Early in 1953, just as the B-47 program was being revitalized, it seemed new and much bigger problems were on the way. President Eisenhower's defense and fiscal policies did affect the Air Force's development and procurement plans. In September, the 143 wing program was reduced to an interim 120 wings. As anticipated, the B-47 did not emerge from the crisis unscathed. Yet, all things considered, it fared well. Peak procurement, once expected to reach almost 2,200, was cut by 140 (Ten contracts 7 negotiated and 3 pending had projected total B-47 procurement to be 2,190. Naturally, as design prime contractor, Boeing had the major portion of the business-4 contracts versus Douglas's 1 and Lockheed's 2. The 3 companies similarly farmed out 50 percent of the B-47 parts to various subcontractors scattered throughout the country). But a further reduction of 200 aircraft, considered in October, was avoided. Instead the Air Force instituted a 20 month stretchout of production, pending full scale rolling of the B-52 lines. In contrast to the B-36 program so often on the verge of collapse no significant attempt was ever made to cancel the B-47 production.
The production improvement, achieved with the B-47B in 1953, did not falter. Once underway, B-47E deliveries stayed on schedule. By December, SAC had 8 B-47 Medium Bomb Wings; 1 other wing was partially equipped; 5 more had no B-47s assigned, but were scheduled to receive the new aircraft. In December 1954 (The 3 contractors achieved monthly peak production in 1954 Boeing rolled out 29 planes in September; Douglas, 11 in March, and Lockheed, 13 in May), three months after total retirement of the B-29 bombers, the inventory counted 17 fully equipped B-47 wings. Marking the beginning of an all jet medium bomb force in SAC, the last propeller driven bombers (B-50s of the 97th Wing) were phased out in July 1955. Six months later, 22 medium bomb wings had received their B-47 contingents, and another 5 wings were getting ready for the new bombers. Conversion of the SAC forces did not necessarily mean that the B-47s were totally free of problems. Nevertheless, it only took until December 1956 for SAC to accumulate 27 combat ready B-47 wings, a phenomenonal increase from 12 wings in July of the same year (In December SAC had 1,204 combat ready B-47 crews and 1,306 B-47 aircraft assigned).
In addition to materiel failures and component shortages, training problems limited the combat readiness of SAC's B-47 wings. Some argued that the B-47-be it the earliest B-47A or the latest B-47E was not inherently hard to fly. Others more realistically emphasized that the flying techniques for the new jet aircraft differed vastly from those for conventional bombers. By 1954, the B-47 had the lowest major accident rate per 100,000 flying hours of any jet aircraft. Still, 55 percent of the B-47 accidents were traced to human error, 43 percent to pilots, and 12 percent to maintenance crews. First, the size of the crew was unusually small for this type of aircraft-3 men performing the functions of pilot, copilot/gunner, and bombardier/navigator. And although the 10 or 12 crewmembers of a B-29 worked with 130 instruments, the B-47's 3 man crew confronted more than 300 gauges, dials, switches, levers, and the like. Moreover, as a true expert noted, the B-47 was relatively difficult to land and terribly unforgiving of mistakes or inattention. Although often admired, respected, cursed, or even feared, the B-47 was almost never loved (These observations were made in 1975 by Brig. Gen. Earl C. Peck, Chief of the Office of Air Force History. He knew the B-47 well, having achieved the unusual tour de force of saving his B-47 on take off despite the crucial loss of one of the plane's 6 engines. Promoted to 2 star rank in 1976, General Peck became SAC's Deputy Chief of Staff for Operations in April 1977). Even so, training progressed. In June 1954, Boeing indoctrination teams began keeping crews up to date on the B-47's limitations and stresses, and teaching techniques that would assure maximum performance under safe conditions. This new program was received with such enthusiasm that it was promptly expanded.
