NATO aircraft assigned to the Baltic Air Policing mission regularly intercept Russian aircraft when they don’t use transponders to identify themselves or fail to respond to hails from air traffic controllers, meaning they appear on radar simply as an unidentified contact.
The Baltic Air Policing mission is led from Šiauliai Air Base in Lithuania, where the Spanish and Portuguese Air Forces currently have fighters deployed. An additional nation usually covers the Baltic Sea from Ämari Air Base in Estonia, but fighters are temporarily stationed in Latvia while the Estonian Air Force improves the runway.