The Boeing Model 450 B-47
Stratojet was a long-range, six-engine, jet-powered medium
bomber built to fly at high subsonic speeds and at high
altitudes. It was primarily designed to drop nuclear bombs on
Soviet Union. With its engines carried in pods under the
swept wing, the B-47 was a major innovation in post-World
War II combat jet design, and helped lead to modern
The B-47 entered service with the
United States Air Force's
Strategic Air Command (SAC) in 1951. It never saw combat as
a bomber, but was a mainstay of SAC's bomber strength during the
1950s and early 1960s, and remained in use as a bomber until
1965. It was also adapted to a number of other missions,
including photo reconnaissance,
electronic intelligence and weather reconnaissance,
remaining in service as a reconnaissance platform until 1969 and
as a test bed until 1977.
The B-47 arose from a informal 1943
requirement for a
jet-powered reconnaissance bomber, drawn up by the
U.S. Army Air Forces (USAAF) to prompt manufacturers to
start research into jet bombers. Boeing was among several
companies that responded to this request; its initial design,
the Model 424, was basically a scaled-down version of the
Boeing B-29 Superfortress equipped with four jet engines.
The next year, this concept evolved into a formal
request-for-proposal to design a new bomber with a maximum speed
of 550 mph (800 km/h), a cruise speed of 450 mph (725 km/h), a
range of 3,500 mi (5,600 km) and a service ceiling of 45,000 ft
North American Aviation, the
Boeing and the
Glenn Martin Company submitted proposals for the new
long-range jet bomber in December 1944. Wind tunnel testing had
shown that the drag from the engine installation of the Model
432 was too high, so Boeing engineers then tried a revised
design, the Model 432, with the four engines buried in the
forward fuselage. The USAAF awarded study contracts to all four
companies, requiring that North American and Martin concentrate
on four-engine designs, (to become
North American B-45 and
Martin XB-48), while Boeing and Convair were to build
six-engine aircraft (the B-47 and
B-46). The power plant was to be
General Electric's new
In mid-1945, with the defeat of
Germany immanent, the
von Kármán mission of the Army Air Forces inspected German
aeronautics laboratories from the beginning of May through
the end of July 1945, in search of German developments that
might help the United States. One of the Boeing engineers on the
mission, George Schairer, studied German reports on the effects
wing sweepback on the performance of aircraft as they
approached the speed of sound, and realizing the possible
implications for the new bomber, sent word back to Boeing to
stop work on the straight-winged design and switch to swept
Analysis work by the Boeing
engineer Vic Ganzer suggested an optimum sweepback angle of
about 35 degrees. Boeing's aeronautical engineers modified their
Model 432 design to include swept wings and
tail, resulting in the "Model 448", which was presented to
the USAAF in September 1945. The Model 448 retained its four
TG-180 jet engines in its forward fuselage, with two more
TG-180s in the rear fuselage. The flush-mounted air intakes for
the rear engines were inadequate, while the USAAF disliked the
installation of engines within the fuselage, considering it a
The engines were moved out to
streamlined pods pylon mounted under the wings, leading to the
next iteration, the Model 450, which featured two TG-180s
in a twin pod mounted on a pylon about a third of the way
outboard on each wing, plus another engine at each wingtip. The
Army Air Force liked this new configuration, and so Boeing's
team of engineers continued to refine it, with the outer engines
being moved further inboard, to about 3/4 of the
wingspan. The thin wings provided no room into which wheels
could be retracted, so a "bicycle landing gear" was chosen, with
the two main gear assemblies arranged in a tandem configuration
and outrigger struts fitted to the inboard engine pods. As the
landing gear arrangement made
rotation (i.e. lifting the nose during take-off) impossible,
the landing gear was designed so that the aircraft rested on the
ground at the proper angle for take-off.
The USAAF was very pleased with the
refined Model 450 design, and in April 1946, the service ordered
two prototypes, to be designated "XB-47". Assembly began in June
1947. People involved with the project were very excited, since
they believed (correctly as it turned out) they were working on
a breakthrough in aircraft design.
The first XB-47 was rolled out on 12
September 1947, a few days before the USAAF became a separate
U.S. Air Force on 18 September 1947. The XB-47 prototype
flew its first flight on 17 December 1947 (the anniversary of
Wright Brothers' first four flights on December 17, 1903),
with the test pilots Robert Robbins and Scott Osler at the
controls of the airplane. It flew from
Boeing Field in
Seattle to the
Moses Lake Airfield in central
Washington state, in a flight that lasted just 27 minutes,
with no major problems. Robbins had to pull up the flaps with
the emergency hydraulic system, and the "engine fire"
warning lights kept lighting up. Robbins reported that the
flight characteristics of the aircraft were good.
The XB-47, which looked unlike any
contemporary bomber, was described by some observers as a
"sleek, beautiful outcome that was highly advanced". The
35-degree swept wings were shoulder-mounted, with the twin
inboard turbojet engines mounted in neat pods, and the outboard
engines tacked under the wings short of the wingtips. With the
exception of a change from the shoulder-mounted wing
configuration to being under the fuselage, most future airliners
would use a similar configuration, with the engines mounted in
under wing pylons.
The airfoil was 11 times as wide as
it was thick. This unusual thinness (dry, no fuel tanks) was
believed to be necessary to attain high speed (0.86 Mach), but
the wing's flexibility was a concern. It could flex as much as
5 ft (1.5 m) up or down, and major effort was expended to ensure
that flight control could be maintained as the wing moved up and
down. As it turned out, most of the worries proved unfounded.
(Wing "twist" limited tree-top speed to 425 knots (787 km/h) to
control reversal.) The wings were fitted with a set of
Fowler flaps that extended well behind the wing, to enhance
lift at slow speeds.
