Don Firth and John in Kansas have made some good points. If the Air Force did want bigger, the 777 and indeed the 747 air frames are there.

There are a couple of good reasons for replacing the 707's in the long run.

1. The planes are getting old.
2. That newer planes with the new Ge engines are more fuel efficient.

Then again there is at least one good reason for not replacing them.

1. I think we need to rethink this whole "projection of power" thing and the whole way the Navy and Air Force seem to like to use sledge hammers to crush ants. Do we really need 300 billion dollar B1 bombers flying out of the US midwest and refueled over the Atlantic and 2 billion dollar submarines that were originally designed to carry ICBMs to carry smart bombs and cruise missiles to the mid east.

Wouldn't it make a lot more sense to ship the munitions over there in freighters and then reuse much cheaper tactical assets like Harrier    Hawks and f18's and ground based launchers to carry out such attacks.

If the Pentagon were put on a sensible budget. They wouldn't need or really be able to use so many tankers. It must cost a fortune just to keep those things in the air. And think about global warming for a second. Its wasteful! Its nuts!

2. Most high tech weapons systems, including the bulk of this one, are just corporate welfare and pork and don't really make us much safer. Try spending the money on special forces and Military Police trainers so that countries like Iraq and Afghanistan can police their own oil and poppy fields.