General Electric TF39

On September 7, 2017, the last active C-5A powered with TF39 engines made its final flight to Davis-Monthan Air Force Base for retirement.

The United States Air Force opened the "CX-X Program" in 1964, intending to produce a next-generation strategic airlifter.

The high-bypass turbofan was a huge leap in engine performance, offering a thrust of 43,000 pounds, while improving fuel efficiency by about 25%.

It introduced use of a large by-pass ratio which, together with advances in core technology, contributed to a significant improvement in fuel efficiency over engines available at the time.

By modern standards the Low Pressure Compressor on the TF-39 is fairly unique as a single T-stage is mounted upstream of the fan rotor, rather than behind it.

TF39s on a C-5 Galaxy, from the rear
TF-39 on display at the Museum of Aviation View looking into the fan showing snubbered blades on the inner half-stage and inlet guide vanes in the outer duct in front of the full stage.
A Boeing B-52E (Serial Number 57-0119) testing a TF39 on the right inboard engine pod. The TF39 has more than double the thrust of the twin Pratt & Whitney J57s that were originally in that spot.