Boeing B-47 Stratojet - History
     B-47 research and development began in 1945 with the first prototype flight in December 1947. The Air Force wanted a high-altitude, medium-range, subsonic bomber. At that time, four contractors were developing bombers. Two designs were conventional bombers in the mold of the B-29, while the more radical designs were the Northrop flying wing and the Boeing swept wing jet. In this era before the SAM, fighter aircraft were considered the main threat to bombers. World War II had shown that stripped down B-29's with near-fighter speed and a higher altitude ceiling could only be successfully intercepted from the rear.
      With the speed and maneuverability of the fighters of the late forties, Boeing's swept-wing XB-47 won the bomber competition and swiftly transformed the XB-46 and the XB-48 into aviation footnotes. Six Allison J35-2 turbojet engines slung in pods beneath the swept-back wings gave the prototype Stratojet nimble performance, and helped to validate a design concept still widely used today. Although uprated J47-GE-3s were soon substituted, the B-47 also carried mountings for 18 solid-fuel booster rockets in the aft fuselage to shorten the takeoff roll. Flight testing continued through 1951, and B-47's began entering the inventory in 1952. ICBMs and SLBMs did not yet exist, and the penetrating bomber was the only nuclear strike vehicle available. A total of 2,039 B-47's were funded and built in a serial production that lasted until 1956.
     Although heavier than the heaviest World War II bomber, the B-47 was designed to be a medium-range penetrator with approximately a 3,500-nm range. This was not a problem in the early 1950's since forward basing was available in the United Kingdom, Spain, Morocco, Guam, and Alaska. In addition, the B-47 was equipped with an air refueling capability and, on several occasions, 36-hour missions were flown. Thus, when it initially entered the inventory, its range was sufficient.
     The aircraft's payload capacity was limited to 20,000 pounds internally. Since nuclear weapons were large in the early 1950's, the bomb bay was limited to one or two of high yield. But this lack of payload capacity was compensated for by the large numbers of B-47's that were purchased (at a cost of less than $2 million per airplane) which resulted in an acceptable overall weapon delivery capacity. The B-47 was also capable of carrying 13 500-pound or 8 1,000-pound conventional bombs.52 Although no B-47 squadron was ever equipped with any type of missile, the B-47 was used on several occasions as a test aircraft for missile launches. The biggest aid to the B-47 payload was nuclear weapon technology which developed smaller weapons.
     Serial production made incorporating changes easier; the most numerous models were the B and E series. There were many production improvements made to include more powerful engines with water injection, the addition of tail guns, ejection seats, increased maximum gross weight, and bomb bay modifications for new weapons technology. Once deployed, modifications were numerous. The most significant was the structural revision to convert the B-47 from a high to a low altitude penetrator due to the development of Soviet SAMs in the mid 1950's. In May 1960, Gary Powers' U-2 was shot down by a Soviet SAM, vividly demonstrating Soviet high altitude defense capabilities.
     Besides structural modifications, ECM and other avionics were updated. Some B-47's were modified into reconnaissance and other specialized aircraft. Since space was a limitation, most aircraft modified for reconnaissance and special missions were not capable of carrying bombs. However, the RB-47B could be converted back to a bomber. The B-47 had the capability to be modified but was restricted by space limitations.
     The Air Force accepted a grand total of 2,041 B-47s (including the first 2 experimental planes and the prototype of a never-produced configuration). All other B-47s in the Air Force operational inventory, be they weather reconnaissance aircraft (WB-47Es), ETB-47E combat crew trainer, QB-47 drones, or others, were acquired through post-production reconfiguration.
