From the back of the photo:

Official Photograph
Signal Corps U.S. Army
Alaska Communication System
(Credit must be given)
And a typed description, "One of the railmobiles used by the ACS during the war to aid in repairing and maintaining the ACS telegraph and telephone lines along the Alaska Railroad. The ACS no longer possesses any of these vehicles. Sep 1943"

Photo courtesy of the Marv Miller Collection