About the time the much improved heavyweight B-47E IV entered the inventory, more requirements were levied on the aircraft. Early in 1955 (The year started auspiciously. The B-47E IV was available, and the first B-47 for thermonuclear weapons had been delivered in January. Although the production line modification of the aircraft had been made without awaiting the results of a concurrent flight test, the Air Force was not overly concerned. Most of the essential equipment had been installed on the aircraft, and only minor changes would be needed to ready it for combat. Justifying the Air Force's confidence, more than 1,100 B-47s could handle the new thermonuclear bombs by the end of April 1956), after initial escape maneuver tests had convinced SAC that the B-47 might be rugged enough for low level bombing, the command requested a further immediate check. There were many potential benefits. High speed B-47s, flying at low level, would be less vulnerable, more difficult for enemy radars to track and less likely to be intercepted by fighter aircraft, ground fire, or surface to air missiles. Increasingly sophisticated enemy defenses would be double tasked, facing both high and low level attacks. The Air Staff swiftly endorsed SAC's request, but testing came to an abrupt halt after the loss of a low flying B-47 over Bermuda. Low level flight tests were not resumed until Boeing and the Air Research and Development Command assured Air Proving Ground Command that the B-47's structural integrity was not in doubt. In June a 6,000 pound dummy bomb was successfully released during a 2.6G pullup from level flight, and an 8,850 pound practice bomb was properly dropped from a 2.5G pullup in another flight. In both instances, release took place during the early portion of an Immelmann turn and the low altitude bombing system functioned respectably (Development of the low altitude bombing system dated back to 1952, and the low level bombing tactic was not new. SAC's fighter bomber pilots had been trained to fly at low level and the command's F-84s had been modified for this purpose. But this did not really create a precedent. One could hardly compare the 200,000 pound (design loaded weight) B-47 with aircraft of the F-84 type. The B-47's thin wings covered a span of more than 116 feet. Empty, the B-47E weighed almost 80,000 pounds. In contrast, the F-84 had a wing span of about 36 feet and its empty weight was under 12,000 pounds). In December 1955, SAC asked that 150 B-47s be modified by Boeing for low level flight. This was authorized in May 1956 . At the time, however, the Air Staff reserved approval of the same modification for other B-47s, even though SAC pointed out that AMC might do the work as part of the aircraft's IRAN program.
One year later, the Air Force made public its revolutionary strategic bombing tactic. Use of the B-47 for "toss bombing" was revealed at Eglin AFB in May 1957, during aerial firepower demonstrations before a joint civilian orientation getup. (In a toss bombing attack, the plane entered the run at low altitude, pulled up sharply into a half loop with a half roll on top, and released the weapon at a predetermined point in the climb. The bomb continued upward in a high arc, falling on the target at a considerable distance from its point of release. Meanwhile, the maneuver allowed the airplane to reverse its direction and gave it more time to speed away from the target.)
The B-47's low level flying task entailed special training requirements. These had been anticipated by SAC in Hairclipper, a training program begun in December 1955. Adverse weather, excessive maintenance requirements due to low level flying, and personnel losses to other training programs combined to hamper progress. Unexpected and serious LABS deficiencies in the low altitude bombing systems, as well as several accidents in December 1957, were the final blows. General Power, SAC's Commander in Chief since 1 July 1957, officially discontinued Hairclipper on 5 March 1958. Yet, demise of the training program did not signify the end of low level flying. Pop-Up, a related training program that took advantage of concurrent advances in weapons developments, fared better (The Pop Up tactic also put much less stress on the B-47's flexible wings than low altitude toss bombing. In the Pop Up maneuver, the aircraft swept in at low level, pulled up to high altitude, released its weapon, then dove steeply to escape enemy radars). Interrupted in April 1958, when fatigue cracks in the wing structure of some B-47s led to severe flying restrictions, Pop-up resumed in September after the aircraft had been thoroughly checked. Going strong in 1959, this program had practically reached its training goal by year's end.
The discovery of fatigue cracks in the B-47's wings and a rash of new flying accidents in early 1958 triggered an immense inspection and repair program. Nicknamed Milk Bottle and started in May 1958, the program involved all 3 manufacturers, although AMC manpower and facilities carried the largest load. More likely to suffer fatigue because of extensive low level flying training, B-47s of the 306th and 22d Bomb Wings were the first to enter the Milk Bottle program receiving an interim fix in advance of the permanent repair being devised by Boeing. The interim fix called for a major inspection of suspect areas. After dissassembly to reveal the affected structures, each bolt hole was reamed oversized. A boroscope and dye penetrant were used to locate possible cracks. If any were found, the holes were reamed again. The same kind of procedure was used on the milk bottle fittings. B-47s with no further problems-457 of them were returned to service after receiving the interim fix, which generally required about 1,700 manhours per bomber. Optimistically, as it turned out, Boeing estimated these planes would last about 400 hours before requiring further modifications. The so called "ultimate" or permanent Milk Bottle repairs were far more involved, leading to no less than 9 technical orders. Briefly stated, the repairs covered primarily the splice that joined outer and inner wing panels; the area where the lower wing skin met the fuselage and, finally, the milk bottle pin (for which the program was named) and surrounding forging located on the forward part of the fuselage, near the navigator's escape hatch. The entire endeavor proved time consuming as well as expensive-fund obligations reaching $15 million by mid year. But there were results. By the end of July, 1,230 B-47s had been through Milk Bottle, and 895 of them had already been returned to operational units. Considering its magnitude, Milk Bottle proceeded remarkably well, with most of the fleet modified by October. When the program ended in June 1959, only a few of the interim repaired aircraft still needed work, which could be done during the regular inspect and repair as necessary cycle. While Milk Bottle did not solve all problems, it put safety back into the workhorse B-47, an aircraft badly needed at the time.
