Boeing B-17 Flying Fortress

Introduction

The B-17 Flying Fortress is often neglected by histories of the American heavy bomber force that ended the Second World War yet it was this aircraft that the early bomber crews used to develop the tactics and technologies that culminated in The Big One. A total of 945 Fortresses was built before production came to an end in August 1943. Despite its brief service and limited numbers, the B-17 achieved a reputation as being capable of absorbing a tremendous amount of battle damage and still continuing to fly. Significantly, by the standards of its day, 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.

Early Development

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 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 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. 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. 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.

Specification of Boeing XB-17

Four Pratt & Whitney R-1690E S1EG Hornet radials rated at 750 hp at 2250 rpm at 7000 feet. Performance: 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. Armament: 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.

Variants

Boeing Y1B-17

The Y1B-17 was the initial service test version of the B-17, thirteen of which had been ordered on January 17, 1936. It had initially been designated YB-17, but this was changed to Y1B-17 on November 20, 1936, indicating procurement from "F-1" funds rather than from regular appropriations. The Y1B-17 was basically similar to the Model 299, but had four Wright GR-1830-39 (G2) Cyclone radials in place of the Pratt & Whitney Hornet radials of the Model 299 prototype. The Cyclone was to remain the standard powerplant all throughout the long production run of the Fortress. The crew was reduced to six, and minor changes were made in armament details and in the undercarriage. Perhaps the most readily-noticeable difference was in the the main landing gear, which now had only one leg rather than two. A long carburetor intake on top of the engine nacelles distinguished the Y1B-17 from later models. The first Y1B-17 (36-149) flew on December 2, 1936. All Y1B-17s were delivered between January 11 and August 4, 1937. Twelve of the Y1B-17s were delivered to the 2nd Bombardment Group based at Langley Field, Virginia for evaluation. The thirteenth Y1B-17 was delivered to Wright Field for experimental tests. At this time, the dozen Y1B-17s of the 2nd Bombardment Group comprised the entire heavy bombardment strength of the United States.

The 2nd Bombardment Group spent its time working out the bugs in the B-17. One of the recommendations that they came up with at an early stage was the use of a check list that the pilot and copilot would go through together before takeoff, hopefully preventing accidents such as the one which resulted in the loss of the Model 299. The author of this policy was a young Lieutenant named Curtis Emerson LeMay. Lieutenant LeMay was also the chief navigator for the first international flight by a U.S. strategic bomber group when six planes of the 2nd Bombardment group took part in a good will flight from Langley to Buenos Aires, Argentina, taking off from Langley on February 15, 1938 and returning on February 27. They covered a total of 12,000 miles without serious incident.

In May 1938, Curtis LeMay was again head navigator when Y1B-17s of the Langley-based 2nd Bombardment Group took part in a demonstration in which they "intercepted" the Italian liner *Rex* while it was still 700 miles out to sea. This was meant not only as a demonstration of the Y1B-17's superior range and navigational capabilities, but was also meant to show how useful the plane could be in attacking an enemy invasion force before it came close enough to American shores to do any damage. The Navy was not at all amused by this particular demonstration, and was furious about what it perceived to be an Army intrusion into the Navy's particular mission. Shortly thereafter, a War Department order came down restricting the activities of the Army Air Corps to within a 100-mile range of the US shoreline. The Y1B-17s flew for three years without a serious accident, and were transferred to the 19th Bomb Group at March Field in October 1940.

Specification of Boeing Y1B-17:

Four Wright R-1820-39 Cyclone radials rated at 930 hp for takeoff, 850 hp at 5000 feet, 775 hp at 14,000 feet. Performance: Maximum speed 256 mph at 14,000 feet. Landing speed 70 mph. Cruising speed 217 mph at 70 percent power. Service ceiling 30,600 feet. An altitude of 10,000 feet could be attained in 6.5 minutes. Normal range 1377 miles. Range with 4000 pounds of bombs was 2400 miles and 3320 miles with no bombs. Dimensions: Wingspan 103 feet 9 3/8 inches, length 68 feet 4 inches, height 18 feet 4 inches, wing area 1420 square feet. Weights: 24,465 pounds empty, 34,880 pounds normal loaded, 42,600 pounds maximum. Armament: Armed with five 0.30-inch machine guns with 1000 rpg. One gun was mounted in each of nose, dorsal, ventral, and two waist positions. A maximum bombload of 8000 pounds could be carried in an internal bomb bay.