Performance and Engines
The performance of the Model 450
design was projected to be so good that the bomber would be as
fast as fighters then on the drawing board, and so the only
defensive armament was to be a tail turret with two .50 in
(12.7 mm) Browning machine guns, which would in principle be
directed by an automatic fire-control system. The two XB-47s
were not fitted with the tail turret as they were engineering
and flight test aircraft; indeed, the prototypes had no combat
equipment at all.
Fuel capacity was enormous, at
17,000 gal (64,400 l), more than triple the 5,000 gal (19,000 l)
on the B-29 Superfortress. That meant that maintaining fuel trim
to ensure a stable center of gravity in flight would be a very
critical copilot duty.
The first prototypes were fitted
with General Electric
J35 turbojets, the production version of the TG-180, with
(17.7 kN) of thrust. Early jet engines did not develop good
thrust at low speeds, so to help a heavily loaded bomber take
off, the XB-47 prototype had provisions for fitting 18
rocket-assisted takeoff (RATO) rockets with 1,000 lbf (4.4 kN)
thrust each. Fittings for nine such units were built into each
side of the rear fuselage, arranged in three rows of three
A related problem was that the
aircraft's engines would have to be throttled down on landing
approach. Since it could take as long as 20 seconds to throttle
them back up to full power, the big bomber could not easily do a
"touch and go" momentary landing. A small "approach chute" was
provided for drag so that the aircraft could be flown at
approach speeds with the engines throttled at ready-to-spool-up
medium power. Training typically included an hour of dragging
this chute around the landing pattern for multiple practice
The aircraft was so aerodynamically
slick that rapid descent ("penetration") from high cruise
altitude to the landing pattern required dragging the deployed
rear landing gear.
Unusually heavy wing loading
(weight/wing area) required a high landing speed of 180 knots.
To shorten the landing roll, Air Force test pilot
Guy Townsend promoted the addition of a 32 ft (9.75 m)
German-designed "ribbon" drag chute. (Jet engine
thrust reversers were still a "far-future" concept.). As a
consequence, the B-47 was the first mass-produced aircraft to be
equipped with an anti-skid braking system.
Crew and Loads
The XB-47 was designed to carry a
crew of three in a pressurized forward compartment: a pilot and
copilot, in tandem, in a long fighter-style bubble canopy, and a
navigator in a compartment in the nose. The copilot doubled as
tail gunner, and the navigator as bombardier. The bubble canopy
could pitch up and slide backward, but as the cockpit was high
off the ground, crew entrance was through a door and ladder on
the underside of the nose.
Total bomb load capacity was to be
10,000 lb (4.5 metric tons). Production aircraft were to be
equipped with state-of-the-art electronics for navigation,
bombing, countermeasures, and turret
During early tests of the XB-47
prototype, the canopy came off at high speed, killing pilot
Scott Osler. The copilot safely landed the aircraft. This
resulted in a canopy redesign, and the hiring of pilot
The second XB-47 prototype first
took the air on 21 July 1948, and was equipped with much more
powerful General Electric
J47-GE-3 turbojets with 5,200 lbf (23 kN) thrust each. The
J47 or "TG-190" was a redesigned version of the TG-180/J35. The
first XB-47 prototype was later retrofitted with these engines.
Flight testing of the prototypes was
particularly careful and methodical, since the design was so new
in many ways. The prototypes initially suffered from "Dutch
roll", an instability that caused the aircraft to weave in
widening "S" turns. This problem was remedied by the addition of
damper" control system that applied rudder automatically to
damp out the weaving motion. The prototypes also had a tendency
to pitch up. This problem was solved by adding small vanes
generators" onto the wings that caused turbulence to prevent
Boeing test pilot Rob Robbins had
originally been skeptical about the XB-47, saying that before
the initial flight he had "prayed to God to please help me"
through the flight. The aircraft was so unusual that he simply
didn't know if it would fly. Robbins soon realized that he had
an extraordinary aircraft.
In early 1948, the
United States Air Force (having become a separate service in
1947) sent up a
chase plane from Muroc (now
Edwards) Air Force Base in California to help calibrate the
bomber's airspeed system. Robbins reported later:
||[The chase plane] was a
P-80 [Lockheed Shooting Star] and
Chuck Yeager was flying it. Chuck's a hell of a good
pilot, but he had a little bit of contempt for bombers
and a little disdain for civilian test pilots. Well, we
took off, climbed out, and got up somewhere within four
or five points of full throttle speed.
At that point, Chuck called me on the radio and said:
"Bob, would you do a 180?" I thought, Hey, Chuck's
smart, he just wants to stay reasonably close to Moses
Lake, he doesn't have as much fuel as I do. Well, I
turned around, got stabilized, and looked for Chuck. He
wasn't there. Finally, I got on the radio and said,
"Chuck, where are you?" He called back and rather
sheepishly said, "I can't keep up with you, Bob." So
Chuck Yeager had to admit to a civilian test pilot
flying a bomber that he couldn't keep up! That was
Yeager would test-fly the XB-47
later in its development cycle and would years later note that
the aircraft was so aerodynamically clean that he had difficulty
putting it down on the runway.
By mid-1948, the Air Force's bomber
competition had already been through one iteration, pitting the
XB-45 against the Convair
XB-46. The North American design won that round of the
competition, and as an interim measure the USAF had decided to
put the North American bomber into production on a limited basis
B-45 Tornado. The expectation was that B-45 production would
be terminated if either of the remaining two designs in the
competition, the Boeing XB-47 and the Martin
XB-48, proved superior. It is sometimes claimed that the
final production decision was made as a result of Boeing
Bill Allen inviting USAF General K.B. Wolfe, in charge of
bomber production, for a ride on the XB-47. A formal contract
for 10 aircraft was signed on 3 September 1948.
The total number of B-47s built was
Strategic Air Command operated B-47 Stratojets (B-47s,
EB-47s, RB-47s and YRB-47s) from 1951 through 1965.
