The GE90 was developed from the NASA 1970s Energy Efficient Engine, a prototype variant of the General Electric CF6. GE's GE36 Un-Ducted Fan (propfan) was meant to replace the CFM International CFM56 high-bypass turbofan which was initially uncompetitive against the rival IAE V2500. However, when the V2500 ran into technical problems, sales of the CFM56 took off. GE was not interested in having the GE36 cannibalize the CFM56, and while "the UDF could be made reliable by earlier standards, turbofans were getting much, much better than that." However, GE integrated the UDF's blade technology directly into the GE90.