Boeing 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 ( XB - 17 ) . 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 ( 907 kg ) of bombs 2 , 000 mi ( 3 , 218 km ) at 200 mph ( 322 km / h ) . 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 ( 406 km / h ) . Though it crashed during the demonstration , the crash was due to pilot error , not any flaw in the airplane . Despite the crash ( and more important , its much higher cost per unit ) , Air Corps leaders were impressed by the 299 . Boeing was awarded with a development contract . The aircraft has been since been referred to as the XB - 17 but the designation is not contemporary or official . Y1B - 17 ( YB - 17 ) . Though still enthusiastic about the Boeing design , the Army Air Corps decided to cut its order for service test YB - 17s from 65 to 13 after the crash of the original Model 299 . On November 20 , 1936 , the Army Air Corps changed the source of funding from normal funding to ' F - 1 ' procurement , and redesignated the plane Y1B - 17 before it even flew . Unlike its predecessor , which had used Pratt & Whitney R - 1690 Hornet radial engines , the Y1B - 17 used the Wright R - 1820 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 - wishbone to single - arm landing gear . On December 7 , 1936 , five days after the first flight of the Y1B - 17 , the brakes on the aircraft fused during landing , and it nosed over . Though damage was minimal , the cumulative impact of this event and the crash of the Model 299 triggered a Congressional investigation . After the crash the Army Air Corps was put in notice : another crash would mean the end of the program . 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 2nd Bomb Group at Langley Field , Virginia . Andrews reasoned that it was best to develop heavy bombing techniques as quickly as possible . Of the thirteen built , one was used for stress 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 spent with the planes entailed eliminating problems with the aircraft . The most important development 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 which led to the loss of the 299 . In May 1938 , the Y1B - 17s ( now redesignated B - 17 ) of the 2nd Bombardment Group , led by the lead plane ' s navigator Curtis LeMay , took part in a demonstration in which they intercepted the Italian liner " Rex " . Coming into contact with the liner while it was still 610 mi ( 982 km ) 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 it could reach 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 Corps from operating more than a hundred miles from the American coast . After three years of flight , no serious incidents occurred with the B - 17s . In October 1940 , they were transferred to the 19th Bombardment Group at March Field . B - 17A ( Y1B - 17A ) . 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 . B - 17B . 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 1 , 200 hp ( 895 kW ) R - 1820 - 51 engines . The small gun turret in the upper nose blister was replaced with a . 30 in ( 7 . 62 mm ) machine gun , its barrel run through a flexible ball socket ; the separate bombardier ' s window was replaced with a flat plexiglass panel in the lower center of the nose combing . During Army Air Corps service , its bulged machine gun blisters were replaced with the more aerodynamic flush side windows used on the B - 17C / D 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 its 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 . B - 17C . 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 ' , similar in appearance and general location on the fuselage , to the " Bola " ventral gondola then being used on the He 111 . Some of the most important additions were self - sealing fuel tank s 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 20 planes to the RAF . Though the Army Air Corps did not consider the B - 17C ready for combat , it was desperately needed in Britain . They were modified Boeing production B - 17C , given the company designation Model 299T . The modifications were the addition of self - sealing tanks and replacement of the single nose gun with 0 . 5 inch Brownings . The twenty planes were placed immediately into frontline service as the Fortress Mk I . In Britain , the plane performed unremarkably . By 1941 September , 39 sorties had made up 22 missions . Nearly half of the sorties were aborted due to mechanical problems . Eight of the twenty were destroyed by September , half to accidents . 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 Mather Army Air Base , CA , on November 2 , 1941 . B - 17D . 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 in ( 7 . 62 mm ) and six 0 . 50 in ( 12 . 7 mm ) 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 - originally nicknamed the " Ole Betsy " by its crew - is undergoing restoration at the National Museum of the United States Air Force in Dayton , Ohio , and is known as " The Swoose " . Former crew member Frank Kurtz named his daughter Swoosie Kurtz after this aircraft . B - 17E . 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 a redesigned vertical stabilizer , originally developed for the Boeing 307 by George S . Schairer . The new fin had a distinctive shape for the time . Because experience had shown that the plane would be vulnerable to attack from behind , both a tail gunner ' s position and powered fully traversable dorsal turret behind the cockpit , each armed with a pair of Browning M2 . 50 cal . machine guns , were added to the B - 17E design . Until this modification , crews had 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 enemy fighters . 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 , directly across the fuselage from each other , for better visibility . In the initial fifth of the production run , the ventral bathtub gun emplacement of the C and D versions was replaced by a remote - sighted Bendix turret , very similar to the unit placed on the B - 25B Mitchell medium bomber of the same period , which proved to be a disappointment in usability , resulting in the remaining E - series aircraft being fitted with a Sperry ball turret , to be used for all succeeding B - 17 versions . 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 , it was 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 . Four known examples of B - 17Es still exist in museums in the 21st century , none of which is currently known to be airworthy . B - 17F . The B - 17F was an upgrade of the B - 17E , although outwardly the types were distinguished only by exchanging the framed nose - glass that had originated with the B - 17B , for a molded one - piece plexiglas cone . Late production " F " series aircraft received a " cheek " - mounted gun on each side of the nose , offset in their horizontal placing with the starboard " cheek " emplacement further forward , 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 , the " F " series 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 of two to four flexible guns were utilized in the field , as sometimes cannibalized from damaged B - 17s ' tail gun positions ( as one example ) , but the problem was not adequately addressed until the introduction of a powered , remotely operated " chin " turret in the final production blocks of the F - series Fortresses , directly derived from its debut on the YB - 40 experimental " gunship " version . By using a stronger undercarriage , the maximum bomb capacity was increased from to . Though this modification reduced cruise speed by , 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 each side of the joint between the inner and outer wing sections . With an extra to the available on the first B - 17Fs , the Tokyo tanks added approximately to the bomber ' s range . 