4015 was officially a model FA-1 1500 hp A unit which along with its B unit cabless version were known by "covered wagons" because access to their engine rooms was covered, thus weather protected, something appreciated by engine crews. One of twenty MLW A units (20 B units) and 8 Alco A units (4 B units), all were later upgraded to 1600 hp. MLW #77310 8/50 Most were traded in to MLW on an order for 51 Century C-424 2400 hp road switchers numbered in 4200 series.