Kinda old great video though! It's over lapping of copper and silver/steal I think that bends the light I remember watching a documentary on this. There was a rumor that they did this with a Tank to win a major US battle I'll try to find the link.
"There is the infamous story from October 28th, 1943, in which the U.S.S. Eldridge, a destroyer escort, was reputedly rendered invisible to the naked eye for a few brief moments, in what has been dubbed the Philadelphia Experiment."