I saw a 747 parked next to a C5A at Kadena, Okinawa. Same size and the 747(like ivermectin) was much cheaper and available. .
Yes, like ivermectin is to medicine, the 747 is a true cost-saving, proven aviation platform. It’s a legend, both in the civilian world and as a frequent military charter aircraft (mostly for pax).
Or at least used to be. It’s not fuel-efficient compared to the modern two-engine jets like the long-range 777 or 787. Then again neither is the C-5, even the C-5M Super Galaxy (re-engined with GE CF6-80C2 commercial-grade engines, same engine family used on 747s and other airliners).
C-5 Galaxy - 285,000 lbs ~34,000 cubic feet
747-8F (Freighter) - 292,400 lbs- ~30,288 cubic feet
The 747 carries slightly more weight but “cubes out” earlier.
The C-5 can load two M-1 tanks, loaded through the front once the cockpit is swung upwards. The 747 doesn’t have drive-on ramps like the C-5 or C-17.
Like other military transports (C-141 (obsolete)/C-17/C-5) it has a T-tail, enabling direct loading from the ramp from aft. It doesn’t require a loader like the 747, speeding up the process. The T-tail was the result of Army specs in the design phase.
Unfortunately the T-tail means it’s slower at cruise. Mach .77 is normal. For the 747, mach .84. And the T-tail is problematic during in-flight refueling, with the T-tail in the wake turbulence of the KC-10, KC-135 or KC-46A. Heavyweight A/R is about 10 times the wear-and-tear of normal cruise on a T-tail jet.
No 747 can refuel in flight.
The C-5 is notoriously unreliable compared to just about any 747.