Though intended to be mostly "generic" and wide-ranging, I'm starting off with a rather interesting article/link, from an interesting site, and about an interesting aircraft and it's use.
This Mysterious Military Spy Plane Has Been Flying Circles Over Seattle For Days
Nobody seems to know who specifically the aircraft belongs to or what it's up to, but based on its configuration, its capabilities are pretty clear.
A very unique USAF surveillance aircraft has been flying highly defined circles over Seattle and its various suburbs for nine days now. Nobody at the DoD seems to know who the aircraft belongs to or what exactly it is doing flying so many missions over the Seattle area. But based on its visibly exotic configuration, and information collected by open source flight tracking websites, we can get a good idea of its capabilities and guess as to what it’s up to.
The aircraft, which goes by the callsign “SPUD21” and wears a nondescript flat gray paint job with the only visible markings being a USAF serial on its tail, is a CASA CN-235-300 transport aircraft that has been extensively modified for the surveillance mission. You can see more pictures of the aircraft here
[Thank you Drudge for re-posting this]