[Llarry]

I'm sure our aviation professionals know this, but did you know that the Boeing 707 and the Air Force's C-135 (KC-135, RC-135, etc.) are two different airframes? They have a common progenitor, the Boeing Dash 80, but Boeing decided to make the commercial aircraft just a bit wider. They are close, but not identical.

Later, the Air Force decided to buy not only hundreds of tankers (original Boeing designation the 717): the KC-135A and subsequent versions -- but also a limited number of model 707s. The military designation for the 707 was C-137 and the first ones were purchased for use as presidential transports. Years later, the E-3A Sentry Airborne Warning and Control System (AWACS), also Boeing 707-derived, was purchased in larger numbers and remains in service today. Then the Navy got in on the Boeing 707 bandwagon with the E-6A Mercury, sometimes called the "Doomsday Plane" and bought a small number of those. They are still in service and now have been updated and redesigned E-6B.

The E-6A was designed to communicate to the nation's ballistic missile submarine fleet in case of war: essentially, to give the order to fire the missiles. Thus the term Doomsday Plane. The Air Force had a similar mission using EC-135s to control strategic bombers and ICBMs and, in a case of interservice cooperation, the Air Force mission was integrated with the Navy mission (and the EC-135s retired) and now the E-6Bs communicate with all components of the strategic nuclear triad: ICBMs, bombers and sub-launched missiles.

I've always been fascinated by the way that the E-6 sends messages to submarines. The submarines are submerged, of course, and the only signals that can be received are very low frequency (VLF) signals, which require very large antennas. A problem in an aircraft. The method that is used is that the E-6 spools out an extremely long transmitter wire -- like 25,000 feet long! -- and goes into a tight orbit so that the wire drops from gravity and becomes more or less vertical, as the E-6 turns around the antenna.

Anyway, as befits a critical component of the U.S. strategic forces, the E-6B stays dispersed and on the move (and thus hard for an enemy to take out in a surprise attack.) Here's a photo of an E-6B in its unique paint. From the mid-1950s to the 1980s, Navy tactical carrier aircraft had white undersides -- to better resist structural damage from nuclear flash. I'm not sure that's what's going on here with the E-6B but maybe.