When B-47s began to be delivered to
the Air Force, most crews were excited about getting their hands
on the hot new bomber, an aircraft whose performance was closer
to that of jet fighters of the period than SAC's extant
B-36 Peacemaker bomber. The B-47 was so fast that in the
early days the aircraft set records with ease. The aircraft
handled well in flight, with a fighter-like light touch to the
controls. The large
bubble canopy for the pilot and co-pilot enhanced the
fighter-like feel of the aircraft with improved vision, but the
design would also cause variations in internal temperatures for
the three-man crew.
It took the Air Force until 1953 to
turn the B-47 into an operational aircraft. The aircraft was
sluggish on takeoff and too fast on landings, a very unpleasant
combination. If the pilot landed at the wrong angle, the
aircraft would "porpoise", bouncing fore-and-aft. If the pilot
didn't lift off for another go-round, instability would quickly
cause the bomber to skid onto one wing and cartwheel. Because
the wings and surfaces were flexible and bent in flight, low
altitude speed restrictions were necessary to ensure effective
Improved training led to a good
safety record, and few crews felt the aircraft was unsafe or too
demanding, but apparently there were some aircrews who had
little affection for the B-47. Crew workload was high, with only
three officer crew members to keep the B-47 flying right. The
B-52 Stratofortress, in contrast, generally had six crewmen,
5 officers and 1 enlisted, with far more internal cabin space.
The B-47's reliability and
serviceability were regarded as good. The only major problem was
poor avionics reliability, normal in this environment given the
vacuum tube technology at the time, and the need to place
some equipment outside the pressurized crew compartment. Much
work was done to improve avionics reliability, but they remained
problematic throughout the B-47's operational life.
Several models of the B-47 starting
in 1950 included a fuel tank
inerting system, in which
dry ice was sublimated into
carbon dioxide vapor while the fuel pumps operated or while
the in-flight refueling system was in use. The carbon dioxide
was then pumped into the fuel tanks and the rest of the fuel
system, ensuring that the amount of oxygen in the fuel system
was low, and thereby reducing the probability of an explosion.
Ten carbon dioxide tanks and heaters were involved. The system
was implemented largely to reduce risks from
static electricity discharges occurring during in-flight
Initial mission profiles included
loft bombing (Low Altitude Bombing System) of nuclear
weapons. As the training for this imposes repeated high stress
on the aircraft, the airframe lifetime would have been severely
metal fatigue, and this maneuver was eliminated.
By 1956, the U.S. Air Force had 28
wings of B-47 bombers and five wings of RB-47 reconnaissance
aircraft. The bombers were the first line of America's strategic
nuclear deterrent, often operating from forward bases in the
Alaska, Greenland and
B-47 bombers were often set up on "one-third" alert, with a
third of the operational aircraft available sitting on
hardstands or an alert ramp adjacent to the runway, loaded with
fuel and nuclear weapons, crews on standby, ready to attack the
USSR at short notice.
Crews were also trained to perform
"minimum interval takeoffs (MITO)", with one bomber following
the other into the air at intervals of as little as 15 seconds,
to launch all bombers as fast as possible. MITO could be
hazardous, as the bombers left turbulence and, with first
generation turbojet engines with water injection systems, dense
black smoke that blinded pilots in the following aircraft.
B-47 bombers apparently performed
training missions in which they penetrated Soviet airspace in
The B-47 would be the backbone of
SAC into 1959, when the B-52 began to assume nuclear alert
duties and the number of B-47 bomber wings started to be
reduced. B-47 production ceased in 1957, though modifications
and rebuilds continued after that.
Operational practice for B-47 bomber
operations during this time went from high altitude bombing to
low altitude strike, which was judged more likely to penetrate
Soviet defenses. Bomber crews were trained in "pop-up" attacks,
coming in at low level at 425 knots (787 km/h) and then climbing
abruptly near the target before releasing a nuclear weapon, and
the similar "toss bombing" procedure, in which the aircraft
released the weapon while climbing, and then rolled away to
depart the area before bomb detonation.
Stress and fatigue incurred in
low-altitude operations led to a number of wing failures and
crashes and an extensive refit program was begun in 1958 to
strengthen the wing mountings. The program was known as "Milk
Bottle", named after the big connecting pins that were replaced
in the wing roots.
One of the more notable mishaps
involving a B-47 occurred on 5 February 1958 near Savannah,
Georgia, in the so-called 1958 Tybee Island B-47 crash. A B-47
based out of Homestead AFB, Florida was engaged in a simulated
combat exercise with an F-86 Sabre, the bomber simulating an
attacking aircraft and the fighter a defender. As was the
practice at the time, the B-47 was carrying a single 7,600 lb
(3,400 kg) Mark 15 nuclear bomb without its core. During this
exercise, the F-86 collided with the B-47. The F-86 pilot
ejected and the fighter crashed, while the B-47 suffered
substantial damage, including loss of power on one of its
outboard jet engines. The bomber pilot had to "safe" soft drop
the Mark 15 weapon off the coast of Savannah, Georgia near Tybee
Island after three unsuccessful landing attempts at Hunter Air
Force Base. The bomb was jettisoned and the aircraft landed
safely. An extensive nine-month search was mounted for the
unarmed bomb, but proved futile.
The only B-47s to see anything that
resembled combat were the reconnaissance variants. They operated
from almost every airfield that gave them access to the USSR,
and they often probed Soviet airspace, and on occasion, B-47
pilots were caught in situations from which mostly speed and
evasion in retreat saved them. At least five of these aircraft
were fired on, and three of these were shot down. The B-47s
fired back with their tail turrets, though it is uncertain if
they scored any kills, but in any case these were the only shots
fired in anger by any B-47.
Final phase-out of B-47 bomber wings
began in 1963, and the last bombers were out of service by 1965.
The very last USAF operational aircraft was grounded in 1969.
