The B model Stratojet was the first aircraft in the B-47 series that was actually combat ready. The outbreak of the Korean War in June 1950 accelerated production plans for military aircraft in general. The B-47 was no exception as the original order for 87 aircraft was increased to 399. The first 87 aircraft (S/N 49-2642 to 49-2646 and 50-1 to 50-82) were completed with the same engines as the B-47A: General Electric J47-GE-11s of 5,200 pounds thrust each. The rest of the B-47B were fitted with improved -23 J47s of 5,800 pounds thrust each. The original 87 aircraft were refitted with these more powerful engines later.

Besides the more powerful jet engines, the B-47B featured two external fuel tanks -- one on each wing between the inboard and outboard engine nacelles. These tanks held an additional 1,780 gallons of fuel each and were droppable in flight. The -B model Stratojet was also equipped with in-flight refueling capability as well as single point refueling for normal ground refueling.

The first flight of the B-47B was on April 26, 1952. Because of the urgent need for the medium jet bomber, the manufacturing pool used extensively during World War II to build Boeing B-29s was revived. Both Douglas and Lockheed were awarded assembly contracts; however, only 18 aircraft were completed by these two companies (10 by Douglas and eight by Lockheed). The pool was retained for construction of B-47Es, and all three companies built significant numbers of -E model aircraft.

About half of the B-47Bs were bought up to B-47E standards during 1956-57. A new version of the J47 jet engine was installed (6,000 pounds thrust each), avionics upgrades were done, the .50-cal. machine guns in the tail turret were replaced by 20mm cannons, the built-in Rocket Assisted Take Off ports were replaced by a strap-on RATO system, and ejection seats were installed. These modified aircraft were redesignated B-47B-II.