This nice tribute to the Gray Eagles (WWII pilots) was in conjunction with an air show in Ohio called "The Final Roundup." It was the last large gathering of the remaining P-51 Mustang fighters used during WWII. There were about 120 of the fighters there -- all of them in flying condition, of course. The flyover seen at the end of the video is compose entirely of P51s spelling out the number 51. It was an event that may never be seen again.

http://www.grayeagles.org/video.htm