The U.S. Navy kept specialized B-47 test aircraft in occasional
use up to 1976. The final recorded flight of a B-47 was on 17
June 1986, when a B-47E was flown from the Naval Air Weapons
Station China Lake, California, to Castle Air Force Base,
California, for static display at the Castle Air Museum.
Strategic operations of the 2,000
B-47s required 800 KC-97 Stratotankers. On a typical RB-47H
reconnaissance mission covering 5,984 mi (9,360 km), the
aircraft would fly from Thule, Greenland to the Kara Sea to
Murmansk and then return only to find Thule weathered-in,
forcing the flight from the air-refueling/decision point near
the northeast shore of Greenland to one of three equidistant
alternates: Goose Bay, Labrador, London, or Fairbanks, Alaska.
Five KC-97s at Thule were required to support this scenario. Two
ground spares and one air spare insured two 20,000 lb (9,090 kg)
fuel transfers at a distance of over 600 mi (965 km) from Thule.
Tankers returned to Thule to refuel and again repeat the flight
to intercept the returning RB-47H six hours later for another
The first over flight of Soviet
territory with an RB-47 took place on 15 October 1952, when an
RB-47B flying out of Alaska overflew Soviet airfields in Eastern
On 8 May 1954, after a top secret
reconnaissance mission in the Kola Peninsula, a 4th Air Division
91 Strategic Reconnaissance Wing RB-47E reconnaissance aircraft,
with Hal Austin at the controls, flew west from the Soviet
Union. The RB-47E was flying at high altitude, out of reach of
MiG-15s, but unknown to USAF intelligence some MiG-17s had been
stationed in the area and they were able to intercept the
intruder, so the plane was being chased by three Soviet MiG-17
jet fighters. The Soviet fighters tried to destroy the RB-47E
with their guns in Soviet and Finnish airspace, but the damaged
RB-47E managed to escape over Sweden back to RAF Fairford
station in Gloucestershire, England, where it had taken off,
thanks to its remarkable top speed and combat radius superior to
the Soviet fighter jets. It was the first mission in which a jet
airplane equipped with modern photography equipment was used by
American military reconnaissance. The incident was kept secret
by all parties.
One RB-47 flying out of Alaska was
scouting out the Kamchatka Peninsula on 17 April 1955, when it
was bounced by Soviet MiG-15s in international airspace. The
RB-47 and its crew disappeared. Between 21 March and 10 May
1956, 16 RB-47Es and 5 RB-47Hs operating from Thule performed
over flights the length of Siberia 156 times under Project HOME
RUN. The Soviets filed an angry complaint with the US
government, which attributed the over flights to "navigational
difficulties". MiGs did bounce RB-47s on three separate
occasions in the fall of 1958, with one incident over the Black
Sea on 31 October, the second over the Baltic on 7 November, and
the third over the Sea of Japan on 17 November.
On 1 July 1960, a PVO Strany MiG-19
shot down an RB-47H (AF Serial No. 53-4281) reconnaissance
aircraft in the international airspace over the Barents Sea with
four of the crew killed and two captured by the Soviets but
released in 1961. The co-pilot reported that the MiG-19 jammed (whited-out)
his MD-4 FCS scope rendering the RB-47H defenseless.
The last known confrontation between
MiGs and RB-47s took place on 27 April 1965, when an ERB-47H was
jumped by North Korean MiG-17s over the Sea of Japan. The MiGs
gave the ERB-47H a working over, but it managed to make it back
to Yokota Air Base in Japan with two engines out.
While a few of these aircraft
performed special duties during the Vietnam War, such as
relaying ELINT data from drones, they were eventually replaced
by much more comfortable and capable Boeing RC-135 platforms.
The last RB-47H was retired on 29 December 1967.
The final 15 RB-47Es built were
fitted with additional equipment, including the AN/APD "side
looking airborne radar (SLAR)" system, and gear to sample the
air for fallout from nuclear tests. The Air Force judged them
different enough on delivery, beginning in December 1955, to
give them a new designation of RB-47K.
The RB-47Ks were generally used for
weather reconnaissance missions, carrying a load of eight "dropsonde"
weather sensors that were released at various checkpoints along
the aircraft's flight path. Data radioed back from the
dropsondes was logged using equipment operated by the navigator.
The RB-47Ks stayed in service until 1963.
Incidentally, there were B-47F,
B-47G, and B-47J variants, but these were all one-shot
conversions of B-47Bs or B-47Es, to be discussed later. There
never was a B-47I variant. The Air Force never designated a
B-47I, because the "I" suffix was too easily confused with the
- Two prototype aircraft. Two built as Model 450-1-1 and
450-2-2 respectively,(46-065 and 46-066). Powered by six
Allison J-35-GE-7 turbojet engines for the first flights.
The second, and subsequent, aircraft were built with the
specified General Electric J-47-GE-3 engines, which were
retro-fitted to the first XB-47.
The first 10 aircraft were designated "B-47A", and were
strictly evaluation aircraft. The first was delivered in
December 1950. The configuration of the B-47As was close to
that of the initial XB-47 prototypes. They were fitted with
J47-GE-11 turbojets, offering the same 5,200 lbf (23 kN)
thrust as the earlier J47-GE-3, and they also featured the
built-in RATO bottles.
- Four of the B-47As were fitted with the K-2 bombing and
navigation system (BNS), with an HD-21D autopilot, an analog
computer, APS-23 radar, and a Y-4 or Y-4A bombsight. Two
were fitted with the tail turret, one of them using an
Emerson A-2 fire control system (FCS), another an early
version of the General Electric A-5 FCS. The eight other
B-47As had no defensive armament.
- The B-47As were fitted with ejection seats. The pilot
and copilot ejected upward, while the navigator had a
downward ejection seat built by Stanley Aviation. Minimum
safe ejection altitude was about 500 ft (150 m).