Boeing B-17B

The B-17B was the first production version of the B-17 series. Outwardly, the B-17B differed from the Y1B-17 only in having a revised rudder with larger area, larger wing flaps, and a revised nose that eliminated the greenhouse gun turret in the upper nose and the belly bomb-aiming window in the lower nose. The upper nose turret was replaced by a simple socket for a 30-inch flexible machine gun in the extreme tip of the nose. The bomb-aiming window was replaced by an optical flat in the lower part of the Plexiglas nose fairing. The revised nose resulted in a decrease in overall length of 7 inches. A small plastic dome was added to the cabin roof. More-powerful R-1820-51 engines were fitted which delivered a maximum power of 1200 hp for takeoff and 900 hp at 25,000 feet. Internally, many systems were changed and crew members were relocated. The brakes were changed from pneumatic to hydraulic.

The famous Norden bombsight was mounted above the bomb-aiming window. The Norden bombsight was a gyro-stabilized bomb sight originally developed by Carl L. Norden and Capt. Frederick I. Entwistle. It was capable of quickly calculating the plane's forward velocity and drift and making corrections in order to achieve a hit. In later versions, the Norden bombsight was connected with the autopilot, and actually flew the plane during the final run in to the target. In the press releases of the day, the bombsight was claimed to be so accurate that it could "put bombs in a pickle barrel". The Norden bombsight was considered so secret that it was installed, carefully covered, in the aircraft only immediately before takeoff and was taken out immediately after landing, always under the supervision of an armed guard.

The first B-17B (38-211) flew for the first time at Seattle on June 27, 1939. 39 B-17Bs were built in a single run at Boeing. All 39 of the B-17Bs were delivered to the USAAC between July 29, 1939 and March 30, 1940. The B-17Bs were issued to the 2nd, 7th, and 19th Bombardment Groups, except for the first example which was retained at Wright Field for tests. A B-17B serving with the 41st Reconnaissance Squadron of the 2nd Bomb Group based in Newfoundland attacked a U-boat on October 27, 1942. Although the U-boat was undamaged in the attack, this incident was the first in which bombs were dropped in anger by the Army Air Forces in action against German forces.

Specification of Boeing B-17B

Four Wright R-1820-51 Cyclone radial engines rated at 1200 hp for takeoff. Performance: Maximum speed 292 mph at 25,000 feet. Service ceiling 24,620 feet. Maximum range 3101 miles. Dimensions: Wingspan 103 feet 9 3/8 inches, length 67 feet 10.2 inches, height 15 feet 5 inches, wing area 1420 square feet. Weights: 27,652 pounds empty, 37,997 pounds gross, 46,178 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.

Boeing B-17C

A further 38 Fortresses were ordered by the Army in 1939, designated the B-17C by the Army. The B-17C differed from the earlier B-17 versions in having the gun blisters removed from the sides of the rear fuselage and replaced by flush, oval-shaped windows. Each of the oval windows had a port for a single 0.50-inch machine gun cut into its edge. The belly gun blister was replaced by a larger metal "bathtub" housing carrying a single 0.50-inch machine gun. The dorsal blister located at the radio operator's position behind the pilot's compartment was replaced by a flush panel into which a single socket for a 0.50-inch machine gun was cut. The nose gun mounting was changed from a single socket in the forward window to six sockets mounted in side windows. The nose 0.30-inch machine gun could be fired from any one of these sockets. Self-sealing fuel tanks and armor protection for the crew were introduced. The engines were four supercharged 1200 hp Wright GR-1820-65 (G-205A) Cyclones. Maximum weight was increased to 49,650 pounds. The first B-17C flew on July 21, 1940 and delivery of the B-17C to the USAAC was completed by November 29. However, all USAAC machines were returned to Boeing in January 1941 to be upgraded to B-17D standards.

