bluish-grey oval - very fast , over Hudson River - watched for a long time

Date/time is approximate. It was a clear day, and I was looking out the window of my school's classroom (I was in elementary school at the time).  The school is up on a hill overlooking the Hudson River.  Against the backdrop of the mountains on the other side of the river, I saw a bluish-grey metallic oval object.  It zipped around at very high speeds at various angles, then would pause and shoot off at a different angle.  I watched this object for 15+ minutes, I remember looking at the school clock, as I was starting to get bored watching it (hey, I was a kid).  When I'd finally made up my mind to tell someone else about this, I turned away, turned back to make sure it was still there, and it was gone.
 I am very interested if anyone else saw what I did in June of '75 (or so).  It was the middle of the day, and there were cars going by on the road on the other side of the river.  I can't possibly have been the only one who saw this, yet I have never heard of anyone else who admits to having seen anything unusual that day.
Witness indicates that date of incident is approximate.  PD