B-17 Flying Fortress variants
The following is an extensive catalogue of the variants and specific unique elements of each variant and/or design stage of the Boeing B-17 Flying Fortress heavy bomber. For a broader article on the history of the B-17, see B-17 Flying Fortress.
Boeing Model 299
The Boeing 299 was the original bomber design made by Boeing to fulfill a request by the United States Army Air Corps for a bomber capable of carrying 2,000 lb of bombs 2,000 miles at 200 mph. In 1935, the Boeing 299 competed with several entries by other companies at an evaluation at Wright Field.
On its flight from Seattle to Wright Field for the competition, the 299 set a nonstop speed record of 252 mph. Though it crashed during the demonstration, the crash was due to pilot error, not any flaw in the airplane. Despite the crash (and more importantly, its much higher cost per unit), Air Corps leaders were impressed by the 299. Boeing was awarded with a development contract.
- Archived newspaper article (USAF Museum)
- Encyclopedia of American Aircraft
- Model 299 Crash (USAF Museum)
- Specifications (USAF Museum)
Though still enthusiastic about the design, the Army Air Corps decided to cut the order for service test YB-17s from 65 to 13 after the original 299 crashed. On 1936 November 20, they changed the source of funding from normal funding to 'F-1' procurement, and redesignated the plan Y1B-17 before it even flew.
Unlike its predecessor, which had used Pratt & Whitney 'Wasp' radials, the Y1B-17 used the Wright 'Cyclone' that would become standard on the B-17. Several changes were made in the armament, and the crew was reduced from seven to six. Most changes were minor: the most notable was switching from double-arm to single-arm landing gear.
On 1936 December 7, five days after the first flight of the Y1B-17, the brakes of the aircraft fused during landing, and it nosed over. Though damage was minimal, the cumulative impact of this event and the crash of the 299 triggered a Congressional investigation. After the crash the Army Air Corps was on its toes; another crash would mean the end of the programme.
Though they were meant for testing, the commander of Army General Head Quarters (Air Force), Major General Frank Andrews, decided to assign twelve Y1B-17s to the Second Bomb Group at Langley Field, Virginia. Andrews reasoned that it was best to develop heavy bombing techniques as quickly as possible. Of the thirteen, only one was used for flight testing.
In 1937, the twelve Y1B-17s with the 2nd Bombardment Group at Langley Field represented the entire American fleet of Heavy Bombers. Most of the time they spent with the planes entailed eliminating problems with the aircraft. The most important development they made was the use of a checklist, to be reviewed by the pilot and copilot before takeoff. It was hoped that this system would prevent accidents similar to that that led to the loss of the 299.
In 1938 May, the Y1B-17s (now redesignated B-17) of the 2nd Bombardment Group took part in a demonstration in which they 'intercepted' the Italian liner Rex. Coming into contact with the liner while it was still 700 miles out at sea, the demonstration was meant to prove the range and navigational superiority of the B-17. It also showed that the bomber would be an effective tool for attacking an invasion force before reaching the United States. The Navy was furious about Army intrusion into their mission, and forced the War Department to issue an order restricting the Army Air Force from operations more than a hundred miles from the American coast.
After three years of flight, no serious incidents occurred with the B-17s. In 1940 October, they were transferred to the 19th Bombardment Group at March Field.
The aircraft that became the sole Y1B-17A was originally ordered as a static test bed. However, when one of the Y1B-17s survived an inadvertent violent spin during a flight in a thunderhead, Air Corps leaders decided that the plane was exceptionally robust and that there would be no need for static testing. Instead, it was used as a testbed for engine types. After studying a variety of configurations, use of a bottom-mounted turbo-supercharger was settled on. This turbo-supercharge became standard on the first production model, and allowed it to fly higher and faster than the Y1B-17. When testing was complete the Y1B-17A was renamed the B-17A.
The B-17B (299M) was the first production model of the B-17, and was essentially a B-17A with a larger rudder, larger flaps, and a redesigned nose and 1200-hp R-1820-51 engines. The gun turret in the upper nose was replaced with a flexible .30-calibre machine gun at its extreme tip, and the bomb-aiming window was replaced with an optical flat in the lower part of the nose fairing.
In the interior of the plane, crew members were rearranged. Many internal systems were revised. Most notable of these was a switch from pneumatic to hydraulic brakes.
In October 1942 all planes of the B-17B designation were redesignated RB-17B, R- indicating 'restricted'. The RB-17B was used for training, transport, messenger, and liaison duties. It was in effect a designation of obsolescence.
The "B" series made it's maiden flight on June 27 1939. 39 were built in a single production run, but Army Air Corps serial numbers were scattered over several batches. This was because of limited funding: the Army Air Corps could only buy a few B-17Bs at a time.
