When I was working on my private pilot license back in 2003 my instructor pointed to unusual aircraft for me, they were always on the apron - had that skunk works grey paint scheme, and just plain looked menacing, which is hard to apply to what they were. One was a Cessna Caravan and the other a Bell Jet Ranger, anyway they had all sorts of antennas protruding from them. Turns out (according to my CFI) that the Caravan flew up and down the I5 corridor scanning and listening to all and every cellphone and general radio transmission. The Jet Ranger flew concentric circles around Portland, again listening to all radio traffic.
Those planes are long gone - but I always wondered if that was true what he said. Anyone have an idea or opinion if that may have been the actual mission for those aircraft ?