Specification of B-17C:

Four Wright GR-1820-65 (G-205A) Cyclone radials rated at 1200 hp for takeoff, 100 hp at 25,000 feet. Performance: Maximum speed 323 mph at 25,000 feet. Cruising speed 250 mph. Landing speed 84 mph Service ceiling 37,000 feet. Climb to 10,000 feet in 7.5 minutes. Range 2400 miles with 4000-pound bombload. Maximum range 3400 miles. Dimensions: wingspan 103 feet 9 3/8 inches, length 67 feet 10.6 inches, height 15 feet 5 inches, wing area 1420 square feet. Weights: 29,021 pounds empty, 39,320 pounds gross, 49,650 pounds maximum. Armament: Armed with four 0.50-inch machine guns and one 0.30-inch machine gun. One each of 0.50-inch guns were carried in dorsal, ventral, and two waist positions, and there was one 0.30-inch machine gun which could be fired from any one of six sockets in the nose. A maximum of 4800 pounds of bombs could be carried in an internal bomb bay.

Boeing B-17D

Forty-two more B-17Cs were ordered on April 17, 1940. However, these planes were sufficiently different from the original batch of B-17Cs that the Army decided to give them a new designation of B-17D. Externally, the B-17D differed from the C in having a set of engine cowling flaps to improve the cooling. Internal changes included electrical system revisions and the addition of a tenth crew member. The B-17D had paired guns in the belly and top positions, bringing the total armament to one 0.30-inch and six 0.50-inch machine guns. The external bomb racks were deleted. The first B-17D flew on February 3, 1941. The B-17Ds were delivered to the Army from February to April of 1941. First priority was given to overseas units, with most of the B-17Ds going to units based in Hawaii or in the Philippines. Starting in March 1941, the Army began to paint its B-17s in olive drab and grey camouflage paint and by the end of the year virtually all B-17s were camoflaged.

Specification of B-17D:

Four Wright GR-1820-65 (G-205A) Cyclone radials rated at 1200 hp for takeoff, 1000 hp at 25,000 feet. Performance: Maximum speed 318 mph at 25,000 feet. Service ceiling 37,000 feet. Dimensions: wingspan 103 feet 9 3/8 inches, length 67 feet 10.6 inches, height 15 feet 5 inches, wing area 1420 square feet. Weights: 30,963 pounds empty, 39,319 pounds gross. Armament: Armed with six 0.50-inch machine guns and one 0.30-inch machine gun. A single 0.50-inch gun was carried in each of the two waist positions, and a pair of 0.50-inch machine guns were mounted in each of the dorsal and ventral positions. There was one 0.30-inch machine gun which could be fired from any one of six sockets in the nose. A maximum of 4800 pounds of bombs could be carried in an internal bomb bay.

Boeing B-17E

The B-17E was the last Boeing-built production version of the Flying Fortress and was originally designed to correct some of the deficiencies in the earlier Fortresses that had been brought to light as a result of experience with the earlier B-17s. The B-17E was first ordered on August 30, 1940, and the first prototype took to the air on its maiden flight on September 5, 1941. The B-17E introduced a completely new rear fuselage with a manually-operated turret housing two 0.50-inch machine guns fitted in the extreme tail. In order to accommodate the tail gun, the fuselage of the B-17E was a full six feet longer than that of the D. A Bendix electrically-powered turret containing two 0.50-inch machine guns was installed on the upper fuselage immediately behind the flight deck. This turret was usually operated by the flight engineer. The oval waist positions were replaced by rectangular apertures with removable windows. A single 0.50-inch machine gun could be mounted behind each of these windows. A power-operated belly turret replaced the ventral "bathtub" housing of the B-17D. This turret was remotely-controlled by a system of mirror periscopic sights from a Plexiglas bubble below the waist hatches. In order to achieve better stability during the bomb run, the span of the horizontal tailplane was increased, the vertical tail was greatly increased in area, and a long dorsal fin was fitted in front of the tail.