The engineering fixes devised by Boeing for Milk Bottle showed that it was possible to identify the parts in an aircraft that were most likely to fail, but left many questions unanswered. No one could explain why primary structures in the B-47 were affected by maneuvers that the aircraft was designed to perform. General Power saw no use in turning to other aircraft unless SAC was assured they would survive low level flying. General Power insisted that despite Boeing's evaluation of the B-47's structural life since 1956, not enough was known about aircraft service span. General LeMay agreed that weapon system producers had to give the Air Force more information on operation and its effect on metal fatigue. In addition, the Air Force and aircraft industry needed to combine their efforts. They had to expand existing programs to collect statistical maneuver loads data, to conduct cyclic testing, and to develop better instrumentation and analytical techniques (Wright Air Development Center was already considering the B-47's fatigue problem in May 1958 and was flight testing a Douglas B-66 light bomber to learn more about low altitude turbulence. Moreover, closely related projects were either in being or soon to start). The knowledge to be gained, General LeMay thought, together with judicious application of engineering skills and maintenance funds would prevent the early retirement of aircraft, an extremely expensive alternative (Some 15 years later, low flying B-52s continued to attest to the concept's value.). Yet, in any aircraft's life cycle, there was a point beyond which further repair became uneconomical. Perhaps, General LeMay noted, all that could be done to keep the aged B-47 combat ready was to correct anticipated problems.
Devising the Milk Bottle repairs was just a beginning. While the repairs were underway, Boeing had to develop a broad structural integrity program to determine the modification's impact on the B-47's service life. Moreover, any other potential problem areas had to be uncovered. The collapse of Boeing's cyclic test aircraft in August 1958 revealed for instance that the B-47's upper longerons the beams running lengthwise along the fuselage were susceptible to fatigue when the aircraft approached 2,000 hours of flying time (This led to further inspections, the identification of 11 B-47s with defective longerons, and the Air Material Command's eventual modification of all the aircrafts' support beams). Similar cyclic tests by Douglas and the National Aeronautics and Space Administration (NASA) did not disclose any serious deficiency until December, when NASA ceased testing after a fracture appeared near one of the B-47's wing stations. Boeing tests continued until January 1959, without duplicating NASA's discovery. But when Douglas stopped in February, after almost 10,000 test hours, its B-47 had also developed a 20 inch crack. If the cyclic testing of the late fifties truly simulated flight conditions, NASA and Douglas's findings were relatively important, since SAC's B-47s had never been individually tagged for 10,000 flying hours. In any event, there were gaps in other crucial research. The low altitude flying program, using oscillograph recorders to track the stresses and strains of lower levels on the B-47, was far from complete. Still a decision had to be made without delay, if only to justify the purchase of other aircraft. In mid 1959, the Air Force cautiously assigned the B-47 a life expectancy of 3,300 hours. Implied was the requirement for regular rigid inspections. In addition, the Wright Air Development Center admitted that this figure was based on technical consideration only. It could change, because service life did not reflect economic or operational factors.
SAC initially wanted 1,000 B-47s modified for low-level flying. This meant fitting the aircraft with absolute altimeters, terrain clearance devices (The kind SAC needed to fly low at night or during periods of reduced visibility did not even exist in 1956), and doppler radars the type of new equipment that would require extensive testing and lots of money. In 1959, it became evident that the B-47 would survive the Milk Bottle crisis only to face other severe problems. Because of development testing slippages and the money saving phaseout of some B-47 wings, SAC scaled down its low altitude requirements by half. The command did stress, however, the urgency of modifying the 500 B-47s now earmarked for low level flying. SAC again pointed out that the aircraft lacked missile penetration aids and was marginally suited for high altitude strikes. Against improved enemy defenses, the B-47 would be obsolete in 1963 if not properly equipped for low level flight. The Air Staff did not question SAC's justifications, but fund shortages dictated harsh decisions. Hence, in lieu of 500, only 350 B-47s would be modified for low level flying, and the aircraft would receive simpler and much less costly equipment than asked for by SAC (The Air Force had canceled in late 1958 the B-47's use of the GAM 72 Quay, a short range decoy missile, mainly because of dollar limitations. Procurement of the GAM 67 Crossbow had already been dropped, and modification of the B-47 to protect it from infrared missiles was abandoned in mid 1959). Obviously, the end of the B-47 was in sight.
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