I recently bought this watch, which runs well and keeps excellent time. The person I bought it from, who seemed to know something of its history, described it as a President F model dating from 1945 (although the X date marking suggests 1943).
Having looked at the database of watches on this site, it seems to be similar to President models of that period although I'm not sure about the "F" suffix.
The expanding band with which it is fitted has supposedly been with the watch since new. It is marked "Speidel 1945 Phoenix". I would be interested if anyone would know whether this is an original band or not. I must admit, I love the watch but the band looks rather feminine for my taste and I'm not crazy about it, however if it is original I'll stick with it.