The B-47's development started during 1944 when the War Department's demand for jet bombers came alive. This aircraft faced many competitions including from the B-45, B-54 and the B-46. Undoubtedly, the B-47 left all others behind.
Research and development of the B-47 began in 1945 with the first prototype flight in December 1947. The Air Force’s requirements were a high-altitude, medium-range, subsonic bomber. Four manufacturers tried to meet the demand. Two of these manufacturers came up with conventional bombers in the mold of the B-29. The Northrop and the Boeing on the other hand came up with radical designs. With the massive speed and maneuverability, Boeing's swept-wing XB-47 won the bomber competition and swiftly transformed the XB-46 and the XB-48 into aviation footnotes. A total of 2,039 B-47's were built in a serial production that lasted until 1956.
Very few aircraft programs went through with as much development, production, and postproduction turbulence as the B-47 did. It was heavier than the heaviest World War II bomber. In 1947, Boeing, the manufacturer complained that the USAF had laid additional requirements that changed the concept of the overall program. In addition, the secrecy the authority maintained in developing the atomic weapons increased the difficulty of preparing the B-47 to handle the new types of special weapons.
The Army Air Force (later USAF) bought 2,000 production models of B-47 which remained in the operational inventory for nearly two decades. In comparison to the B-45, and other concurrent proposals, the B-47 had radically innovative features; the foremost being the thin swept wings which was coupled with six externally mounted jet engines. The B-47 was truly a high speed bomber, capable of carrying out effective operations despite an enemy's fighter air defense. The B-47 was the first USAF bomber to receive a weapon system designation.
When the B-47 faced challenges from B-50s and B-54s, the Truman Administration's strict monetary boundaries worked in favor of the B-47. Due to this monetary restriction, the Air Force decided to purchase more B-47s instead of B-50s and future B-54s; since none of those expensive bombers had growth potentials. Hence, the initial production order of 1948 was increased in mid 1949; even though, the first B-47 was yet to fly. The B-47 was designed to be a medium-range penetrator with approximately a 3,500-nm range; keeping in mind that in the early 1950's, forward basing was available in the UK, Spain, Morocco, Guam, and Alaska. Also, the B-47 was equipped with an air refueling capability. On most of the occasions, the B-47s were flown on 36-hour missions.
The Korean War and rising world tensions mounted urgency to develop an atomic deterrent force; which as a chain affect, raised the tempo of the B-47 program. In December 1950, the Air Force ordered a monthly production of 150 B-47s, but recommended some changes; Boeing did not like the recommendations but went with it. Six Allison J35-2 turbojet engines of the B-47 tossed in pods under the swept-back wings. It gave the bomber a agile performance. Upgraded J47-GE-3s soon substituted J35-2. The B-47 also carried mountings for 18 solid-fuel booster rockets in the aft fuselage to shorten the takeoff area.
B-47's entered the USAF inventory in 1952. ICBMs and SLBMs did not exist by than and the penetrating bomber was the only ‘nuclear strike aircraft’ available.
In 1951, the Air Force took delivery of 204 B-47Bs. Unfortunately none of them were suitable for combat operations as its canopy was unsafe; had no ejection seats; the bombing and navigation system was unreliable; a new tail defense system was needed; and the jet engines created unique development problems such as fuel boil off at high altitudes, which reduced the aircraft's range already shorter than anticipated. Additional problems included its airframe, which was built without adequate consideration for many crucial components. Also, the components, furnished by the government were behind schedule and when reached the manufacturer, did not match the sophistication of the high performance B-47. Yet, once all the problems were worked on by the engineers, B-47 proved its effectiveness.
B-47s were deployed overseas in mid 1953. By the end of 1955, B-47s totally replaced the atomic carrier B-50s. It also proved that it is capable for low altitude bombings; even though, the US made some modifications on B-47 and in 1957, publicly demonstrated its new low-altitude, strategic bombing tactics. The aircraft's payload capacity was limited to 20,000 pounds. The B-47 was also capable of carrying 13,500 pound conventional bombs.
The B-47 was used on several occasions as a test aircraft for missile launches.
In later years, when B and E series came along, there were many production improvements into it. For instance, more powerful engines with water injection were included, tail guns, ejection seats were added, maximum gross weight was increased and bomb bay modifications were incorporated for holding new weapons technology.
The B-47, in the mid 1950’s again went through numerous modifications. The most significant was the structural revision to convert the B-47 from a high to a low altitude penetrator after development of Soviet SAMs. Besides this, ECM and other avionics were also updated. Some of the B-47 aircrafts were modified into reconnaissance as well. Since space was a limitation in those aircrafts, most of them were not capable of carrying bombs. However, the engineers managed to design the RB-47B in such a way, that it could be converted back to a bomber, if necessary.
The B-47 was designed in such a way; weapons release at the target was intended to take place from high altitudes. At the target, the aircraft was to execute an Immelmann turn with weapons release taking place in near vertical flight (A change of 180° in direction coupled with a gain in altitude are accomplished during the maneuver). This method of weapons release was known as low altitude bombing system- LABS; and was intended to provide the aircraft a means for evasion from the blast effects of its own weapon release. Frequent practice of the LABS technique made the B-47 fleet to the harsh gust-load environment of high-speed low-altitude flight, as well as the maneuver loads associated with weapons release. But as the aircraft was not designed for this type of services; structural fatigue problems were reported, and several aircrafts were lost. At this stage, the entire B-47 flee was grounded for inspection and amalgamation of necessary design alterations. This fatigue problem and the much greater capability of the Boeing B-52, that entered the inventory in 1955, pushed the retirement of the B-47 from first-line service. The phase out accelerated with the rapid build up of ICBM and SLBM deployment by the US Army. Moreover, forward basing of strategic nuclear forces become detested with US allies, and there was not enough tanker support to make up the range difference for CONUS basing of all the B-47's.
As far as the numbers are concern, SAC had 8 B-47 Medium Bomber Wings in December 1953; 17 fully-equipped B-47 wings by a year later; and by the early 1956, a total of 22 medium bombing wings received B-47 while another 5 wings were into conversion process to the B-47. By 1956, B-47 deployment had reached its peak with 1,306 aircraft assigned to SAC. Overall, SAC had 30 Medium Bomb Wings, each with four squadrons of 15 aircraft per squadron; along with four Strategic Reconnaissance Medium Wings; one Combat Crew Training Wing and four Support Squadrons, which also flew different types of B-47s. The Air Force accepted a total of 2,041 B-47s. It comprised 2 XB-47s, 10 B-47As, 397 B-47Bs, 1 YB-47C, 1,341 B-47Es, 255 RB-47Es, and 35 RB-47Hs. All the other B-47s in the Air Force's operational inventory (WB-47Es, ETB-47E combat crew trainer, QB-47 drones) were obtained through post production reconfigurations.
The last B-47E was delivered on 18 February 1957 to the 100th Bomb Wing at Pease AFB, New Hampshire and SAC's last two B-47s went to ‘cargo space’ on February 11, 1966.
Despite a complicated start, the B-47 program at the end proved successful. It served in a variety of roles and experimental projects. Experiments included the development of sophisticated atomic weapons, such as Brass Ring and development of air refueling. The USAF planned to include B-58 as B-47’s replacement; which started entering the inventory in 1960. Also, the B-52, designed as a consequence of the B-47, proved to be an extremely capable ‘strategic’ bomber.
In a nut shell, life of the B-27 started in 1951 and ended 15 years later in 1966, in which the bomber proved its features quilt evidently.
B-47 Technical Specifications
Manufacturer:
Boeing Aircraft Company (primary), Douglas and Lockheed
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