551
Built in 1943 by the Baldwin Locomotive Works, Baldwin, Pennsylvania, thousands of the United States Railroad Association Consolidation 2-8-0 type locomotives were assembled in America for war service in England, Europe and Asia.  Outnumbering other war-time railroad engines, they were simple to maintain with the close clearance required for the narrow bridges and tunnels on European railroads.
Instead of being shipped to Europe, twelve of these locomotives were sent to Alaska by the U.S. Army to become Alaska Railroad Class 550.  All twelve locomotives saw service over the 460 miles of the Alaska Railroad.
The photo shows number 551 and south-bound passenger at the Anchorage Depot on May 13, 1949.

 
Alaska Railroad photo, Jack Klingbeil collection