Complex sentence: He would later report that as he got closer to the object, he realized it was not an automobile, nor any kind of conventional craft; he thought the object was perhaps some kind of experimental military craft from White Sands Proving Ground not far away.
Split into simpler sentences: He would later report that as he got closer to the object, he realized it was not an automobile, nor any kind of conventional craft. He thought the object was perhaps some kind of experimental military craft from White Sands Proving Ground, not far away.