Despite the improvements included in the B-17E, the type was already doomed when the first example flew on September 5, 1941. The collapse of the U.K. on June 19, 1940 had caused the U.S. to adopt a new warplan, designated AWPD-1. This took into account the demonstrated fact that no foreigna irbases were available in any bombing campaign against Germany and that the bombing offensive would have to be carried out from the Zone of the Interior, that is, from bases within mainland U.S.A. This meant that the performance of the B-17, even in its modernized form, was totally inadequate and that the type was, at best, a training aircraft for the later, longer-range bombers that AWPD-1 demanded. These were, of course, the B-36. Boeing was instructed to stop all further design work on the B-17 and concentrate on the B-29 that was seen as an interim bomber until the Consolidated B-36 was available. Although B-17E production continued, this was more or less to keep Boeing's production line running until B-29 construction could take over.

The B-17E was first delivered to combat units of the 7th Bombardment Group in November 1941. The periscope sight for the remotely-controlled dorsal turret proved difficult to use in practice, and starting with the 113th B-17E, the remotely-controlled turret was replaced by a Sperry ball turret, inside of which a gunner sat all curled up in the foetal position, swiveling the entire turret as he aimed the two guns. With his left eye peering through a sight, he controlled the movement of the guns by hand and foot pedals. There was precious little space inside the turret — ball turret gunners had to be very small men. The B-17E normally carried a crew of ten — pilot, copilot, bombardier, navigator, flight engineer, radio operator, tail gunner, belly gunner, and two waist gunners. The nose gun was operated by either the navigator or the bombardier when they were not occupied by their primary duties, and the dorsal turret was normally operated by the flight engineer. The last B-17E rolled off the production line at Boeing on August 28, 1943, a total of 812 having been built.

Specification of Boeing B-17E Fortress

Four Wright R-1820-65 Cyclone radials rated at 1200 hp for takeoff and 1000 hp at 25,000 feet. Performance: Maximum speed 318 mph at 25,000 feet. cruising speed 195-223 mph. Landing speed 70 mph Service ceiling 36,600 feet. Normal range 2000 miles with 4000 pounds of bombs. Maximum range 3300 miles. Initial climb rate 1430 feet per minute. An altitude of 5000 feet could be attained in 7 minutes. Dimensions: wingspan 103 feet 9 3/8 inches, length 73 feet 10 inches, height 19 feet 2 inches, wing area 1420 square feet. Weights: 32,350 pounds empty, 40,260 pounds gross, 53,000 pounds maximum. Fuel: Normal fuel load was 2490 US gallons, but extra fuel tanks could be installed which raised total fuel capacity to 3612 US gallons. Armament: Specified defensive armament was as follows: one 0.30-inch machine gun which could be mounted on any one of six ball-and-socket mounts in the extreme nose. One Sperry No. 645473E power turret in the dorsal position with two 0.50 Browning M2 machine guns with 500 rounds per gun. One Sperry No. 654849-J power turret in ventral position with two 0.50-inch Browning machine guns with 500 rounds per gun. One 0.50-inch Browning M2 machine gun is each of the two waist windows, 400 rounds per gun. Two 0.50-inch M2 Browning machine guns in the tail position, with 500 rounds per gun. Maximum bomb load was 26 100-pound bombs, or 16 300-pound bombs, or 12 500-pound bombs, or 8 1000-pound bombs, or 4 2000-pound bombs.

+++ Boeing B-17F

By mid-1943 it was becoming apparent that the B-29 was falling steadily further behind schedule and that the smooth transition from the B-17 to the B-29 was not going to take place. With B-17 production at Boeing winding down and the bomber losses in Russia rising slowly but steadily, it was apparent that additional B-17s would be needed. The problem was where to build them. Boeing was heavily committed to building the B-29, Consolidated to the ultra-secret B-36. Douglas was building C-47 and C-54 transports as well as SBDs for the Navy. Lockheed was deeply committed to the P-38, P-49 and Constellation programs while North American was building B-25 bombers and a variety of trainers. Eventually, it was decided that the Douglas plant at Long Beach, California would undertake began production of the B-17F. The first Douglas-built B-17F of 605 that were to be completed by the plant was delivered in July 1943.

