You are falling apart... They call it an E-6 these days

The E-6 is based on the 707, not the -135.

Larger tankers? Oh, you mean the KC-10s. The AF doesn't have that many
as
they are REALLY, REALLY expensive. They are primarily used to transport
Fighters across the Oceans. Since most of the KC-10s are assigned to the
AF
Reserves, those are not the ones near the War Zones. The KC-135, P-3 and
the KC-130 handle it closer to the action. The fact is, the P-3 and the
KC-130 operate almost right on the front lines while even the KC-135
operates further behind the lines. Due to financial reasons, it's better
to
lose a P-3 Orian or a KC-130 over a KC-135. At least those two only cost
a
few million where as the KC-135 cannot be replaced.

The KC-10 was a bargain at (about) $60 million apiece. Cheap compared to the
767 which won't come close to the Ten's offload capability.
Fighter drags are the Ten's first mission but we do much more theater
refueling and even cargo hauling.
No KC-10s are assigned to the reserves. Both bases (McGuire & Travis) have
an associate reserve unit but I can assure you the active duty units "own"
the airplanes.
KC-130s generally operate in higher threat areas due to the nature of the
mission, not financial reasons. Howwever, plenty of KC-135s & KC-10s go in
harm's way when the mission calls for it.

Curt
KC-10 flight engineer