The first large-scale production version of the Stratofortress was the B-52D (Model 464-201-7), of which 170 were built between June 1956 and November 1957. The B-52D was externally indistinguishable from the B-52C which preceded it. The only significant internal difference was the adoption of the MD-9 fire control system as fitted to the final B-52C. The powerplants were the J57-P-19W or -29W. In contrast to the B-52C, which was readily convertible to the reconnaissance configuration, the B-52D was built exclusively for the long-range bombing role and could not accommodate the bomb-bay mounted reconnaissance and observation pod.
The B-52D was the first Stratofortress to be built at two different locations. 69 examples were built at Boeing's Wichita, Kansas facility, with the remainer being built in the main Boeing plant in Seattle. The Wichita plant had originally been owned by the Stearman Aircraft Company but had been acquired by Boeing in 1934 and became a Boeing division in 1939. It had been used during World War 2 as an inland site for B-29 manufacture. The decision to shift B-52 production from Seattle to Wichita was a result of several factors. The commercial business at Seattle was picking up and Boeing needed more plant space to handle the orders. It so happened that there was a large, well-qualified work force already at hand in Wichita which was working on the B-47, the production of which was winding down.
The first contract for Wichita-built B-52D aircraft was AF33(600)-26235, which was concluded on November 29, 1954. Two serial number batches were assigned to these planes--55-0049/0067 and 55-0673/0680. A second contract, AF33(600)-31155, finalized on January 31, 1956, covered 42 more Wichita-built B-52Ds. Serials were 56-06567/0698.
An initial batch of 50 Seattle-built B-52Ds was ordered by contract AF33(600)-28223, which was finalized on August 31, 1954. Serials were 55-0068/0117. AF33(600)-31267 signed on October 26, 1955 covered 51 more Seattle-built B-52Ds. Serials were 65-0580/0630.
Seattle and Wichita used completely different schemes for their company serial numbers. Wichita's first B-52 bore the company number of 464001, where 464 stood for the model number and 001 meant that it was the first B-52 example coming off the production line. Seattle's B-52s c/n started with 16248 for the XB-52 and ended with 17467. The difference is greater than the total number of 277 B-52s built at Seattle due to other Boeing models such as the KC-135 being built concurrently at Seattle.
It was a Wichita-built aircraft which was the first B-52D to fly, on May 14, 1956. The first Seattle-built B-52D took off on its initial flight on September 28, 1956. The first B-52Ds reached SAC in the fall of 1956. The first few went to the 42nd Bombardment wing at Loring AFB, replacing the wing's initial B-52Cs. By the end of December 1956, several B-52Ds had been delivered to the 93rd Bombardment Wing.
There were problems with fuel leaks, with icing of the fuel system, and with malfunctions of the water injection pumps. The problem with the water injection pumps was eventually traced to the fact that the pumps would still keep operating even after the water tanks were empty. Installation of water sensors was the answer.
In 1959, SAC was faced with the growing capability of Soviet air defenses, and it was concluded that high-altitude operations with the B-52 would be increasingly hazardous in the future. The answer was to switch to low-altitude operations, where the B-52 would be much harder to detect and where Soviet defenses were known to be far less reliable. Although the B-52 was originally designed for high-altitude operations, all B-52s except for the early B-52Bs would now have to be capable of penetrating enemy defenses at altitudes as low as 500 feet. These low altitude B-52Ds were to be fitted with the ability to carry Hound Dog cruise missiles and Quail decoys, originally to have been carried only by the B-52G and H.
At first sight, the low-level modifications to the B-52D appeared to be fairly straightforward, including the improvement of the aircraft's bombing/navigation system, modification of the Doppler radar, and the addition of a terrain clearance radar. Low-altitude altimeters had to be acquired. The project rapidly became more complicated, since different B-52 models had to be accommodated. Airframes had to be strengthened, and the low-level structural modifications required for each B-52C and D were almost twice as costly as those that were required for any other B-52. The development of special terrain clearance radars proved more difficult than expected.
An AN/ALQ-27 electronic countermeasures system was to be fitted, which would, it was hoped, allow the B-52 to counter Soviet missiles and airborne fire control systems as well as early warning and ground control interception radars. However, the AN/ALQ-27 system was cancelled as being too complex and costly. In its place was a Quick Reaction Capability (QRC) package that was installed in new-build B-52Hs and retrofitted to earlier versions. The program was known as Big Four or "Mod 1000", and was carried out between November 1959 and September 1963.
