The B-17 Flying Fortress was perhaps the most well-known American heavy bomber of the Second World War. It achieved a fame far beyond that of its more-numerous stablemate, the Consolidated B-24 Liberator. A total of 12,677 Fortresses was built before production came to an end.

In August of 1944, the B-17 equipped no less than 33 overseas combat groups. It was to achieve lasting fame in the daylight precision-bombing campaign over Germany in 1943, 1944, and 1945. It achieved a reputation as being capable of absorbing a tremendous amount of battle damage and still continuing to fly. In later variants, it had an exceptionally-heavy defensive armament. It had an excellent high-altitude performance. It was able to win the affection of the crews who flew in it, since it was often able to bring them home safely when other aircraft would have fallen. However, the B-17 generally had a performance inferior to that of its B-24 stablemate and it could not carry nearly as large a bomb load. In typical missions over Europe, B-17s usually carried a bombload only as large as that which a twin-engined Mosquito could carry.

B-17s dropped 640,036 tons of bombs on European targets during the war, as compared to 452,508 tons dropped by the Liberator and 463,544 tons dropped by all other US aircraft. Boeing records claim that the Fortress destroyed 23 enemy aircraft per thousand sorties as compared to 22 for Liberators, eleven by US fighters, and 3 by all US light and medium bombers. However, the "kill" claims by both Fortress and Liberator gunner crews are probably greatly exaggerated, largely because the same enemy aircraft was being fired at by many different people. Approximately 4750 B-17s were lost on combat missions, which is about one out of three of all B-17s built.

The origin of the Boeing Fortress can be traced to a February 1934 Army Air Corps requirement for a bomber with a range of 5000 miles at 200 mph while carrying a bombload of 2000 pounds. This became known as "Project A", and was more of a feasibility study than it was a serious proposal for a production bomber. However, there was always a possibility that production examples would be ordered if the design proved successful. Both Martin and Boeing submitted preliminary designs in response to the "Project A" requirement. The Martin project was cancelled before anything could be built, but the Boeing design (assigned the company designation of Model 294) was awarded a contract for a single example under the designation XBLR-1. The XBLR-1 was later redesignated XB-15.

In May of 1934, the Army announced another bomber competition. This time, it was for a multi-engined bomber capable of carrying a ton of bombs at more than 200 mph over a distance of 2000 miles. As opposed to the "Project A" requirement, this Army requirement envisaged from the start that the winning design would have a production run of as many as 220 planes. Several manufacturers (including Boeing) were invited to submit bids, with the entries being flown at Wright Field in a final competition to select the winner. Preliminary work by Boeing on the design began on June 18, 1934. Boeing engineers came up with what was basically a scaled-down version of the Model 294. Like the Model 294, it was to be powered by four engines. Four-engined bombers were a novelty at the time, most contemporary bomber designs having only two engines. Construction began on August 16, 1934 under the company designation Model 299.

The Model 299 was based heavily on the company's experience with the all-metal Model 247 commercial airliner. It was basically a marriage between the aerodynamic and structural features used by the Model 247 and the basic four-engined format used by the Model 294 bomber. The aircraft was to be powered by four 750 hp Pratt & Whitney R-1690-E Hornet nine-cylinder air-cooled radials, each driving a three-bladed propeller. The large, thick-section wing was to be mounted low on the cylindrical-section fuselage. The main landing gear was to retract forward into the inner engine nacelles, with the lower edge of the wheel protruding into the airstream.

The Model 299 aircraft was painted with the civilian registration X-13372, since it was a company-owned aircraft. It carried a crew of 8, a pilot, copilot, bombardier, navigator/radio operator, and four gunners. There were four blister-type flexible machine gun stations, each of which could accommodate a 0.3-inch or 0.5-inch machine gun. One was in a dorsal position in the fuselage just above the wing trailing edge, a second was in a ventral fuselage position just behind the wing trailing edge, and a blister was mounted on each side of the rear fuselage in a waist position. There was an additional station for a machine gun in the nose. All of the guns were manually swung. Up to eight 600-pound bombs could be carried internally. Loaded weight was 43,000 pounds.

In order to prevent damage by wind to the tail surfaces while the plane was on the ground, the elevators were locked in position. Before takeoff, the pilot would unlock the tail surfaces by releasing a spring lock in the cockpit.

First flight of the Model 299 took place on July 28, 1935 at Seattle with Boeing test pilot Leslie R. Tower at the controls. According to legend, a reporter having seen the 299 for the first time remarked, "Why, it's a flying fortress!". The name stuck.

After a short period of factory testing, the Model 299 was flown by Boeing test pilot Leslie Tower and three other crewmen out to Wright Field on August 20 for Air Corps evaluation. During this flight, it flew the 2100 miles nonstop at an average speed of 232 mph at an average altitude of 12,000 feet, breaking all records for the distance.

The prototype was submitted to the Army as Model X-299, but the Army objected to the designation as being too similar to its experimental military project numbers, so it was officially changed to B-299.

The competitors of the B-299 were the Martin 146 and the Douglas DB-1, which were both twin-engined designs. The Model 299 surpassed all the Army requirements for speed, climb, range and bombload. The Army decided to purchase 65 service test examples under the designation YB-17.

On October 30, 1935, the Model 299 crashed during takeoff at Wright Field and burned. Three of the crewmen managed to crawl out of the wreckage with only minor injuries, but pilot Ployer P. Hill (chief of Wright Field's Flight Testing Section) and Boeing test pilot Leslie Tower (who was riding as an observer) both died later of their injuries

after being dragged from the burning aircraft. An investigation later showed that the crash was caused by the crew forgetting to unlock the tail surfaces before takeoff, the aircraft losing control immediately after leaving the ground and crashing.

Although the aircraft was blameless in the crash, the Air Corps got cold feet about the wisdom of acquiring so many YB-17s with the limited funds that were available and cut their order back to to only 13 examples on January 17, 1936. The designation was changed to Y1B-17 on November 20, 1936, the "Y1" designation indicating that they were purchased from "F-1" funds rather than from regular appropriations.

As insurance, the Army decided at the same time to order 133 examples of the competing twin-engined Douglas DB-1 under the designation B-18. The B-18 was substantially slower than the Flying Fortress, had a shorter range, carried fewer bombs, and had a poorer defensive armament. However, it was only half as expensive as the B-17 and since the B-18 was based on a proven design (the DC-2 commercial airliner), the amount of risk was deemed to be smaller.

The wreckage of the B-299 was salvaged and a section of the fuselage containing the the side blisters was used at Wright Field for the evaluation of new types of gun mounts.

The Model 299 never carried a US Army serial number.

Specification of Model 299:
Four Pratt & Whitney R-1690E S1EG Hornet radials rated at 750 hp at 2250 rpm at 7000 feet.
Maximum speed 236 mph at 10,000 feet.
Cruising speed 204 mph.
Service ceiling 24,620 feet.
Range 2040 miles with 2573 pounds of bombs.
Maximum range 3101 miles.

Dimensions:
Wingspan 103 feet 9 3/8 inches
length 68 feet 9 inches
height 14 feet 11 15/16 inches
wing area 1420 square feet.

Weights:
21,657 pounds empty
32,432 pounds normal loaded
38,053 pounds maximum
Armed with five 0.30-inch machine guns, with one gun in each of nose, dorsal, ventral, and two waist positions.
A maximum of eight 600 pound bombs could be carried in an internal bomb bay.

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