Comment by dramm

Military aircraft operators in the USA are pretty cautions about non-ADS-B Out or non-transponder operations. Air Force bases etc. will have active MACA (Mid-Air Collision Avoidance) programs, with aircraft and controllers working to reduce conflict potential with civilian traffic. Many bases will have MACA information on their web sites and staff to contact, and they are typically very responsive. Ironically the ones I have worked with were trying to encourage more civilian GA aircraft to adopt transponders, and to utilize the flight following services of their ATC/RAPCON.

TCAS uses active transponder interrogation from the TCAS unit interrogating a threat target's Mode-C or Mode-S transponder. TCAS only uses ADS-B In in an indirect way, in large part to acquire traffic in the area that is not yet a threat, and reduce it's RF congestion caused by excessive interrogation, especially of legacy Mode-C targets. A TCAS II system will fly you right into say a UAT out equipped aircraft without issuing an RA (resolution advisory) if that threat aircraft has no transponder or an inop transponder.

TCAS II only issuing an RA based on active interrogation of a threat aircraft's transponder is a kind of safety feature given the potential spoofing of ADS-B Out data.