A 2-8-8-8-4, probably from the Chesapeake & Ohio railway, or the Baltimore & Ohio, or the Norfolk & Western, or the Western Maryland. I don't believe it came into frequent use, and was actually cut in half to make two smaller, more practical locomotives.
For some reason, the four abovementioned roads tried elephantine locomotives, and some of them actually worked, but I've always been mystified.
The Union Pacific's 4-8-8-4 had the straightaway and generally level terrain of Nebraska and eastern Wyoming (where they were used) on which to run. It's been a very long time since I've seen the mountains of Virginia, Maryland, and West Virginia, but I remember them as looking somewhat too daunting for large locomotives, but somehow these four eastern roads found
some big models usable.