TB-47B were trainer conversion models of the B-47B production model. At least 66 of B-models were converted as such and saw the loss of their defensive tail armament as well as the inclusion of a fourth position seat for the instructor.
The Stratojet existed in several short-live forms that included the YDB-47B missile launcher platform, the WB-47B weather reconnaissance platform, the KB-47B refueler and the CL-52 from Canadair to be used as a test airframe for the Orenda Iroquois engine to power their (ultimately) cancelled Avro CF-105 Arrow interceptor. Similarly, a B-47E was loaned to the United States Navy for the testing of the GE TF34-2 turbofan engine to be used in the Lockheed S-3 Viking anti-submarine aircraft and designated as the NB-47E. Several specialized ECM conversion models existed and were noted for their "E" designators as in the EB-47E, EB-47E(TT) and ETB-47E. The JB-47E was used to test early fly-by-wire systems while QB-47E were radio-controlled target drones.
Boeing further proposed a four engine variant of the B-47 to be powered by 4 x Allison J35-A-23 turbojet engines of 10,090 thrust each. Engine issues eventually delayed and ultimately cancelled this Stratojet version in December of 1952. The XB-47D was an experimental platform fielding Wright turboprops for the USAF but was never furthered after performance did not improve over that of the original's turbojets.
The markers of B-47C and B-47D were assigned to specialized B-47 variants that were never selected for serial production by the USAF.
The definitive B-47 became the B-47E model. First flight was recorded on January 30th, 1953 fielding J47-GE-25 turbojet engines of 5,970lbf. These were then upgraded to the J47-GE-25A series engines sporting water-methanol injection systems to provide extra thrust during take-off. The original 18 JATO packs were further increased to 33 and could be jettisoned after use. Ejection seats were brought back into the fold. The defensive tail armament was upgraded to a pairing of 20mm cannons. The second B-47E production block differed little when compared to the first while the third block added an Electronic CounterMeasures (ECM) suite and chaff dispenser, the former noted as an under-fuselage bulge. The fourth production block featured a reinforced airframe and landing gear as well as an increased internal fuel capacity and, therefore, longer range. The internal bomb load was increased to an extend as well (25,000lbs) but made smaller to accommodate the smaller technology of newer nuclear ordnance. The B-47E was produced in 1,341 examples with production handled by Boeing, Lockheed and Douglas facilities.
As the B-47B before it, the B-47E was also modified for the reconnaissance role to become theRB-47E to which some 240 examples were built. These were noted for their elongated nose assemblies which housed up to eleven cameras. Night reconnaissance was now possible with the newer RB-47Es. The B-47E was also modified for the weather reconnaissance role as the WB-47E to which 34 were produced.
The RB-47H was an ELINT (ELectronic INTelligence) platform and were joined by a further variant known as the ERB-47H. These were noted for their blistered noses and pressurized bomb bays (serving as a crew cabin) and differentiated by the latter's antenna fairing under the nose. RB-47K were utilized in weather reconnaissance roles up until 1963. The EB-47L was used as an airborne communications relay platform (in the advent of all-out nuclear war) beginning in 1963.
By 1965, the B-47 program had all but run its course, now replaced by the Convair B-58 Hustler and the Boeing B-52 Stratofortress series of bombers (both aircraft detailed elsewhere on this site). Despite this somewhat average span for operational service, the B-47 became a major contributor to the United States Air Force in terms of strategic defense and deterrence. Serving as a capable high- or low-level bomber and reconnaissance platform ensured the system a good historical reputation and paved the way for future American bomber designs capitalizing on the successes pioneered in the groundbreaking B-47.
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