Boeing YB-40 Flying Fortress

Twelve YB-40s were assigned to the 92nd Bomb Group / 327th Bomb Squadron for combat trials where they flew missions from May through July 1943. This is 42-5743 “Woolaroc” and 42-5741 “Chicago” which operated from RAF Alconbury. The port cheek guns have been fitted on both these aircraft.

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

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.

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.

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.

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.

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.

Serials from Freeman:

41-24341 XB-40 prototype

42-5732

42-5733 Peoria Prowler

42-5734 Seymore Angel, later renamed Red Balloon, Old Ironsides

42-5735 Wango Wango, lost on Hüls raid 22JUN43

42-5736 Tampa Tornado

42-5737 Dakota Demon

42-5738 Boston Tea Party

42-5739 Lufkin Ruffian

42-5740 Monticello

42-5741 Chicago, later renamed Guardian Angel

42-5742 Plain Dealing Express

42-5743 Woolaroc

42-5744 Dollie Madison

42-5871

42-5920

42-5921

42-5922

42-5923

42-5924

42-5925

42-5926

42-5927

42-5833 TB-40 crew trainer

42-5834 TB-40 crew trainer

42-5872 TB-40 crew trainer

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 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:

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 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 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 U-boat machine 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.

Summary

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. 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 (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), 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.

Factories were trying to find 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. 

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: United States Army Air Forces

XB-40: Conversion of B-17F-1-BO 41-24341 (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).

Details (YB-40)

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

Crew: 10

Length: 74 ft 9 in (22.6 m)

Wingspan: 103 ft 9 in (31.4 m)

Height: 19 ft 1 in (5.8 m)

Wing area: 1,527 sq ft (141.9 m2)

Empty weight: 54,900 lb (24,900 kg)

Gross weight: 63,500 lb (28,800 kg)

Maximum takeoff weight: 74,000 lb (33,565 kg)

Powerplant: 4 × Wright R-1820-65 "Cyclone" turbosupercharged radial engines, 1,200 hp (895 kW) each

Maximum speed: 292 mph (470 km/h, 254 kn)

Cruise speed: 196 mph (315 km/h, 170 kn)

Range: 2,260 mi (3,640 km, 1,960 nmi)

Service ceiling: 29,200 ft (8,900 m)

Rate of climb: 416 ft/min (2.11 m/s)

Wing loading: 47.2 lb/sq ft (231 kg/m2)

Power/mass: 0.066 hp/lb (0.11 kW/kg)

Armament: 18 (or more) × .50 in (12.7 mm) M2 Browning machine guns. Typically used 14–16, with room for up to 30

Ammunition Carried

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

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.

Boeing-Lockeed Vega XB-40. The prototype XB-40 was modified by Lockheed Vega (Project V-139) by converting the second production B-17F-1-BO (41-24341), 10 November 1942. (USAF)

A well-known photograph showing the increased firepower of the YB-40 with eight of the fourteen .50 caliber machine guns visible. Several different armament configurations were proposed, including 40 mm or 20 mm cannon, and reportedly one with a total of thirty .50 caliber guns.

Close-up of the array of 50-cal guns on the Boeing YB-40 Flying Fortress, 1943. (USAAF)

A nice external view of the port waist gun position showing the twin .50 calibers mounted there. Note the wind deflector forward of the opening and that the twin guns are mounted at the center of the window, not more forward as was standard for the single-gun installation.

A view from inside the YB-40 looking forward, showing the improved dual waist gun installation. The YB-40 introduced the staggered waist gun layout to the Flying Fortress design, this picture shows a modification to improve the ammunition feed to the guns. Note the large quantity of ammunition carried for these guns and the effort to shift the weight forward.

Emblem of the 327th Bombardment Squadron, featuring characters (Alley Oop and Dinny) from the Alley Oop comic strip, 1943. (USAAF) The 327th flew the YB-40 gunships.

Boeing YB-40 Flying Fortress, 42-5736 ("Tampa Tornado") on display at RAF Kimbolton, England, Oct 2, 1943 when it was shown to attendees at a party for local children. The subdued national insignia is apparent, Neutral Gray was substituted for the more usual Insignia White. (USAAF)

The Tampa Tornado again with two sister ships at Alconbury. The YB-40 experiment was not deemed a success. While firepower was improved it was still not sufficient to deter the Jagdwaffe. The YB-40 contributed nothing to the total bombs on target, and the weight of the additional guns and ammunition made it difficult for the YB-40s to keep up with a B-17 formation, especially after they had released their bomb loads.

The YB-40s were withdrawn from the European Theater and redesignated as TB-40s where they served Stateside in the gunnery training role. Here is 42-5925 along with four Bell P-63 King Cobras on a training flight.

YB-40 in flight.

A major innovation was the installation a Bendix remote turret under the Bombardier’s position to improve forward firepower. Both German and Japanese pilots quickly discovered the relative weakness of frontal firepower of the Flying Fortress and concentrated their attacks from the nose whenever possible. This installation proved a success prompting Douglass to install Bendix chin turrets on the final eighty-six B-17Fs they produced, the Bendix turrets became standard at all three manufacturers with the B-17G model. This YB-40 does not yet carry cheek guns for the Navigator, although these would be added later.

Boeing YB-40 Flying Fortress, 41-24341.

Another photograph of the XB-40 prototype 41-24341. By this time the dorsal fairing has been abruptly truncated which increased drag but improved the fields of fire for the second turret. This would become the standard for the subsequent YB-40 series. If you look closely you can see some artwork on the fuselage side.

Boeing XB-40 Flying Fortress (41-24341). The Boeing YB-40 Escort Bomber or “Bomber-Fighter” was a B-17 with additional defensive armament, armor, and ammunition built in an attempt to provide defense for B-17 formations over Europe. This is the prototype XB-40, converted from the second production B-17F-1-BO serial number 41-24341 by Lockheed-Vega. Note the second dorsal turret mounted in the radio room and how the upper fairing extends to the turret.

The XB-40 was distinguished by the cockpit fairing extending to the second dorsal turret and a small blister at the waist window.

Boeing YB-40 Flying Fortress, 327th Bomb Squadron, 92nd Bomb Group, RAF Alconbury, UK, mid-1943.

Artwork on the fuselage side of a Boeing YB-40 Flying Fortress. Mickey Mouse is saying, “Let them come gang. I’ll take care of them!” Mickey Mouse was a popular subject for aircraft artwork, and not just among American aircrews. Notice how the bars and red surround added to the national insignia have been applied over the artwork.

View of pilot’s station on the Boeing XB-40 Flying Fortress.

View of co-pilot’s station on the Boeing XB-40 Flying Fortress.

A total of twenty-five B-17F were modified to YB-40 or TB-40 (gunnery trainer) standard. Here is a photograph of 42-5732 through 42-5745 which were delivered to the modification center at Tulsa in October and November of 1942 receiving their modifications. The work to install the powered turret in the radio compartment is underway.

Here is 42-5741 Chicago again, likely at RFC Ontario at the end of her service life. Note the lack of armament and the large training “buzz number”. Upon her return to the States she was renamed “Guardian Angel”. All of the YB-40s were scrapped after the war, none survive today. In the final assessment the YB-40 program contributed improvements to the defensive armament of standard Flying Fortresses, primarily the staggered waist gun positions and the Bendix chin turret in the nose.

YB-40 armament diagram.