3 , 405 were built : 2 , 300 by Boeing , 605 by Douglas , and 500 by Lockheed ( Vega ) . These included the famous " Memphis Belle " . 19 were transferred to the RAF , where they served with RAF Coastal Command as the Fortress II . Three examples of the B - 17F remain in existence in the 21st century , including the under - restoration " Memphis Belle " . B - 17G . Generally considered the definitive B - 17 design , all changes made in the B - 17F production run were incorporated into the final version . These included a Bendix remotely operated chin turret , an innovation derived from the unsuccessful YB - 40 escort version , bringing defensive armament to 13 . 50 caliber ( half - inch or 12 . 7 mm ) machine guns , and for late production blocks , a revised tail gun position ( referred to as the " Cheyenne " configuration after the modification center where it was introduced ) in which the guns were mounted in a remotely operated turret . Some 8 , 680 were built , and dozens were converted for several different uses : Fortress III . Eighty - five B - 17Gs were transferred to the Royal Air Force , where they received the service name Fortress III . Three went to Coastal Command in the Azores fitted with radar before reuse with Meteorological squadrons . The rest were operated by two squadrons of Bomber Command ' s No . 100 Group RAF at RAF Sculthorpe from February 1944 , where they were used to carry electronic countermeasure s to confuse and jam enemy radar in support of bombing missions . These Fortress III ( SD ) would carry extensive array of equipment : the Monica tail - warning receiver , the Jostle VHF jammer , Airborne Grocer air - interception jammers ; Gee and LORAN for navigation and an H2S radar replacing the chin turret . They were also used as decoys during night bombing attacks . They took part in various such operations until the units were disbanded in July 1945 . XB - 38 . 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 19 May 1943 . 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 16 June 1943 . 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 . Allison engines were also considered to be more badly needed for constructing fighter aircraft . YB - 40 . 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 atop the radio operator ' s position between the forward dorsal turret and the waist guns , where only a single flexibly mounted Browning M2 gun had been ; and the single 0 . 50 in ( 12 . 7 mm ) machine gun at each waist station was replaced by a pair of 0 . 50 in ( 12 . 7 mm ) guns , of basically the same twin - mount design as the tail guns used . In addition , the bombardier ’ s equipment was replaced with two 0 . 50 in ( 12 . 7 mm ) machine guns in a remotely operated ‘ 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 armed " gunship " 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 . B - 17E 41 - 2595 was chosen for the conversion . 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 to maintain , due to lack of spare parts for the Cyclone engines , and was sent back to the United States , where it was based in Bangor , Maine , and flew a cargo route to Scotland until the end of the war . It was sold to a local dealer for scrap , but the airframe survived , and is currently being restored in Illinois . 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 by the USAAF 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 variant designation was the F - 9C , which was given to ten B - 17G , converted in a similar fashion to the previous planes . Those surviving in 1948 were at first redesignated RB - 17G ( " R " indicating ' reconnaissance ' ) . BQ - 7 Aphrodite . 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 , 070 kg ) of Torpex high explosive and enough fuel for a range of 350 mi ( 563 km ) they were used to attack U - boat pens , V - 1 missile sites , and other bomb - resistant fortification s . The BQ - 7s would be taken aloft by two volunteer crew members , who would take it up to 2 , 000 ft ( 610 m ) , 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 ft ( 30 m ) 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 ( USN ) received 48 B - 17 ' s towards the end of World War II , renamed PB - 1 and used for maritime patrol missions . Post - war , the USN acquired 31 more B - 17G ' s , renamed PB - 1W , and fitted with AN / APS - 20 radar for Airborne Early Warning equipment and procedure development . The Naval Air Material Center ’ s Naval Aircraft Modification Unit ( NAMU ) at Johnsville , Pennsylvania modified the B - 17s to PB - 1W specification by sealing up the bomb bay doors and installing 300 gallon drop tanks on each wing , in addition to the “ Tokyo Tanks ” mounted in the outer wings , holding a total of 3 , 400 gallons of fuel , giving the PB - 1W an endurance of 22 + hours . Initially PB - 1W ' s retained the natural metal finish with a protective wax coat , but later the PB - 1Ws were painted gloss Navy Blue overall . The scanner for the one - megawatt AN / APS - 20 Seasearch S - band Radio Detection and Ranging ( RADAR ) , manufactured by Hazeltine Corporation / General Electric , was ventrally mounted in a bulbous housing below the redundant bomb bay , with the RADAR relay transmitter , Identification friend or foe ( IFF ) , Radio Direction Finder ( RDF ) , Instrument Landing System ( ILS ) , and LOng RAnge Navigation ( LORAN ) also being installed during conversion . The conversion introduced the following changes : - The crew for USN PB - 1Ws consisted of 6 officers , ( Pilot in Command , Second in Command , Navigator , CIC Officer , and 2 RADAR Operators / Controllers ) and 5 enlisted men ( Plane Captain ( now referred to as Crew Chief ) , 2nd Mechanic , Electronics Technician , and 2 Radio Operators ) . First delivered to Patrol Bomber Squadron 101 ( VPB - 101 ) in the spring of 1946 , the Navy was eventually to have twenty two , out of thirty one post - war B - 17s , fully upgraded to PB - 1W standard . Late in 1946 , VPB - 101 would move to NAS Quonset Point , Rhode Island , and be redesignated Airborne Early Warning Development Squadron Four ( VX - 4 ) . SB - 17G and PB - 1G . From 1943 to 1948 , as part of Dumbo missions , 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 .