On the outside looking in - no doubt I had the same reaction that
Jon Wright had upon discovery that a favorite locomotive had been moved outdoors, behind the closed doors of the North Machine Shop at the B&O Railroad Museum. This streamline 4-6-4 Hudson, know also as a "Yellow Belly" (a full view can be seen here) actually started out as a 4-6-2 Pacific and was built by Alco way back in 1926.
"Shortly after the end of the war, in 1946, the C&O decided to upgrade their passenger service. The C&O was primarily a coal-hauler and therefore wanted to improve steam locomotive technology. They developed a new luxury liner between Washington and Cincinnati named the "Chessie." The new liner was to be powered by experimental steam-turbine-electric locomotives. In addition, the C&O's Huntington shops rebuilt the No. 490 and the other 4-6-2s into 4-6-4 "Hudsons." The new locomotives had roller bearings, front-end throttle, high-speed booster, cross counterbalance, and the Franklin system of steam distribution." - from the B&O Railroad Museum's web site.