Ed. That is the last GE U23B ever produced (P&W 2203). The RMNE was able to acquire it from the P&W (hence the paint scheme). It was previously known as Conrail # 2798.
The NR stands for Naugatuck Railroad. The Railway Museum of New England, (RMNE) based in Thomaston, CT, is using it as additional power in its roster. We acquired it due to the historical significance of it being the very last U23B to roll off the production lines. We also have the last U25B purchased by the New Haven (#2525).
Eric