Here's an image of USAF 1841 in the Fairbanks yard in July of 1983. The stack is capped, so it looks to be out of service at this date.
US Air Force Locomotive #1841 is a Baldwin S-12 built during the 1950's by Baldwin Locomotive Works. The Baldwin S-1s2 were intended as yard switching locomotive. The Air Force had two in their inventory #1841 and #1842, both are on display at the Museum of Alaska Transportation and Industry in Wasilla, Alaska. The U.S. Air Force used the locomotives at Eielson to transport coal to the generating plant.