The key external feature distinguishing a B-17F from an E-model was the deletion of the astrodome between the cockpit and the nose. This had been done to make room for a twin .50 caliber machine gun mount in the upper part of the nose transparency. Two additional .50s were placed in cheek mounts, one either side of the nose. The nose bulkhead was heavily armored, providing the cockpit crew with badly-needed protection. The single waist guns were replaced by twin .50s. The added weight was accommodated by the installation of Wright R-1820-97 Cyclones, which could offer a 1380 hp. Revisions to the engine cowlings were required to make it possible to feather the wider propeller blades. A stronger undercarriage was installed which allowed the maximum weight to increase to 65,000 pounds, and later to 72,000 pounds. In late 1943, Lockheed Vega joined the program, delivering an additional 505 B-17Fs.

++++Specification of B-17F:

Four Wright R-1820-97 Cyclone radials rated at 1380 hp for takeoff and 1200 hp at 25,000 feet. Maximum speed 299 mph at 25,000 feet, 325 mph at 25,000 feet cruising speed 200 mph. Landing speed 90 mph An altitude of 20,000 feet could be attained in 25.7 minutes. Service ceiling 37,500 feet. Range 1300 miles with 6000 pounds of bombs, maximum range 2880 miles. A range of 4420 miles at 5000 feet could be attained with 3612 gallons of fuel. Dimensions: Wingspan 103 feet 9 3/8 inches, length 74 feet 9 inches, height 19 feet 1 inches, wing area 1420 square feet. Weights: 34,000 pounds empty, 40,437 pounds loaded, 56,500 pounds maximum. Fuel: Normal fuel load was 2520 US gallons, but extra fuel tanks could be installed which raised total fuel capacity to 3612 US gallons. Armament: Specified defensive armament was as follows: two.50 machine guns in a nose mount and two in cheek mounts, all with 500 rounds of ammunition. One Sperry No. 645473E power turret in dorsal position with two 0.50 Browning M2 machine guns with 500 rounds per gun. One Sperry No. 654849-J power turret in ventral position with two 0.50-inch Browning machine guns with 500 rounds per gun. Two 0.50-inch Browning M2 machine gun is each of the two waist windows, 400 rounds per gun. One ball and socket mount was fitted to the roof of the radio operator's compartment for a 0.50-inch Browning M2 machine gun. Two 0.50-inch M2 Browinging machine guns were installed in the tail position, with 500 rounds per gun. Total of 15 .50 machine guns

Combat Career of the B-17

In November 1942, B-17E aircraft equipped the 2nd, 7th, 19th, 35th 305th and 306th Bomb Groups, these groups having a total of 375 aircraft on strength. A further 137 aircraft served with training and operational conversion units. This constituted the entire strategic striking force of the USAAF. With the decision to send U.S. forces to Russia in the early months of 1943, the first element to be sent was the 305th Bomb Group commanded by Colonel Curtis LeMay. The 305th arrived in Russia in June 1943 and made its appearance with a series of strikes at railheads and supply depots supporting the German advance on Kazan. The firepower of the B-17s came as an ugly surprise to the Germans and the raids, limited in depth though they were, inflicted severe damage on the German logistics infrastructure. The B-17s conducted these raids surrounded by a cloud of Russian and American escort fighters and, as a result, casualties were relatively low. This didn't remain the case however.

As 1942 turned into 1943, the American strategic bomber force in Russia expanded to include the 19th and 306th Bomb Groups, the whole force being commanded by Brigadier General LeMay. The B-17s were now escorted by American Thunderbolt fighters but the Germans were getting the measure of the Flying Fortress and losses were climbing steadily. It was conceded that the limited number of aircraft available made deep penetration raids impossible and that these would have to wait until the arrival of the B-29. In the Zone of the Interior, the 2nd and 7th Bomb Groups were already converting to the early B-29s so their aircraft were sent to replace losses in Russia. Nevertheless, by mid-1944, there were insufficient B-17s left operational to keep the B-17 groups running and the 305th and 306th Groups were sent back to the U.S.A., both to be re-equipped as B-36 groups. The 19th Bomb Group flew its last mission as a B-17 outfit in June 1944 before it was replaced in Russia by a B-29 group.


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