List of Boeing B-17 Flying Fortress variants

The Model 299 was the original aircraft 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 (910 kg) of bombs 2,000 mi (3,200 km) at 200 mph (320 km/h).

Despite the crash and its much higher unit cost, the Army Air Corps leaders was impressed by its performance, so Boeing was awarded a development contract.

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.

Most of the time spent with the bombers entailed eliminating problems with the aircraft but the most important development was the use of a detailed checklist reviewed by the pilot and copilot prior to each takeoff.

In May 1938, the Y1B-17s (now redesignated as B-17) of the 2nd Bombardment Group, led by the lead bombers' navigator Curtis LeMay, took part in a demonstration in which they intercepted the Italian liner Rex.

However, when one of the Y1B-17s survived an inadvertent violent spin during a flight in a thunderhead, Army Air Corps leaders decided that there would be no need for static testing.

A successive series of General Electric-manufactured turbochargers would equip B-17s as standard items,[4] starting with the first production model, allowing it to fly higher and faster than the Y1B-17.

During Army Air Corps service, the bulged teardrop-shaped machine gun blisters were replaced with flush-mounted Perspex side windows of the same type used in the B-17C/D series.

In addition, some "B" series Fortresses also had ventral "bathtub turrets" (see the "C/D" section below) installed, replacing their lower, teardrop-shaped gun blisters.

Many of these RB-17B aircraft, along with at least one still-airworthy YB-17, were stationed at Sebring Airfield, where the exterior scenes were filmed for the Warner Bros. war drama Air Force (1943), directed by Howard Hawks, and starring (among others) John Garfield, Arthur Kennedy, Gig Young, and Harry Carey.

Their guns froze-up at altitude and were unable to protect the Fortresses from attack and their effectiveness as bombers was also limited, largely because of problems with achieving an adequate level of bombing accuracy.

The most obvious change was the larger, completely new vertical stabilizer, originally developed for the Boeing 307 Stratoliner, and the addition of a tail gunner.

Until these modifications, specific maneuvers were needed against attacks from behind, including yawing the bomber laterally, allowing the waist gunners to alternate bursts at enemy fighters.

The combined weight, when fully combat-loaded, of the four rear gunners and their heavy .50 caliber ammunition, moved the bomber's center of gravity rearward.

Late production "F" series aircraft received substantially-enlarged bulged "cheek" mounts for their .50 caliber machine guns, on each side of the nose.

A number of other modifications were made, including reinstalling external bomb racks, but because both rate-of-climb and high-altitude flight performance suffered, these were rarely used and were removed.

The earliest B-17Gs lacked the "cheek" machine gun mounts, as it was believed that the chin turret provided sufficient forward firepower; they were quickly reintroduced.

While it showed a slightly higher top speed, after just a few flights it had to be grounded due to a problem with engine manifold joints leaking exhaust gases.

Following this problem being resolved, testing continued until the ninth flight on 16 June 1943 when the inboard starboard engine caught fire, and the crew bailed out.

It proved a difficult aircraft to maintain, due to lack of spares for the Cyclone engines, and was returned to the United States, where it was based in Bangor, Maine, and flew a cargo route to Scotland until the end of the war.

An uncertain number of additional airframes were converted to a similar configuration to the F-9, but differed in minor details of their cameras, and received the designation F-9A.

Loaded with 20,000 lb (9,100 kg) of Torpex high explosive and enough fuel for 350 mi (560 km), they were to be used to attack Nazi U-boat pens, V-1 flying bomb sites, and bomb-resistant fortifications.

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.

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).

The USCG, always quick to take advantage of anything they could get inexpensively, requested that the Army Air Force loan eighteen of the bombers to the Coast Guard.

The Coast Guard adopted the A-1 lifeboat for many of its PB-1Gs (the naval designation for the Flying Fortress).Furthermore the PB-1Gs were equipped with an ASV radar to assist in the SAR operations.

Additionally, these aircraft were also used for the International Ice Patrol while another of the versatile PB-1Gs was modified to carry a nine-lens, 1.5 million dollar, aerial camera for mapping purposes.