The B-17C was a B-17B with a number of improvements, including more powerful R-1820-65 engines. To boost crew safety, the waist-mounted gun blisters were replaced with teardrop-shaped sliding panels flush with the fuselage, and the ventral gun blister by a metal housing dubbed a 'bathtub turret'. Some of the most important additions were self-sealing fuel tanks and defensive armor.
With the passage of the Lend-lease Act in 1941, the Royal Air Force began clamoring for use of the B-17. At that time, the Army Air Corps was suffering from shortages of the B-17, but hesitantly agreed to provide twenty planes to the RAF. Though the Army Air Corps did not consider the B-17C ready for combat, it was desperately needed in Britain. The twenty planes were placed immediately into frontline service as the Fortress Mk I.
In Britain, the plane performed unremarkably. By 1941 September, 22 attacks had been flown using a total of 39 planes. Eight of the twenty were destroyed by the end of the war, largely because their guns tended to freeze at high altitude and were generally unable to effectively protect the Fortresses. Their success as a bomber was also limited, largely because they were unable to hit anything from the altitudes at which they flew.
The first "C" series flew in July 1940, 38 were built. The eighteen remaining after twenty were transferred to the RAF were modified to the configuration used in the B-17D. However, one of these, B-17C 40-2047, crashed while being ferried from Salt Lake City, UT, to McClellan Field, CA, on November 2, 1941. 
- Encyclopedia of American Aircraft (B-17C)
- Encyclopedia of American Aircraft (Fortress I)
- USAF Museum
Though changes in the design made the Army Air Corps decide that the B-17D was worthy of a new subdesignation, the B-17C and B-17D were very similar. In fact, both were given the same subdesignation (299H) by Boeing. Several minor changes were made, both internally and externally. Outside, the engines received a set of cowling flaps for better cooling, and the external bomb racks were removed. On the inside, the electrical system was revised, and another crew member added. In the dorsal turret and bathtub turret, the guns were doubled, bringing the total armament to one 0.30-inch and six 0.50-inch machine guns. The B-17D also featured more extensive armor protection. A total of 42 were built, and the 18 remaining B-17Cs were also converted to B-17D format. The sole surviving example of this model of the Flying Fortress exists at the National Air and Space Museum in Washington D.C., and is known as "The Swoose"...former crew member Frank Kurtz named his daughter Swoosie Kurtz after this aircraft.
- Encyclopedia of American Aircraft
- USAF Museum
-  on the B-17D "The Swoose".
The B-17E (299-O) was an extensive redesign of that used in previous models up to the B-17D. The most obvious change was that in the vertical stabiliser, resulting in a shape that was distinctive for the time. (Compare these images of the B-17D and B-17E.)
Because experience had shown that the plane would be vulnerable to attack from behind, a tail gunner and powered two gun turret behind the cockpit were added to the B-17E design. (Before this, crews had to devise elaborate maneuvers, to deal with a direct attack from behind, including jerking the aircraft laterally, allowing the waist gunners to alternate shots at it.) The configuration with 3-window box would also appear on the B-29, and also adopted by Soviet bombers as late as the Tupolev Tu-16 Badger, and in different form on the B-52. The teardrop-shaped sliding panels of the waist gunners were replaced by larger rectangular windows for better visibility. Extensive redesign of B-17. Tail improved. Tail gunner added as per combat necessity. Sliding panels used by waist-gunners changed to a rectangular shape. In the initial fifth of the production run, the ventral bathtub turret was replaced by a remote-sighted Bendix turret. Aircraft built after that used a Sperry ball turret.
A total of 512 were built, making the B-17E the first mass-produced version of the B-17. One of these was later converted to the XB-38 Flying Fortress. Since production this size was too large for Boeing alone to handle, they were assisted by the Vega division of Lockheed and Douglas. Boeing also built a new plant, and Douglas added one specifically for production of the B-17.
In the middle of 1942, 45 B-17Es were transferred to the RAF, where they served under the designation Fortress IIA. Likely because of the shortcomings of the Fortress I (B-17C), the RAF decided not to use the Fortress IIA as a daylight high-altitude bomber, the role for which it had been designed. Rather, they were transferred to the Coastal Command for anti-submarine patrol.
- Encyclopedia of American Aircraft (B-17E)
- Encyclopedia of American Aircraft (Fortress IIA)
- USAF Museum
The B-17F was an upgrade of the B-17E, although outwardly the types were distinguished only by exchanging the framed nose-glass for a molded one-piece plexiglas cone. Late production "F" series received a cheek-mounted gun either side of the nose, and fully-feathering paddle bladed propellers. Numerous internal changes were made to improve the effectiveness, range, and load capacity of the B-17. However once placed in combat service, it was found to be tail heavy. The weight of gunners and ammunition when combat-loaded moved the center of gravity rearward from its design point and forced the constant use of elevator trim tab, stressing this component. In combat the B-17F proved almost immediately to have inadequate defensive protection when attacked from the front. Various armament configurations were tested in the field, but the problem was not adequately addressed until the production of the B-17G.
