[boomop1]

They old when I flew them in the 60s and 70s the KC-135A would eat over a mile of runway by the time we lifted off heavy weight.

[El Gato]

They old when I flew them in the 60s and 70s the KC-135A would eat over a mile of runway by the time we lifted off heavy weight.

That's a little better with the -Es and much better with the -Rs. The main benefit of the -Es (which are just -As re-engined with JT3Ds (military designation is a TF33 varient) taken off of old 707 airliners, is decreased fuel burn, which translates into increased range and/or increased fuel offload. The -Rs are more extensively modified, but part of that was re-engining with CFM56 (military designation F108) which gives the same benefits as for the -Es, but much more so. They can also take off at higher weights and/or use less runway.