The C-5 fuel tanks are pressurised with nitrogen for fire suppression and tank inerting. Something like 1.5 psi. It is a nightmare for the guys who try to keep the system running. The aircraft is serviced with liquid nitrogen, stored in 2 dewars, and converted to a gas for tank inerting. I think each dewar is 750 litres. The hassle to keep valves and seals in the liquid nitrogen system working is a problem, since you are dealing with a cryogenic. This system does not help with fuel feed, gravity can feed the engines from the main tanks, and the engine driven fuel pump can do the rest. The advantage of this setup is no moist air will enter the tank as fuel is used. The vapor space is nitrogen inerted. Almost unheard of to have water in the tanks. Also if something is having a bad day in the tank and is producing an ignition source, it is very hard to make something go boom. I think this airplane is the first and last to have this system. I have been told the C-17 tried something like this by extracting nitro from bleed air, but it doesn't work. If a gravity tank fill cap is taken off, LOTS of air/nitro is expelled. (Enough to mess up your hair).