Large object on a clear day completely vanished after hovering in plain sight

Summer of 1968 driving down Broadway Terrace out of Oakland Hills, road becomes a large boulevard, in a convertible unobstructed view, crest a hill clear view of San Francisco Bay I look up out over water, hovering is a large brown cigar shaped mass, no sound, 
my husband sees it also, we pull over to look, another gentlemen stops to look, the usual exchanges ie' What is it? Why doesn't every else look up? etc.  There is no doubt it has mass and weight and completely stationary, I think I see windows, but that is impossible, it's must be something secret from the government, what else could it be?  
It hovers a rather long time, maybe more than 3 minutes, then it is completely and silently gone.  No trail, nothing just gone. The next day my husband reads in the Oakland Tribune a policeman say something hovering over the bay at about the same time.  We never, ever reported it.