The
KC-135 Stratotanker aircraft is built on the
U.S. Air Force's common -135
airframe. Any aircraft with -135 in its U.S. military designation (see
Aircraft Designations) is built on the precursor to the
Boeing 707 airframe. The large number of planes that share this base type makes for savings in common parts and maintenance tools, training and facilities. However, the
707 airframe is approaching forty years of age, and has not been
manufactured in quite some time. Although there is a large pool of civilian airframes available used for
remanufacturing or parts, the U.S. Air Force has begun moving its large-body platforms to the more widely available (and still manufactured)
Boeing 747 base airframe. Aircraft built on this pattern carry the designation suffix 'C-25.'
Air Force One is usually one of two VC-25 aircraft maintained and modified for the purpose of transporting the
POTUS or other
VIPs.
Some other aircraft that share the -135 designation:
It should be noted that the 'Strato' prefix in the type name is used on other related airframes, notably the B-52 Stratofortress. The prefix is taken from 'stratosphere', the layer of the atmosphere that these aircraft were aspirationally to be operated in. At the equator, this layer starts at approximately 60,000 feet depending on conditions, which is not likely; however, at approximately 45 degrees of latitude, the stratosphere can be found as low as 33,000 feet which is absolutely within their operating envelope.