By using a stronger undercarriage, the maximum bomb capacity was increased from 4,200 lb to 8,000 lb. Though this modification reduced cruise speed by 70 mph (100 km/h), the increase in bomb capacity was a decided advantage. A number of other modifications were made, including re-integrating external bomb racks, but because of its negative impact on both rate-of-climb and high altitude flight the configuration was rarely used and the racks were removed.
Range and combat radius were extended with the installation in mid-production of additional fuel cells in the wings. Called "Tokyo tanks", nine self-sealing rubber-composition tanks were mounted inside each wing on either side of the joint between the inner and outer wing sections. Totaling 1,080 additional gallons to the 1,700 available on the first B-17Fs, the Tokyo tanks added approximately 900 miles to the bomber's range.
3405 were built: 2300 by Boeing, 605 by Douglas, and 500 by Lockheed (Vega). These included the famous Memphis Belle. Nineteen were transferred to the RAF, where they served with RAF Coastal Command as the Fortress II.
- Freeman, Roger. The Mighty Eighth War Manual (1991) pp. 148-153. ISBN 0-87938-513-8
- Bishop, Cliff T. Fortresses of the Big Triangle First (1986) p. 51, ISBN 1-869987-00-4
Generally considered the defining B-17 design, all changes made in the B-17F production run were incorporated into the final version. It also included a Bendix chin-turret, an innovation derived from the unsuccessful YB-40 escort version, bringing defensive armament to thirteen .50-calibre machine guns. Some 8,680 were built, and dozens were converted for several different uses:
- CB-17G. Troop transport version, capable of carrying 64 troops.
- DB-17G. Drone variant.
- JB-17G. Engine test-bed.
- QB-17L. Target drone.
- QB-17N Target drone.
- RB-17G. Reconnaissance variant.
- SB-17G. Rescue version, originally designated B-17H. Featured A-1 lifeboat under fuselage. After World War II, armament on the SB-17Gs was removed; it was reinstated when the Korean conflict began.
- TB-17G. Special duty training version.
- VB-17G. VIP transport.
- PB-1. This designation was given to one B-17F and one B-17G. They were used by the US Navy for various test projects.
- PB-1G. This designation was given to 17 B-17Gs used by US Coast Guard as air-sea rescue aircraft.
- PB-1W. This designation was given to 31 B-17Gs used by the US Navy as the first airborne early warning aircraft/ AWACS.
Eighty-five B-17Gs were transferred to the Royal Air Force, where they were used as the Fortress III. They operated with two squadrons of Bomber Command's No. 100 Group RAF at RAF Sculthorpe, where they were used for electronic countermeasures missions to confuse and jam enemy radar. They were also used as decoys during night bombing attacks. They took part in various such operations until they were disbanded in 1945 July.
The XB-38 was a modification project undertaken primarily by the Vega division of Lockheed on the ninth B-17E built. Its primary purpose was testing the feasibility of liquid-cooled Allison V-1710-89 engines. It was meant as an improved version of the B-17, and a variant that could be used if the Wright R-1820 engine became scarce. Completing the modifications took less than a year, and the XB-38 made its first flight on 1943 May 19. While it showed a slightly higher top speed, after a few flights it had to be grounded due to a problem with engine manifold joints leaking exhaust. Following the fixing of this problem, testing continued until the ninth flight on 1943 June 16. During this flight, the third (right inboard) engine caught fire, and the crew was forced to bail out. The XB-38 was destroyed and the project cancelled. The gains in modification were minimal and would have been disruptive to production of existing models.
Prior to the introduction of the P-51 Mustang, a B-17 escort variant called the YB-40 was introduced. This aircraft differed from the standard B-17 in that a second dorsal turret was installed between the top turret and the waist guns; and the single 0.50-calibre (12.7 mm) machine gun at each waist station was replaced by a pair of 0.5-calibre (12.7 mm) guns. In addition, the bombardier’s equipment was replaced with two 0.50-calibre (12.7 mm) machine guns in a ‘chin’ turret to augment the existing ‘cheek’ machine guns, and the bomb bay itself was converted to a magazine. The YB-40 would provide a heavily-gunned escort capable of accompanying the bombers all the way to the target and back. The aircraft was deemed a failure because it could not keep up with standard B-17Fs once they had dropped bombs. It was withdrawn from service after fourteen missions. (26 built: 1 XB-40 prototype, 21 YB-40 pre-production aircraft, 4 TB-40 training aircraft.)
