The Boeing EC-135 was a version of the C-135 Stratolifter, modified to operate on several different U.S. Air Force programs.

"Operation Looking Glass" provided at least 11 EC-135C command post aircraft to the Commander in Chief, Strategic Air Command (CINCSAC), which were either based at its headquarters at Offutt AFB, Nebraska, or at Ellsworth AFB, South Dakota. All aircraft have been retired or repurposed.

The U.S. nuclear strategy depends on its ability to command, control, and communicate with its nuclear forces under all conditions. An essential element of that ability is Looking Glass; its crew and staff ensure there is always an aircraft ready to direct bombers and missiles from the air should ground-based command centers be destroyed or rendered inoperable. Looking Glass is intended to guarantee that U.S. strategic forces will act only in the manner dictated by the President. It took the nickname "Looking Glass" because the mission mirrored ground-based command, control, and communications. Besides being the program name, "Looking Glass" is the official name for the "C" model aircraft of the EC-135. It has a crew of at least 15, including at least one or more general officers.

The Strategic Air Command (SAC) began the Looking Glass mission on February 3, 1961 and Looking Glass aircraft were continuously airborne 24 hours a day for over 29 years, accumulating more than 281,000 accident-free flying hours. On July 24, 1990, "The Glass" ceased continuous airborne alert, but remained on ground or airborne alert 24 hours a day.
On June 1, 1992, SAC was deactivated and replaced by USSTRATCOM, which now controls the Looking Glass.[2][3] On October 1, 1998, the Navy's E-6 Mercury TACAMO replaced the USAF's EC-135C in the Looking Glass mission.