My dad flew these for ~17 years of his 23 year USAF career, and he flew them in both Operation Desert Shield and Desert Storm. He was also a C-5 test pilot, testing the new production C-5Bs on behalf of the Air Force that were rolling off the assembly line in the late 80s and, later in his career, testing C-5s after they went through depot maintenance; meaning certifying them airworthy after the aircraft had been totally torn down and put back together with whatever parts needed to be replaced. Currently, over half my life has been spent around this big, beautiful aircraft. Always loved it when he took me out to the flight line to crawl around them. The roar of those TF39s send me right back to my childhood. This is the best video I've run across that really captures its distinct sound:
Sadly, that mighty roar won't be heard much longer. The C-5 fleet has been undergoing modernization, which includes being re-engined with CF6s. They're more efficient, powerful, etc. than the TF39s, but the C-5 sounds totally weak now.
And to finish off, here's a pic of my dad taking off for a test flight of a rebuilt C-5 that had suffered an accident.