C-108 Flying Fortress
Four B-17s were converted to serve as cargo carriers and V.I.P. transports under the designation C-108 Flying Fortress. (Many more served in the same roles under the designations CB-17 and VB-17, respectively.) The first of them, designated XC-108 was a B-17E partially stripped of military equipment and outfitted with various living accommodations. It served as a V.I.P. transport for General Douglas MacArthur. A similar conversion was made on a B-17F, which was redesignated YC-108. The third plane, designated XC-108A, was made to test the feasibility of converting obsolete bombers to cargo aircraft. Based in India, it ferried supplies over the Himalaya to the base for the B-29 Superfortress in Chengdu, China. It proved a difficult plane, and was sent back to the United States to be scrapped. The final one was built under the designation XC-108B, and was used as a tanker to transport fuel from India to Chengdu.
F-9 Flying Fortress
Several B-17s were converted to long-range photographic reconnaissance aircraft, designated F-9 Flying Fortress. (The F- here stands for 'fotorecon' and must not be confused with F- for 'fighter', which was not introduced until after the war.)
The first F-9 aircraft were sixteen B-17Fs, with bombing equipment replaced by photographic equipment. Some of the defensive armament was kept. An uncertain number more were converted to a similar configuration to the F-9, but differed in minor details of their cameras, and received the designation F-9A. Some of these, along with more B-17Fs, received further camera alterations and became the F-9B. The last variants was the F-9C, which was given to ten B-17G, converted in a similar fashion to the previous plances. Those surviving in 1948 were at first redesignated later RB-17G (R indicating 'reconnaissance').
- FB-17. - Post-war redesignation of all F-9 photo-reconnaissance aircraft.
Late in World War II, at least 25 B-17s were fitted with radio controls to be used as drones designated BQ-7 missiles, constructed under the auspices of 'Operation Aphrodite'. Loaded with up to 20,000 lb (9,070kg) of Torpex high explosive and enough fuel for a range of 350 miles (563km) they were used to attack U-boat pens, V-1 missile sites, and other bomb-resistant fortifications.
The BQ-7s would be taken aloft by two volunteer crew members, who would take it up to 2,000 feet, point it toward the target, and transfer control to another B-17. They would then bail out through the open cockpit while still safely over England. The controlling B-17 would follow the BQ-7, and lock its controls into a collision course with its target, then turn around to escape.
Because remote-control hardware available at the time was insufficient for the task, Operation Aphrodite was riddled with problems. Between August 1944 and January 1945 15 BQ-7 were launched against Germany, none ever hit its target, and several crew were killed in various parachuting accidents. One bomber left a 100 foot crater in British soil and another circled an English city out of control. It was cancelled in early 1945.
PB-1 and PB-1W
The U.S. Navy received 48 B-17's towards the end of World War II, renamed PB-1. Post-war, the Navy acquired 31 B-17G's. Renamed PB-1W, these aircraft were fitted with AN/APS-20 radar and used to develop Airborne Early Warning eauipment and procedures. They were the precursors of today's Airborne Warning & Control (WACS) aircraft. These were later replace by Lockheed WV-2's.
- Encyclopedia of Aircraft of WWII
SB-17G and PB-1G
From 1945-1948 12 B-17G's were converted to B-17H's equipped with an airborne lifeboat and ASV radar for USAAF air-sea rescue duties. The US Coast Guard flew 17 similar aircraft as PB-1G's
- B-17 Flying Fortress
- Category:Lists of aircraft variants
- List of bomber aircraft
- List of military aircraft of the United States
- List of B-17 Flying Fortress serial numbers
- Lonesome Polecat II
- Hess, William N. Big Bombers of WWII. Ann Arbor, Michigan: Lowe & B. Hould, 1998. ISBN 0-681-07570-8.
- Jablonski, Edward. Flying Fortress. New York: Doubleday, 1965. ISBN 0-385-03855-0.
- Johnson, Frederick A. Boeing B-17 Flying Fortress (Warbird Tech Series, Volume 7). Stillwater, Minnesota: Voyageur Press, 2001. ISBN 1-58007-052-3.
- Lloyd, Alwyn T. B-17 Flying Fortress in Detail and Scale. Fallbrook, California: Aero Publishers, 1986. ISBN 0-8168-5029-1.
- O'Leary, Michael. Boeing B-17 Flying Fortress (Osprey Production Line to Frontline 2). Botley, Oxford, United Kingdom: Osprey Publishing, 1999. ISBN 1-85532-814-3.
- [14.html] accessed on 12 January, 2005.