Number 1050 is an Alco RF1A.  It was built in 1943 (builder #70661) for the U.S. Army, #8040.  The Alaska Railroad purchased it in 1947.  It was their first streamliner and made its shakedown run to Palmer and back on October 16, 1947 with a trainload of school children.  On October 18, formal ceremonies were held at the Anchorage Depot prior to its run north for the first Alaska Day celebration at the Mount McKinley Park Hotel.  Locomotive 6 (renumbered to 1 for aesthetic reasons) was also on hand to provide a contrast between the old and the new.  A military band played music and the streamliner was christened the "AuRoRa."
In the photo above, ARR General Manager Colonel J.P. Johnson (second from left) hold "Moose Gooser (a nickname for Alaska Railroad locomotives) with several guests.

Alaska Railroad photo from the Jack Klingbeil collection