The XB-56 was a re-designated version of the B-47C. Soon after the decision of making XB-56, the authority shifted its interest towards the budding B-52 program.
At the end, the XB-56 program was canceled.
The B-47C program was based on the design of the B-47B; the difference was that the B-47C had Allison J35-A-23 turbojets instead of the six General Electric J47s. Besides this, the inboard engine nacelles were mounted in place of the two J47s on the production B-47B model.
The initial flight of April 1951 was delayed due to engine problems. Engines could not produce thrust as estimated. Preliminary estimates were 9,700lbs, but testing showed the actual thrust was only 7,400lbs. The manufacturer then considered the Allison J71-A-5 and the Pratt & Whitney J57 engines, but by the time testing came about, the interest in the program died due to shifted interest in the B-52 program. The B-52 eventually received the Pratt & Whitney J57 engines.