Fw 190, nicknamed ''Würger'' (" Shrike") is a German single-seat, single-engine fighter aircraft designed by Kurt Tank at Focke-Wulf in the late 1930s and widely used during World War II. Along with its well-known counterpart, ...
A-2 of JG 1 over Pont, Germany. The 10 crew members survived and were taken prisoner. *25 June 1943 – attack on
Blohm & Voss Blohm+Voss (B+V), also written historically as Blohm & Voss, Blohm und Voß etc., is a German shipbuilding and engineering company. Founded in Hamburg in 1877 to specialise in steel-hulled ships, its most famous product was the World War II battl ...
U-boat machine shops at Oldenburg. This was the secondary target, as the primary at
Hamburg Hamburg (, ; nds, label=Hamburg German, Low Saxon, Hamborg ), officially the Free and Hanseatic City of Hamburg (german: Freie und Hansestadt Hamburg; nds, label=Low Saxon, Friee un Hansestadt Hamborg),. is the List of cities in Germany by popul ...
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 Poissy () is a commune in the Yvelines department in the Île-de-France region in north-central France. It is located in the western suburbs of Paris, from the centre of Paris. Inhabitants are called ''Pisciacais'' in French. Poissy is one ...
, 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 Nantes (, , ; Gallo: or ; ) is a city in Loire-Atlantique on the Loire, from the Atlantic coast. The city is the sixth largest in France, with a population of 314,138 in Nantes proper and a metropolitan area of nearly 1 million inhabita ...
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 Caen (, ; nrf, Kaem) is a commune in northwestern France. It is the prefecture of the department of Calvados. The city proper has 105,512 inhabitants (), while its functional urban area has 470,000,Carpiquet Carpiquet () is a commune in the Calvados department in the Normandy region in northwestern France. Caen – Carpiquet Airport is located in Carpiquet. Geography Carpiquet is on the western side of the Caen metropolitan area. The town is div ...
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 Hanover (; german: Hannover ; nds, Hannober) is the capital and largest city of the German state of Lower Saxony. Its 535,932 (2021) inhabitants make it the 13th-largest city in Germany as well as the fourth-largest city in Northern Germany ...
due to bad weather. In this raid, two YB-40s were dispatched. *24 July 1943 – YB-40s recalled from an attack on
Bergen Bergen (), historically Bjørgvin, is a city and municipalities of Norway, municipality in Vestland county on the Western Norway, west coast of Norway. , its population is roughly 285,900. Bergen is the list of towns and cities in Norway, secon ...
,
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...
due to cloud cover. In this raid, one YB-40 was dispatched. *28 July 1943 – attack on the Fieseler aircraft factory at
Kassel Kassel (; in Germany, spelled Cassel until 1926) is a city on the Fulda River in northern Hesse, Germany. It is the administrative seat of the Regierungsbezirk Kassel and the district of the same name and had 201,048 inhabitants in December 2020 ...
. In this raid, two YB-40s were dispatched. *29 July 1943 – attack on U-boat yards at
Kiel Kiel () is the capital and most populous city in the northern German state of Schleswig-Holstein, with a population of 246,243 (2021). Kiel lies approximately north of Hamburg. Due to its geographic location in the southeast of the Jutland ...
. In this raid, two YB-40s were dispatched.


Summary

Altogether of the 59 aircraft dispatched, 48
sortie A sortie (from the French word meaning ''exit'' or from Latin root ''surgere'' meaning to "rise up") is a deployment or dispatch of one military unit, be it an aircraft An aircraft is a vehicle that is able to flight, fly by gaining supp ...
s 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 Adolf Josef Ferdinand Galland (19 March 1912 – 9 February 1996) was a German Luftwaffe general and flying ace who served throughout the Second World War in Europe. He flew 705 combat missions, and fought on the Western Front and in the Defenc ...
considered the gunship's handful of combat victories to be "insignificant" and not worth the cost of the aircraft.Levine 1992, p. 90. 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) Douglas-built aircraft starting with the B-17F-70-DL production block, 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 RAF Kimbolton is a former Royal Air Force station located west of Huntingdon, Cambridgeshire, England. History USAAF use The airfield was originally built in 1941 for RAF Bomber Command, then expanded to Class A airfield standards for use b ...
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 ''The Best Years of Our Lives'' (also known as ''Glory for Me'' and ''Home Again'') is a 1946 American epic drama film directed by William Wyler, and starring Myrna Loy, Fredric March, Dana Andrews, Teresa Wright, Virginia Mayo and Harold Rus ...
'', in the famous scene shot at the Ontario "graveyard". No airframes were sold on the civil market.


Operators

; *
United States Army Air Forces The United States Army Air Forces (USAAF or AAF) was the major land-based aerial warfare service component of the United States Army and ''de facto'' aerial warfare service branch of the United States during and immediately after World War II ...
: XB-40: Conversion of B-17F-1-BO 41-24342 (Not deployed to
ETO ETO may refer to: Science and technology * Emitter turn off thyristor, a semiconductor device * Ethylene oxide, an organic compound * RUNX1T1, a gene * Efforts to Outcomes, software produced by Social Solutions Sports * ETO-SZESE Győr FKC, a ...
) : 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)


See also


References


Notes


Citations


Bibliography

* Bishop, Cliff T. ''Fortresses of the Big Triangle First.'' Elsenham, UK: East Anglia Books, 1986. . * Freeman, Roger A. ''The Mighty Eighth War Diary.'' St. Paul, Minnesota: Motorbooks International, 1990. . * Freeman, Roger A. ''The Mighty Eighth War Manual.'' St. Paul, Minnesota: Motorbooks International, 1991. . * Galland, Adolf. ''The First and the Last: Germany's Fighter Force in WWII'' (Fortunes of War). South Miami, Florida: Cerberus Press, 2005. . * Levine, Alan J. ''The Strategic Bombing of Germany, 1940–1945.'' Westport, Connecticut: Praeger, 1992. .


External links


YB-40 Gun Ship Completes a Successful Mission

USAF Factsheet, Boeing YB-40 Flying Fortress

The YB-40 gunship was both more and less than planners expected
{{USAF bomber aircraft B-40 Flying Fortress Boeing B-40 Flying Fortress 1940s United States fighter aircraft Four-engined tractor aircraft Low-wing aircraft B-40 Aircraft first flown in 1942 Four-engined piston aircraft