- While the XB-47s had been built by Boeing at their
Seattle, Washington, plant, the B-47As and all following
Boeing B-47 production were built at a government-owned
factory in Wichita, Kansas, where the company had built
B-29s in the past. The switch was made as the Seattle plant
was burdened with KC-97 Stratotanker production and other
- Most of the B-47As were phased out of service by early
1952, though one did perform flight tests for NACA for a few
more years. While the Air Force put the B-47As through their
paces, the Cold War was rising to full force, with a
hot war intensifying in Korea. The USAF's Strategic Air
Command (SAC) needed an effective nuclear deterrent to keep
the Soviet Union in line, and the Stratojet was an excellent
tool for the task, and Boeing was already working on
Following a series of preliminary contracts for production
B-47s, in November 1949, even before the first flight of the
B-47A, the Air Force had ordered 87 B-47Bs, the first
operational variant of the type. The first B-47B flew on 26
April 1951. A total of 399 were built, including eight that
were assembled by Lockheed and ten that were assembled by
Douglas, using Boeing-built parts.
- The USAF was impatient to get their hands on as many
B-47s as they could as quickly as possible, and signed up
Lockheed and Douglas for the additional production.
Lockheed-built aircraft were designated by a "-LM (Lockheed
Marietta)" suffix and Douglas-built aircraft given a "-DT
(Douglas Tulsa)" suffix. Boeing production was designated by
a "-BW (Boeing Wichita)" suffix, except for the
Seattle-built XB-47s and B-47As, which had a "-BO" suffix.
- The initial batch of 87 B-47Bs featured the same
J47-GE-11 engines as the B-47As, but all subsequent
production featured substantially uprated J47-GE-23
turbojets with 5,800 lbf (26 kN) thrust. Early production
aircraft were retrofitted with the improved engines. They
all featured the built-in RATO system used on the XB-47 and
- All featured full combat systems. Early production
retained the K-2 BNS installed on some of the B-47As, but
most production featured the K-4A BNS, which featured an
AN/APS-54 warning radar and an AN/APT-5 electronic
countermeasures (ECM) system.
- The K-4A used a periscopic bombsight fitted into the tip
of the nose of the aircraft, with the transparent plexiglas
nose cone of the XB-47 and B-47A replaced by a metal nose
cone. There were four small windows on the left side of the
nose and two on the right. Another visible change from the
earlier models was that the B-47B had a vertical tailplane
with a squared-off top, rather than a rounded top as with
- The bomb bay of the B-47B was shorter than that of the
XB-47 and B-47A, since nuclear weapons had shrunk in the
interim. However, the B-47B could carry a much larger bomb
load, of up to 18,000 lb (8,200 kg). All B-47Bs carried the
tail turret with twin 20 mm (0.79 in) guns and the B-4
radar-guided FCS. The B-4 FCS proved troublesome, in fact so
troublesome that in some B-47Bs it was replaced with an N-6
optical sight. The copilot could swivel his seat around to
face backward and sight the guns directly.
- In practice, even the enormous fuel capacity of the B-47
was still not enough to give it the range the Air Force
wanted, and in fact there had been substantial prejudice
against the type among the senior Air Force leadership
because of the limited range of the initial design. Solution
of this problem was a high priority, and so an "in-flight
refueling (IFR)" receptacle was fitted in the right side of
the nose for "boom"-style refueling from KB-50 and KC-97
aircraft. This was the main reason for the deletion of the
plexiglas nose cone for the bombardier navigator.
- The B-47B was also fitted with a pair of jettisonable
external tanks, carried between the inboard and outboard
engine assemblies. These external drop tanks were very
large, with a capacity of 1,780 gal (6,750 l).
- The B-47B suffered a considerable gain in weight
compared to the B-47A, and so as a weight-reduction measure
the ejection seats were deleted, and a windbreak panel was
fitted to the aircraft's main door to make escapes easier.
Some sources also claim that a fatal ejection-seat accident
in a B-47A contributed to this decision. Whatever the case,
this was not a very popular measure with crews, as getting
out of the aircraft even at altitude was troublesome.
- The Air Force had considered building a specialized
RB-47B reconnaissance variant to complement the B-47B
bomber version, but as it turned out schedule slips and
the like ensured that the RB-47E was the first
production reconnaissance variant. As an interim measure
before the RB-47E went into service, 24 B-47B bombers
were fitted with a heated pod with eight cameras that
was stowed in the forward bomb bay, and these aircraft
were designated RB-47Bs. They were capable of daylight
- A total of 66 B-47Bs were also converted into TB-47B
trainers, through the simple measures of adding a fourth
seat for an instructor and removing the tail turret.
These aircraft provided valuable crew training through
most of the 1950s.
- With the introduction of the hydrogen bomb, the USAF
contemplated the conversion of a few B-47Bs into MB-47B
drones, which would essentially be huge cruise missiles
carrying H-bombs. The program was known as "Brass Ring".
Closer examination of the scheme showed that it was
impractical, and Brass Ring was cancelled on the
appropriate date of 1 April 1953.
- There were various flight tests through the 1950s
for using the B-47B as a launcher for the big 31 ft
(9.5 m) liquid-fueled AGM-63 Rascal missile, and one
B-47B was modified to become a YDB-47B Rascal launcher.
However, the Rascal program was politically problematic,
and never became operational, though a total of 74
B-47Bs were modified into DB-74B Rascal launchers before
the program got the axe.
- In 1956, a single B-47B was converted into a WB-47B
weather reconnaissance aircraft and operated by the
Military Air Transportation Service (MATS), making it
one of the few B-47s that wasn't operated by SAC. This
aircraft remained in service with the Air Weather
Service of the Military Airlift Command (MAC) until the
- In 1953, two B-47Bs were modified for testing the
probe-and-drogue refueling system. The tanker was given
the designation KB-47G and was known as "Maw" by flight
crews, and was fitted with a British-built tanker kit.
