I'll have to check my latest roster, but I believe the base is limited to GE 80-ton centercabs. There was an Alco S1 on the roster, probably the last one in the entire DOD inventory, but it may be gone by now. I should know for certain later this year when I visit the base. Check this website for a roster of DOD base locomotives:
Note: The webmaster is currently updating the page, as some of it is clearly outdated. For example, the tracks to the naval base at Indian Head, MD, were torn up several years ago, and the Army Reserve's 1205th TROB was inactivated in Sep 06. Its two GP10s went to the Tennessee Valley Authority. Generally speaking, though, it's a good source of roster information.