That just means they burn a lot of fuel. Generators can burn the same diesel as a boat, and most can burn Jet A, too.
Where do you think they get the electricity for the bases now?
Usually from power plants, although they sometimes use generators when off-site power has outages. One of the Air Force bases near me recently installed a specifically designed multi-fuel generator: https://www.afmc.af.mil/News/Article-Display/Article/4421866...