The refueling test aircraft was given the designation
YB-47F and was known as "Paw", though other aircraft
were also used as refueling targets. The program was
cancelled in 1954 as it turned out the KB-47G simply
could not carry enough fuel to make it a useful tanker.
The idea of fielding B-47 tanker conversions came up
again a few years later, but the economics didn't make
sense, and the notion was finally put to rest for good
- Canadair CL-52
- One of the most unusual B-47B conversions was the
Canadair CL-52 which was a B-47B loaned in 1956 to the
Royal Canadian Air Force to test the new, powerful
Orenda Iroquois turbojet (rated at 19,250 lbf (85.6 kN)
dry, 25,000 lbf (111 kN) afterburning) for the Avro
Canada CF-105 Arrow interceptor. Canadair Aircraft, the
sub-contractor, attached the Iroquois engine to the
right side of the rear fuselage near the tail; due to
the large exterior diameter of the engine, no other
location was feasible. Flying the CL-52 was reportedly a
nightmare. After the Arrow project was cancelled in
early 1959, the B-47B/CL-52, with about 35 hours of
engine flight tests to its credit, was returned to the
U.S. Some sources claimed it was bent out of shape by
the tests, but in any case, it was subsequently
scrapped. The CL-52 was the only B-47 to be used by any
- YB-47C / RB-47C / B-47Z / B-56
- A four-engine variant of the B-47, the YB-47C, was
proposed by Boeing in 1950 to be powered by four Allison
J35-A-23 turbojet engines, providing 10,090 lbf (45 kN)
thrust each, in place of the six GEs J47s. The Allison J35
turbojet engine was being developed during the late 1940s,
and it was provisionally rated at 9700 pounds (with
afterburner) or 8500 pounds thrust without AB. Thus 4 * 8500
= 34,000 pounds using that engine, as compared to 6 * 5200 =
31,200 pounds in the production B-47. So the conversion
would be lighter, simpler and more powerful J71-A-5
- A contract was signed with Boeing in January 1950,
calling for rework of one aircraft. A B-47B-20-BW (s/n
50-082) was earmarked for the conversion. The date for first
flight was projected as April 1951.
- A combination of delays and less-than-expected
performance of the J35 led to the consideration of other
engines. The Allison J71 was proposed, however problems with
this engine meant that this was not feasible for the by-then
re-designated B-56A. The Pratt & Whitney J57, eventually
rated at 17,000 pounds thrust, was also considered, but that
engine was still in development, and the Boeing B-52
Stratofortress, which was being concurrently developed
(first flight was April 1952), had priority for this engine.
- The B-56 was cancelled in December 1952 before
conversion of the prototype was started.
- Beginning in 1951, two XB-47Ds were modified from B-47Bs
as purely experimental platforms, with a big Wright YT49-W-1
turboprop engine spinning a huge four-paddle prop, replacing
each of the inboard two-jet pods. Difficulties with engine
development delayed first flight of the XB-47D until 26
August 1955. The aircraft's performance was comparable to
that of a conventional B-47, and its reversible propellers
shortened the landing roll, but the USAF did not follow up
- The designations B-47C and B-47D were applied to special
variants that never went into production (described later),
and so the next production version of the B-47 was the
- The first B-47E flew on 30 January 1953. Four "blocks"
or "phases" of the B-47E were built, each incorporating
refinements on the previous block, and also sometimes
featuring production changes within a block. Older blocks
were generally brought up to the specifications of later
blocks as they were introduced.
- Early production "B-47E-Is" also known featured
J47-GE-25 turbojets with 5,970 lbf (27 kN) thrust, but they
were quickly changed to J47-GE-25A engines, which featured a
significant improvement in the form of water-methanol
injection. This was a scheme in which a water-methanol mix
was dumped into the engines at takeoff, increasing
mass flow and so temporarily kicking the thrust up to
7,200 lbf (32 kN). Methanol was apparently added to the
water as an anti-freezing agent. The engines left a trail of
black smoke behind them when water-methanol injection was
- Jet-Assisted Take Off or JATO modifications were
performed on early B-47E-Is. They had the 18 built-in JATO
bottles, and were quickly exchanged for an external,
jettisonable "split V" or "horse collar" rack fitted under
the rear fuselage. The rack carried 33 JATO bottles, in
three rows of 11 bottles. The built-in JATO system was
eliminated because of worries about having the JATO bottles
so close to full fuel tanks, and in any case once the rocket
bottles were exhausted they were just dead weight. The racks
were expendable, and were dropped over specific range areas
- The internal fuel capacity of initial production B-47Es
was cut to 14,627 gal (55,369 l) as a weight-saving measure.
This was considered acceptable because of the use of the big
external tanks and the fact that the USAF had refined
mid-air refueling to the point where it could be relied upon
as a standard practice.
- One welcome change in the B-47E relative to the B-47B
was the return of the ejection seats, the Air Force senior
leadership having reconsidered the earlier decision to
delete them. In addition, the twin .50 in guns (12.7 mm) in
the tail turret were replaced with twin 20 mm (0.79 in)
cannon to provide more firepower, backed up by an A-5 FCS in
early production and an MD-4 FCS in later production.
- A final change in the B-47E was that most of the windows
in the nose were deleted, with only one left on each side.
However, many pictures of B-47Es show them with the full set
of windows used on the B-47B. Whether the number of windows
varied through B-47E production, or whether these were
B-47Bs updated to B-47E specification, is unclear.
- The B-47E-II featured only minor changes from late
production B-47E-Is. The B-47E-III featured an ECM suite,
consisting of a radar jammer in a bulge under the fuselage
chaff dispenser, as well as improved electrical
- The B-47E-IV was a much more substantial update,
featuring stronger landing gear, airframe reinforcement,
greater fuel capacity, and a bomb load uprated to 25,000 lb
(11,300 kg), though the bomb bay was once again shortened
because of the introduction of more compact nuclear weapons.
