 The frame side sills are also different; the Alco's are straight from front to rear, while the EMD's step down towards each end of the locomotive.For a long while it was believed that "MRS-1" was an invented railfan name, since it did not appear to have been the official model name in documentation from the USATC or the manufacturers; it was thought to have been derived from "Military Railway Service", the USATC unit that operated them.However, Stefan Nicolaï has found that the designation "MRS-1" appears on the cover of EMD's operating manual for these locomotives, where it appears as "Military Road Switcher MRS-1".