But Civil Aircraft do carry transponders that "reply" to pings from controllers on the ground. Many of these can also respond to other nearby aircraft if both are equipped for it. The return specifically identifies the individual airplane. The pilots consider it pretty much an IFF, since by knowing the airplane they know whether to report the time by "which way Mickey's hands point" or to use standard nomenclature. (Pilots are a little like truckers.)

The only essential difference between the Civil transponders and the Military IFF is that the IFF changes "codes" - and probably frequencies - frequently to prevent an enemy from disguising itself as "friendly."

There are apparently trustable reports that the military also uses IFF on ground vehicles, and in COMM devices carried by individual ground units, but I don't know how prevalent that practice is since I haven't been interested enough to look for details.

There are confirmed reports that many military aircraft carry "radar detectors" just like the ones you can put in your automobile (legally in some places). This was a growing practice among pilots who bought their own at the nearest truck stop, prior to orders being placed by the military to purchase them in quantity for large numbers of tactical aircraft. (Since the commercial radar detectors are pretty sloppy about what signals they detect, they were found to be better than existing military stuff for detecting incoming radar controlled weapons. No real help for Sidewinder style stuff though.) One might expect that the FAA will soon require them in commercial civil aircraft if the paranoia continues.

John