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Two 20-mm M-24A-1 guns and 700 rounds with General Electric APG-32 gun-laying radar tail turret replaced the twin .50s and A-5 system of earlier models. The co-pilot turns his seat to the rear, when the warning radar indicates hostile aircraft. The search radar computer is provided with air temperature, altitude and air speed information. When a bright spot on the screen shows that the radar has picked up an attacking plane, the gunner can locked on to the target, which is tracked automatically until the hostile aircraft enters gun range and the guns can fire.

The RB-47E first flew on July 3, 1953, with elongated nose, 11 cameras, twin 20-mm guns and A-5 fire control, but no bombs. Beginning with the 862nd Stratojet in February 1955, MA-7A bombing radar was installed, and this model became the B-47E-IV. Heavier landing gear permitted an increase in takeoff weight from 99 to 113 tons, giving a 2,360-mile combat radius with full tanks. BOEING RB-47K-BW

Production included 691 B-47E-BWs, 386 B-47E-LMs, 264 B-47E-DTs, and 240 RB-47E-BWs. The YB-47F receiver and KB-47G tanker, however, were B-47Bs modified to test the probe-drogue in-flight refueling system.

Cold War Overflights
By 1956, the nuclear bomb stockpile held over 3,500 warheads, including Mk. 15, 28, 36 and 43 models that could fit the B-47 bomb bay. But the B-47 never had to drop a bomb in combat. Instead, it made some of the Cold War’s most dangerous missions; actual overflights over the USSR. President Truman had authorized prehostility strategic reconnaissance during the Korean War, fearful that Tu-4s with atomic weapons might be grouped in Siberia for a surprise attack on America. Since overflights were a deliberate violation of international law, they were kept secret for many years. BOEING RB-47H-1-BW

The fourth B-47B was provided with a bomb bay camera pod and special instruments and flown to Alaska, but before its mission, was destroyed by an accidental fire on August 15, 1951. Two more B-47Bs were modified in 1952 and, accompanied by KC-97 tankers, moved to Alaska by 306th BW crews. On October 15, 1952, they photographed bases in Eastern Siberia, and discovered no bomber threat.

In 1954, concern about a possible M-4 jet bomber concentration led to a bold RB-47E sortie from Britain over the Kola Peninsula on May 8. Despite damage from MiG-17 interceptors, the crew completed their mission. More SAC RB-47E overflights were accomplished from Alaska in Project Seashore, starting on March 30, 1955.

Beginning in June 1955, 35 RB-47H models were completed as electronic reconnaissance aircraft. These aircraft carried an additional three men (called Crows!) in the bomb bay, with equipment to locate and analyze enemy radar. Project Homerun, flying from Thule, Greenland, over the Arctic to the Soviet coast from March 21 to May 16, 1956, used 16 RB-47Es from the 10th SRS and five RB-47Hs from the 343rd SRS. SAC’s 156 Homerun sorties included a bold formation of six RB-47Es on May 6.

However, an RB-47H shot down by MiG-19s over the Barents Sea on July 1, 1960, was on an ELINT mission, not an overflight. These sorties were intended to provoke VVS reaction, so that hostile radar could be analyzed. About 40 RB-47Es became EB-47Es when fitted with elaborate radar jamming antennae; they were planned to divert an enemy from any SAC bomber thrusts.

Cold war tensions reached the point where part of the B-47 squadrons dispersed around the world were kept on a 15-minute alert. To evade enemy radar, new mission profiles focused on low-altitude penetration, with nuclear bombs delivered by “pop up” or LABS techniques. MARTIN XB-51

Many Stratojet modifications were tried. One YDB-47B and two YDB-47Es were modified to carry a radio- controlled Bell Rascal (GAM-63) air-to-surface missile on the fuselage starboard side. The first successful launching of the ten-ton missile with a 100-mile range was made February 17, 1955, but the Rascal was canceled November 29, 1958, in favor of the Hound Dog program.

A single YB-47J was modified to test an MA-2 radar system and 15 RB-47Ks were the last RB-47Es modified for inflight transmissions of weather data and collecting samples from foreign nuclear blasts. The first was delivered in January 1955. The EB-47Ls were “post-attack communication relay stations” converted from 36 B-47Es in 1962-63.

A total of 2,041 Stratojets were built. When SAC received its last production-line Stratojet, a B-47E, on February 18, 1957, it had 28 Medium Bomb and five Medium Strategic Reconnaissance Wings, with about 1,306 B-47 and 254 RB-47 aircraft. SAC retired its last B-47E in February 1966 and its last RB-47H in December 1967, although a few remained in non-combat roles elsewhere. The B-47’s most important legacy was the technical experience that enabled Boeing to lead the world in jet airliners, and to produce the B-52 bomber.

Light Bombers Revived
When the Korean War ended in 1953, the 29 USAF bomber wings included ten with B-29 and five with B-50 medium bombers, five with intercontinental B-36s, and four with the new B-47. Propeller-driven Douglas B-26 Invaders filled the three wings assigned to short-range light bombing, and Tactical Air Command (TAC) had only one B-45 jet bomber wing with nuclear weapons.

Two such projects had been started under the old “Attack” category: Convair’s XA-44 and Martin’s XA-45. Redesignated XB-53 in 1948, the Convair was an odd canard design with three J35 jets and a swept-forward wing that was canceled before completion. Martin’s XA-45 had been proposed on April 1, 1946, as a straight-winged, six-place bomber with two TG-110 turboprop and two I-40 turbojets, but by February 1947 that design had been replaced by a smaller swept-wing, two-place design with three jet engines. 2nd MARTIN XB-51

This became the XB-51, whose mockup was inspected in February 1948 by the Air Force, which directed Martin to go ahead with two prototypes on April 23, 1948. Two J47-GE-13s were attached below the fuselage, with a third in the tail. Wings were swept back 35 degrees, had a 6-degree cathedral (droop), and their incidence could be increased for takeoff and landing. Instead of ailerons, spoilers were used along with leading-edge slats and full-span slotted flaps. Tandem dual main wheels, like those on the B-47, were provided, along with a high T-tail. The pilot sat under a bubble canopy and the navigator was placed behind and below him within the fuselage.

Eight 20-mm nose guns had 160 rpg and up to 10,400 pounds of bombs could be carried in a unique rotary bomb bay door, with the basic mission the delivery of 4,000 pounds over a 435-mile radius. Flight tests began October 28, 1949, with the second, slightly modified, example flown the following April 17. But in 1951 the Air Force decided to terminate the XB-51 in favor of another program.

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