    In December 1953 SAC had 8 B-47 Medium Bomber Wings, and a year later the SAC inventory counted 17 fully-equipped B-47 wings. By early 1956 a total of 22 medium bombing wings had received the B-47 while another 5 wings were undergoing conversion to the B-47. Thus, by the end of 1956, SAC had 27 combat-ready B-47 wings, with 1204 combat-ready B-47 crews assigned. By 1956, B-47 deployment had reached its peak with 1,306 aircraft assigned to SAC. In addition about 250 RB-47s were in SAC at that time. In all, SAC had 30 Bomb Wings (Medium), each with four squadrons of 15 aircraft per squadron, along with four Strategic Reconnaissance Wings (Medium), one Combat Crew Training Wing and four Support Squadrons/Post-Attack Command and Control Squadrons which also flew different types of B-47s.
     The final B-47E was delivered on 18 February 1957 to the 100th Bomb Wing at Pease AFB, New Hampshire. This was the 29th and last SAC bomb wing to be equipped with B-47s. The beginning of the phase-out of the B-47E coincided with the delivery of the last example in 1957. In 1960 there were still almost 1,100 B-47s. This dropped to about 400 in 1964. SAC's last two B-47s went to storage on February 11, 1966. A few RB-47s were retained until 1967. In March 1961 President Kennedy had requested funding to support an increase in the number of SAC aircraft on 15-minute ground alert from one-third to one-half the total force. At this time the B-47 phase-out was accelerated to provide the aircrews needed to support the higher alert rate of B-47 and B-52 bomber forces [which was attained by July 1961].
    In the strategic bombing role for which the B-47 was designed, weapons delivery at the target was originally intended to take place from high altitudes. By the mid-1950's, however, the increasing effectiveness of methods for detecting aircraft at high attitudes, as well as the growing capability of surface-to-air missiles and fighter aircraft, required the development of new methods of weapons delivery. As a means of avoiding detection by radar, penetration of enemy airspace was to take place at high speed and at an altitude of only a few hundred feet. At the target, the aircraft was to execute an Immelmann turn with weapons delivery taking place in near vertical flight. (An Immelmann turn consists of a half loop followed by a half roll from inverted to normal flight attitude at the top of the loop. A change of 180 in direction coupled with a gain in altitude are accomplished during the maneuver.) This method of weapons delivery was known as LABS (low altitude bombing system) and was intended to provide the aircraft a means for escaping destruction from the blast effects of its own weapon.
     Constant practice of the LABS technique subjected the B-47 fleet to the severe gust-load environment of high-speed low-altitude flight, as well as the maneuver loads associated with weapons delivery. The aircraft was not designed for this type of service. As a consequence structural fatigue problems were encountered, and several aircraft were lost as a result of structural failure. At one point, the entire B-47 flee was grounded for inspection and incorporation of necessary design modifications. Both the structural fatigue problem and the much greater capability of the Boeing B-52, which began entering the inventory in 1955, played a part in the retirement of the B-47 from first-line service. Its life with the Strategic Air Command began in 1951 and ended 15 years later in 1966.
     The phase out of the B-47 medium bomber coincided with the rapid build up of ICBM and SLBM deployment by the US. The B-47 had shown flexibility in adapting to a low level mission profile that was required by the introduction of SAMs. But modifications to a large fleet (especially structural modifications) cost vast sums of money. Moreover, forward basing of strategic nuclear forces was becoming unpopular 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. The B-58, planned as a replacement for the B-47, started entering the inventory in 1960. Also, the B-52, designed as an outgrowth of the B-47, was proving to be a very capable strategic bomber. Thus, the combination of mission profile changes, which limited B-47's usefulness and the emergence of a replacement medium-range bomber and a truly long-range strategic bomber, led to the retirement of the B-47's after 14 years of service.
     In summary, the B-47 was a technological innovation in bomber aircraft design with swept wings, jet engines, the ability to be air refueled, and an operational envelope equal to the fighter aircraft of the early 1950's. The Stratojet was also one of the more beautiful airplanes to grace America's skies. However, it was a medium-range bomber that had limitations on space, payload, and range. When deployed, the B-47 was adequate to perform its designed mission. While it was able to adapt to changes in the threat at significant cost, it was not able to keep up with a heightened threat and greater range requirements, thus making other available aircraft that did the job better more viable.