Developed as a stand-alone single section of the
T40 (Model 500) twin engine to aid in development of the T40, the T38 started life with a 19-stage axial compressor, eight can type combustion chambers, a 4-stage turbine driving the compressor and the extension shaft to the reduction gearbox. Initially rated at the T38 first ran in 1947 and flew in the nose of a
Boeing B-17 Flying Fortress test-bed on 19 April 1949, rated at . Problems with gearbox vibration and combustion were dealt with during the test program and were mirrored by problems with the
T40, which had a pair of T38 power sections feeding a common gearbox. The engines fitted to the
Convair CV-240-21 Turboliner were rated to equivalent. Although the only other aircraft slated to receive the T38 as a production engine, the
Convair T-29E, was cancelled, the T38 did power a converted
Convair CV-240 (the CV-240-21 Turboliner, a project that would be abandoned due to engine problems), and was fitted in the nose of the
McDonnell XF-88B to drive experimental supersonic propellers. Further development of the T38 provided the power sections for the Allison T40 as well as forming the basis for the
Allison T56/Model 501 and the projected
Allison T39. ==Variants==