Tail code

Tail code "ET", for "Eglin Test", as seen on the tails of F-15EX and F-15E under the 96th Test Wing stationing in Eglin AFB.

Tail codes are markings usually on the vertical stabilizer of U.S. military aircraft that help identify the aircraft's unit and/or base assignment. This is not the same as the serial number, bureau number, or aircraft registration which provide unique aircraft identification.