According to Robert Hopkins' book "Boeing KC-135 Stratotanker - more than
just a Tanker" published in 1997:
62-4126 First flew on 18th May 1962. Delivered on 29th May 1962. Assigned
in 1967 to 1st MAS 89th MAW at Andrews AFB. Configured with a VIP interior
and redesignated VC-135B Redesignated C-135B on 1st December 1977 un-
der the Carter Administration's "low profile" effort. Transferred in September
1991 to the 55th Wing at Offutt AFB as a CSA*. Since transferred to the
21st AF at McGuire AFB for an unidentified transport mission, possibly with
the On-Site Inspection Agency (OSIA) or for discreet VIP operations, with
crews from the 141st AREFS 108th AREFW, New Jersey ANG.
*CSA - Command Support Aircraft
Checking the database of all USAF serial numbers, this aircraft is listed as
having begun conversion to TC-135S in January 2004.
In God we trust.
All others we monitor.