A cover from 1957

I mentioned a couple posts back that I've got an RPO cover that was canceled on March 4. I actually have a couple of them, so here's one of them...

At first glance, there isn't very much remarkable about this cover.  There is some dirt smudging around the stamp, it's a rather common U.S. commemorative stamp, there's a ghost of another cancellation in the address area (my guess is that this is from traveling through an automated canceling machine), and the cover itself is unaddressed.  The cancellation was made aboard train 1 on the Jacksonville and Pensacola RPO route on March 4, 1957.  Since I haven't researched RPOs as much yet (which seems odd when you consider that one of my other websites is all about trains and model railroading), so I don't know the significance of the "E.D." in the route name.  The back of this cover gives another small clue as to this cover's travels.

The back stamp shows that the cover was received in Dothan, Alabama, at 10:30 am, on March 5, 1957.  The cover flap is intact and appears as if it was never sealed.  That and the fact that this is an unaddressed cover leads me to believe that it was created by someone who wanted this specific RPO cancellation.  Now it's part of my March 4 collection.