07/31/2018. Remarks by Johan Visschedijk: "In 1955, two KC-97Gs (serials 52-2693, 52-2762) were modified by Boeing at Air Force request to serve as flying test beds in which to accumulate service experience with the 5,700 hp Pratt & Whitney YT43-P-5 turboprop engine. This request was a bit ironic for Boeing, coming as it did practically at the end of C-97 production and long after Boeing had tried to interest the Air Force in turbine power as a means of greatly improving the basic C-97 design.

As it was, the lighter weight and greater power of the turboprops greatly increased the performance of the YC-97J over that of the standard model. The original designation assigned to the modified aeroplanes was YC-97H, but since the power plant change resulted in practically a new design, the designation of YC-137 was tentatively assigned to reflect the more modern features. By the time this was rejected, the H series letter had been assigned to another C-97 variant so the turboprop versions became YC-97J."