It was very shiny silver and 2 Army helicopters followed it.

I was waiting for the bus on a Monday.  There were about 6 people with me, but they saw nothing.  I was at 92nd and Greenwood.  As I waited, I looked up at the sky.  I thought I saw a silver bird (seagull).  It was quite far away.  As it came closer, I realized it couldn't be a bird because it was too big.  It was shiny silver and flew slowly towards me.  Then 2 or more (can't remember) Army helicopters (had camophlage paint on them)came behind it.  The craft suddenly dived into some trees and the helicopters followed it.  The people with me were frozen (they didn't talk or move).  Suddenly I said, "Did you see that?"  One of them said what.  I said I think I just saw a UFO.  He said, "Why didn't you tell us when it was here?".
Date is approximate.  PD