 Based on the testing and evaluation of the XF-104, the next variant, the YF-104A, was lengthened and fitted with a General Electric J79 engine, modified landing gear, and modified air intakes.The YF-104A and subsequent models were longer than the XF-104 to accommodate the larger GE J79 engine.The YF-104 initially flew with the GE XJ79-GE-3 turbojet which generated 9,300 pounds of dry thrust (14,800 with afterburner), which was later replaced by the J79-GE-3A with an improved afterburner.