- Another improvement was the introduction of the MA-7A
BNS, a major step up from its predecessors. The MA-7A
included the AN/APS-64 radar, with a range as long as 240 mi
(390 km). The AN/APS-64 could be used as a long range
"identification friend or foe (IFF) transponder"
interrogator to allow a B-47E-IV to find a tanker or other
B-47, or it could be used as a high-resolution
ground-targeting radar. The B-47E-IV retained the optical
bombsight, though this was rarely used.
- A total of 1,341 B-47Es were produced. 691 were built by
Boeing, 386 were built by Lockheed, and 264 were built by
Douglas. Most B-47Bs were rebuilt up to B-47E standards.
They were given the designation of B-47B-II, though it
appears that in practice they were simply called B-47Es.
- TEE TOWN B-47E
- In 1955, a number of B-47E-Is were fitted with
external pods, one mounted on either side of the bomb
bay, with each pod containing four AN/ALT-6B jammers.
The pods were known as "Tee Town pods" (for Topeka, KS,
location of Forbes AFB) and so these aircraft were known
as "Tee Town B-47s". They retained their normal bombing
- The Tee Town B-47s then led to a specialized ECM
conversion of the B-47E, which was given the designation
EB-47E. The initial EB-47 conversion featured a set of
16 jammers in a removable cradle stored in the bomb bay,
plus radar warning receivers and chaff dispensers. These
were known as "Phase IV" or "Blue Cradle" EB-47Es. The
more advanced "Phase V" EB-47E featured a pressurized
module that was stowed in the bomb bay, with 13 jammers
under control of two Crows. While the Phase IV jammer
system was "broadband", blanketing a wide range of
frequencies in hopes of jamming radars operating
somewhere within that range, the Phase V jammer system
could be selectively tuned to specific radar frequencies
by the crows, permitting much higher jammer power on the
frequencies that did the most good. A radar jammer tends
to announce its presence and location by the radio
signals it emits, and EB-47E crews were perfectly aware
that they were unlikely to return from an operational
mission into the USSR. If they could cover for B-47
bombers, however, the sacrifice would be worth it. About
40 B-47Es were converted to EB-47Es. Of course they
couldn't carry bombs, but they did retain the tail
- B-47E 52-0410 and 52-0412 were converted to EB-47Es
in the mid-1960s for service with U.S. Navy's Fleet
Electronic Warfare Support Group (FEWSG). Considered to
be on indefinite loan from USAF, these aircraft were
unlike the USAF EB-47Es, with some of their ECM gear
fitted into pods carried on the external fuel tank
pylons. They were used for tests of naval ECM systems
and as "electronic aggressors" in naval and joint
exercises. These two aircraft were the last B-47s in
operational service, and 52-0410 performed the very last
operational flight of a B-47 on 20 December 1977 when it
was flown to Pease AFB, NH and put on display at the
main gate. Following the closure/realignment of Pease
AFB in 1991 and its conversion to Pease International
Tradeport and Pease ANGB, this aircraft was disassembled
and trucked to Ellsworth AFB, SD where it donated its
nose and engines to RB-47H 53-4299, which is in the
National Museum of the United States Air Force at
Wright-Patterson AFB in Dayton, OH.
- Three B-47Es were converted to the highly
specialized EB-47E(TT) "Tell Two" configuration to be
used for "telemetry intelligence", picking up radio
signals from Soviet missile tests and space launches.
The Tell Two was the precursor to the RC-135S Rivet Ball
and Cobra Ball. The EB-47E(TT)s featured a "Crow
capsule" in the bomb bay loaded with the appropriate
gear and two ECM operators (known as Crows), and also
featured odd and distinctive antennas just below each
side of the cockpit. All three of these aircraft were
operated out of Turkey, and stayed in service until
1967. The antennas on the nose of the aircraft attracted
a good deal of attention from base personnel, and crews
made up imaginative stories about them, for example
claiming they were part of a "return to fighter (RTF)"
defensive system that would cause Soviet air-to-air
missiles to loop back and shoot down their own launch
fighters. In reality, they were specialized receiver
antennas used for intercepting telemetry signals from
Soviet space and missile launches.
- As with the B-47B, a few B-47Es were converted to
trainers, with a fourth seat for an instructor, and
given the designation ETB-47E. These aircraft were used
to replace TB-47Bs that had "got too long in the tooth,"
and served into the early 1960s.
- DB-47E / YDB-47E
- Two B-47Es were converted to YDB-47Es to support the
GAM-63 RASCAL stand-off missile program, and two more
B-47Es were converted to DB-47Es in preparation for the
operational introduction of the missile before the
program was axed. These two DB-47Es were later used as
drone controller aircraft.
- Several B-47Es were assigned to other specialized
test duties and given the blanket designation of JB-47E.
One was used in the late 1960s to test "fly by wire"
control system concepts.
- Two B-47Es were also used for secret flight
experiments in the early 1960s and given the designation
JTB-47E, and a third, even more mysterious modified
B-47E was given the designation JRB-47E. They appear to
have been test platforms for ECM systems.
- Finally, a B-47E was loaned to the U.S. Navy to help
test the GE TF34-2 turbofan for the Lockheed S-3 Viking
carrier-based antisubmarine warfare aircraft. This B-47E
was given the designation NB-47E and performed test
flights from 1969 through 1975.
