The Boeing B-17 Flying Fortress is a four-engine heavy bomber developed in the 1930s for the United States Army Air Corps.
Competing against Douglas and Martin for a contract to build 200 bombers, the Boeing entry (prototype Model 299/XB-17) outperformed both competitors and exceeded the Air Corps’ performance specifications.
Although Boeing lost the contract (to the Douglas B-18 Bolo) because the prototype crashed, the Air Corps ordered 13 more B-17s for further evaluation.
From its introduction in 1938, the B-17 Flying Fortress evolved through numerous design advances, becoming the third most produced bomber of all time, behind the four engine Consolidated B-24 Liberator and the multirole, twin engine Junkers Ju 88.
The Model 299 was the original bomber design built by Boeing to fulfill an August 1934 requirement 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).
Though still enthusiastic about the Boeing design, despite it being disqualified from the fly-off contest following the crash of the Model 299 prototype, the Army Air Corps cut its order from 65 service test YB-17s to just 13.
On November 20, 1936, the bomber’s normal acquisition funding was changed to “F-1”, and the heavy YB-17 bomber was redesignated “Y1B-17”, as a result.
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, Army Air Corps leaders decided that the bomber was exceptionally robust and that there would be no need for static testing.
Instead, it was used as a test bed for enhancing engine performance on the new bomber.
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, globe like, machine gun turret used in the Y1B-17’s upper nose blister was replaced with a .30 calibre (12.7 mm) machine gun, its barrel run through a ball socket in the ten-panel Perspex nose glazing.
This was held in place by both the socket’s strength combined with a flexible interior support strap, which later became an aluminium reinforced window pane.
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 machine gun blisters were replaced with teardrop-shaped, slide-out Perspex window panels flush with the fuselage, and the ventral blister was replaced by a lower metal housing dubbed a “bathtub turret”, similar in appearance and general location on the lower fuselage, to the Bola ventral gondola being used on Germany’s He 111P medium bomber.
The most important additions made to the “C” series were self-sealing fuel tanks and defensive armour plate added to vital areas.
Though changes in the design made the Army Air Force decide that the B-17D was worthy of a new sub designation, the B-17C and B-17D were very similar.
In fact, both were given the same sub designation (299H) by Boeing.
Minor changes were made, both internally and externally.
The B-17E (299-O) was an extensive redesign of the previous B-17D.
The most obvious change was the larger, completely new vertical stabilizer, originally developed for the Boeing 307 by George S. Schairer.
The new fin had a distinctive shape for the time, with the opposite end of the fuselage retaining the ten panel bombardier’s nose glazing from the B-17D.
The B-17F was an upgrade of the B-17E.
Outwardly, both types were distinguished primarily by the ten-panel fully-framed nose glazing on the “E” series.
A moulded, one-piece or two-piece all plexiglass nose cone replaced this framed glazing on the “F” series
(The two-piece cone had a nearly-transparent diagonal seam).
B-17G & Variants
Troop transport version, capable of carrying 64 troops.
Rescue version, later redesignated B-17H, featuring a A-1 lifeboat under the fuselage.
After World War II, armament on the B-17Hs was removed, it was reinstated when the Korean War began.
Special duty training version
This designation was given to one B-17F and one B-17G. They were used by the U.S. Navy for various test projects.
This designation was given to 17 B-17Gs used by U.S. Coast Guard as air-sea rescue aircraft.
This designation was given to 31 B-17Gs used by the U.S Navy as the first airborne early warning aircraft (AWACS).
Eighty-five B-17Gs were transferred to the RAF, where they received the service designation Fortress III.
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.
Prior to the introduction of the P-51 Mustang, a B-17 “gunship” 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 an upward firing single or double Browning M2 had been mounted, and a 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 used for the tail guns.
In addition, the bombardier’s equipment was replaced with twin 0.50 in (12.7 mm) machine guns in a remotely operated “chin” turret directly under the bombardier’s position, augmenting the existing “cheek” machine guns, the bomb bay was converted to a .50 calibre magazine.
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.
F-9 Flying Fortress
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’).
FB-17 was the 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 (9,070 kg) of Torpex high explosive and enough fuel for a range of 350 mi (563 km) they were used to attack Nazi U-boat pens, V-1 missile sites, and other bomb-resistant fortifications.
2,000 mi (3,219 km, 1,738 nmi) with 6,000 lb (2,700 kg) bomb load
3,750 mi (6,040 km, 3,260 nmi)
35,600 ft (10,850 m)
Rate of climb
900 ft/min (4.6 m/s)
38.0 lb/sq ft (185.7 kg/m2)
0.089 hp/lb (150 W/kg)
13 × .50 in (12.7 mm) M2 Browning machine guns in 9 positions
(2 in the Bendix chin turret, 2 on nose cheeks, 2 staggered waist guns, 2 in upper Sperry turret, 2 in Sperry ball turret in belly, 2 in the tail and one firing upwards from radio compartment behind bomb bay)