huge, diamond shape object flying low in southern Maine

This happened approximately 28 years ago.  I did not report it.  I do so now because the UFO sightings I've seen on television have been disappointing.  
My daughter and I stepped out of our home in  daylight.  We saw an enormous craft, perhaps 3 football fields long come out of the east at a low altitude and pass over our heads. 
This immense craft then disappeared to the west.  It was diamond shape, and I could see details on the underside as it passed overhead.  
Over the years sightings expanded from the saucer or ball shapes to include triangle UFO's, but the UFO I sighted did something that as far as I know has never been reported.  It flew with the base of the triangle forward, not point forward.
Witness indicates that the date of the incident is approximate.  PD