- A total of 14 B-47Es were converted to QB-47E target
drones in 1959 and 1960. These aircraft were
radio-controlled, and included such interesting features
as self-destruct charges and arresting gear to assist in
landings. They also carried pods mounted on the external
tank pylons to help in scoring weapons tests. Apparently
most of the missiles fired on them were directed for a
near-miss, but the QB-47Es were nonetheless eventually
whittled down to two survivors that were retired in the
- On 20 August 1963, a QB-47 veered off course on its
landing approach at Eglin Air Force Base and crash
landed on a stretch of road that ran parallel to the
runway. Two cars were crushed by the crash landing,
killing two occupants, Robert W. Glass and Dr. Robert
Bundy, and injuring a third, Dorothy Phillips. Mr. Glass
and Dr. Bundy both worked for the Minnesota Honeywell
Corporation at the time, a firm which had just completed
flight tests on an inertia guidance sub-system for the
X-20 Dyna-Soar project at the base. Mrs. Phillips was
the wife of Master Sergeant James Phillips, a crew chief
at the base. Mrs. Phillips was treated for moderate
injuries and released later that day. Both vehicles were
destroyed by fire. The QB-47 that crashed was used for
Bomarc Missile Program tests, which normally operated
from Eglin AFB Auxiliary Field Number Three (Duke
Field), approximately 15 miles (24 km) north of the main
- The B-47E was also the basis for a number of
important long-range reconnaissance variants. The only
B-47s to see anything that resembled combat were these
reconnaissance variants. They operated from almost every
airfield that gave them access to the USSR, and often
probed Soviet airspace.
- Boeing-Wichita built 240 RB-47E reconnaissance
variants, similar to the B-47E but with a nose stretched
by 34 in (0.86 m), giving them an arguably more elegant
appearance than the bomber variants of the B-47. The
long nose was used to stow up to 11 cameras, which could
- An O-15 radar camera for low-altitude work.
- A forward oblique camera for low-altitude work.
- A K-17 trimetrogon (three-angle) camera for
- K-36 telescopic cameras.
- The RB-47E could carry photoflash
flares for night reconnaissance. Although the RB-47E
could be refueled in flight, its fuel capacity was
increased, to a total of 18,400 gal (70,000 liters). The
navigator controlled the cameras, becoming a
"navigator-photographer" instead of a
- Following the single WB-47B weather reconnaissance
conversion, in the early 1960s 34 B-47Es were converted
by Lockheed into WB-47Es for weather reconnaissance.
These aircraft were stripped of combat gear, including
the tail turret. They were fitted with cameras in the
nose to take pictures of cloud formations, and carried a
special meteorological instrument pod in the bomb bay.
Initially assigned to the Air Weather Service of the
Military Air Transport Service (MATS), they became part
of the Military Airlift Command (MAC) when that
organization was established. The last WB-47E was
retired on 31 October 1969, and was the last B-47 in
operational USAF service.
- A total of 32 RB-47H models were built for the
electronic intelligence (ELINT) mission, as well as three
more specialized "ERB-47Hs". These aircraft featured
distinctive blunt, rounded nose and sported blisters and
pods for intelligence-gathering antennas and gear. They were
designed to probe adversary defenses and then collect data
on radar and defense communications signals.
- The bomb bay was replaced by a pressurized compartment,
which accommodated "electronic warfare officers (EWOs)",
also known as "Crows" or "Ravens" (both being black birds,
it was a reference to "black ops" meaning classified
operations). There were three Crows on board the RB-47H, but
only two on the ERB-47H. A distinctive bulged radome fairing
replaced the bomb bay doors. The RB-47H / ERB-47H retained
the tail turret, and were also fitted with jammers and chaff
dispensers. The only easily recognizable difference in
appearance between the RB-47H and ERB-47H was that the
ERB-47H had a small but distinctive antenna fairing under
the rounded nose.
- The first RB-47H was delivered in August 1955 to Forbes
AFB, Kansas. The ELINT B-47s proved so valuable that they
were put through a "Mod 44" or "Silver King" update program
in 1961 to provide them with updated electronics systems.
Silver King aircraft could be easily recognized by a large
teardrop pod for ELINT antennas attached to a pylon, mounted
under the belly and offset to one side of the aircraft, as
well as a pylon-style antenna attached under each wing
beyond the outboard engine. It is unclear if all RB-47Hs and
ERB-47Hs were updated to the Silver King specification.
- The RB-47H and ERB-47H were highly capable aircraft, but
the EWO compartment was not only cramped with sitting room
only, but also had both poor noise insulation and climate
control. This made 12-hour missions very uncomfortable and
tiring, and some sources say that the Crows even had to deal
with fuel leaks on occasion. Successful ejection downward
(cutting through the belly radome) was impossible on-or-near
the ground. Crows sat bobsled-like on the pilot compartment
access floor for takeoff and landing; having to crawl
encumbered with Arctic clothing with parachute to-from their
compartment along an unpressurized maintenance shelf during
temporary level off at 10,000 ft (3,000 m)
Operations of the RB-47H and ERB-47H were often classified
Top Secret, with the 10 hour missions generally flown at
night. When crews were asked what they were doing, they
always answered that such information was classified. On
inquiries on what the blunt black nose was for, they would
sometimes reply that it was a bumper, used in in-flight
refueling in case they nosed into the tanker. This reply was
- The final RB-47H to be retired from service was later
pulled out of the "boneyard" and used for tests of avionics
for the General Dynamics FB-111. This RB-47H was fitted with
an F-111-style nose and flew into the early 1970s. It was
not given any special designation. It is now on display at
the Air Force Armament Museum at Eglin AFB, Florida, fitted
with a bomber nose.
- A single B-47E was modified to test the MA-2 BNS for the
B-52, and given the designation YB-47J. Other B-47Es were
also apparently used in the MA-2 tests, but not given a
- The RB-47Ks were generally used for weather
reconnaissance missions, carrying a load of eight "dropsonde"
weather sensors that were released at various checkpoints
along the aircraft's flight path. Data radioed back from the
dropsondes was logged using equipment operated by the
navigator. The RB-47Ks stayed in service until 1963.
- In 1963, the Air Force modified 35 B-47Es to carry a
communications relay system. These aircraft were given the
new designation of EB-47L, and were used to support U.S.
flying command post aircraft in case of a nuclear attack on
the US. The EB-47Ls only remained in service for a few
years, as improved communications technologies quickly made