While walking with my wife May 19, 2013 in the morning, we heard a prop plane overhead.  My wife turned around and I did too to look upward to try to spot the plane.  I was amazed at viewing an extremely high speed delta wing type of plane with no prop, no windows, no wing or tail flaps, no exhaust, no markings, exceedingly smooth like a dolphin, very pointed nose, white plastic or transparent looking body going west to east over north Orange County California and maneuvering  exceedingly fast with slight corrections which were very rapidly made.  Because this object cut into small puffy clouds I would have to guess it was not a model plane but much large in size.  This object disappeared quickly out of view but the prop sound remained unchanged so I think we failed to spot the plane making the prop noise.  I suspect the flying device my wife and I saw was not the prop plane which means the mysterious “plane” made no noise that we could detect.  At the time, I thought it might be an experimental military craft. I went to the Internet to see if I could find any plane that looked like what we saw but could not find anything.