The ECM improvements were to take place in several phases. Phase I was an emergency modification that provided the necessary minimum ECM equipment to counter the Soviet radar and surface-to-air missile threat. Phase II was essentially an ECM retrofit that was included in the Big Four package. The best available ECM equipment, comparing favorably to the cancelled AN/ALQ-27 system, was installed in Phase III.
As part of the switch from high-level to low-level missions, a lot of structural fixes had to carried out in order to prevent fatigue cracks from resulting in catastrophic failures. The first phase took place as each aircraft reached its 2000 flying hour mark and involved strengthening of the fuselage bulkhead and aileron bay plus reinforcement of boost pump panels and wing foot splice plates. Phase II was invoked when the aircraft reached its 2500 hour mark and involved repairs and reinforcements to upper wing splices inboard of the inner engin pods, lower wing panels supporting inner and outer engine pods, upper wing surface fuel probe access doors and the lower portion of the fuselage bulkhead. Phase III was an IRAN (Inspect and Repair As Necessary) project that dealt with wing cracks.
Less than 6 months after the B-52F became involved in combat in Vietnam, the Air Force decided to convert most of its B-52Ds to conventional warfare capability for service in Southeast Asia. Foremost among the changes needed was to give the B-52D the ability to carry a significantly larger load of conventional bombs. This led to the Big Belly project which was begun in December of 1965. The project increased the internal bomb capacity from just 27 weapons to a maximum of 84 500-lb Mk 82 or 42 750 lb M117 conventional bombs. This was done by careful rearrangement of internal equipment, and did not change the outside of the aircraft. In addition, a further 24 bombs of either type could be carried on modified underwing bomb racks (originally designed for the carrying of Hound Dog cruise missiles and fitted with I-beam rack adapters and a pair of multiple ejection racks), bringing the maximum payload to 60,000 pounds of bombs, about 22,000 pounds more than the capacity of the B-52F.
During 1967-1969, the B-52Ds assigned to conventional warfare missions in Southeast Asia were given a set of electronic warfare updates. This was done under a program known as Rivet Rambler or Phase V ECM fit. This involved the fitting of one AN/ALR-18 automated set-on receiving set, one AN/ALR-20 panoramic receiver set, one AN/APR-25 radar homing and warning system, four AN/ALT-6B or AN/ALT-22 continuous wave jamming transmitters, two AN/ALT-16 barrage-jamming systems, two AN/ALT-32H and one AN/ALT-32L high- and low-band jamming sets, six AN/ALE-20 flare dispensers (96 flares) and eight AN/ALE-24 chaff dispensers (1125 bundles).
Camouflage paint in tan and two shades of green, still with white undersides, was applied to B-52s in 1965, at the same time when other USAF aircraft were adopting camouflage. B-52Ds assigned to combat duty in Vietnam were painted in a modified camouflage scheme, with the undersides, lower fuselage, and both sides of the vertical fin being painted in a glossy black. The USAF serial number was painted in red on the fin.
55-0049/0051 Boeing B-52D-1-BW Stratofortress c/n 464001/464003 55-0052/0054 Boeing B-52D-5-BW Stratofortress c/n 464004/046006 55-0055/0060 Boeing B-52D-10-BW Stratofortress c/n 464007/464012 55-0061/0064 Boeing B-52D-15-BW Stratofortress c/n 464013/464016 55-0065/0067 Boeing B-52D-20-BW Stratofortress c/n 464017/464019 55-0068/0088 Boeing B-52D-55-BO Stratofortress c/n 17184/17204 55-0089/0104 Boeing B-52D-60-BO Stratofortress c/n 17205/17220 55-0105/0117 Boeing B-52D-65-BO Stratofortress c/n 17221/17233 55-0673/0675 Boeing B-52D-20-BW Stratofortress c/n 464020/464022 55-0676/0680 Boeing B-52D-25-BW Stratofortress c/n 464023/464027 56-0580/0590 Boeing B-52D-70-BO Stratofortress c/n 17263/17273 56-0591/0610 Boeing B-52D-75-BO Stratofortress c/n 17274/17293 56-0611/0630 Boeing B-52D-80-BO Stratofortress c/n 17294/17313 56-0657/0668 Boeing B-52D-30-BW Stratofortress c/n 464028/464039 56-0669/0680 Boeing B-52D-35-BW Stratofortress c/n 464040/464051 56-0681/0698 Boeing B-52D-40-BW Stratofortress c/n 464052/464069