"How to Track the U.S. Air Force’s Secretive Commando Planes"

WIB:

The Pentagon doesn’t have to register its planes and choppers with the FAA. However, commandos can try and keep a lower profile in turbulent regions by flying aircraft with a civilian-style paint and civil registration codes. When the N numbers aren’t necessary, the Air Force planes simply display their military serial numbers.

And with that data, you can easily track these aircraft on the web. When not on a mission, the commandos fly with their transponders active for safety reasons.