The C-12 Huron is the military version of the King Air.  While it has been successful as a transport, it has also been the basis for a ton of derivatives.  I am not an expert on this type and all of its subtypes so, when I see one, I can’t say for sure what it is.  The most recent versions have been the MC-12W but I am not sure that they all look alike.  When I saw this plane taxiing out at Boeing Field, I wondered if it was an MC-12W and asked a couple of friends that know more than me.  They weren’t sure either.  It might be or it could be something else.  Whatever it is, it was an unusual visitor.