In late 1954 MLW introduced the RS-10 which had the same 12 cylinder 244 engine as the RS-3 but in a radically altered carbody with a much higher hood. The hood was almost level with the cab roof and gave more space for additional equipment such as dynamic brakes and steam generators. It had a more angular appearance with flat ends (rounded where they joined the sides), a feather-edge hood peak, two angled number boards (with sand-box lids below) on each end and a prominent intercooler covered with a grille just behind the radiator shutters. As built, there were two layouts for the carbody filters. Units without dynamic brakes, or with dynamic brakes in the short hood, had three square carbody filters in a horizontal line close to the intercooler (see the photos of 3818 in green and yellow livery — it had dynamic brakes in the short hood and so had the extra louvers on the left hand side of the short hood). Units with dynamic brakes in the long hood had the three square carbody filters plus two closely spaced filters near the cab (see photo of 3091 which has dynamic brakes in the long hood). In 1955 when CN purchased more 1600 hp road switchers they acquired the RS-10/RS-10S model and over the next three years bought a total of 51 units. The first 15 units had Amplidyne excitation (RS-10) but subsequent units had the more reliable Static excitation and were designated model RS-10S. The RS-10/RS-10S was unique to Canada and was purchased by CN, CP, ON and PGE.
The first units (model RS-10) were numbered 1863-1885 (MR-16e, f, g, h) and then in 1956 renumbered to 3043-3065 (in 1957, 3043-3057 became 3800-3814). The next units (MR-16j, k) were model RS10S and were numbered 3066-3093 (later, 3066-3073 were renumbered 3815-3822). None had steam generators.
The 3800-number series was created to identify units that were lightweight (228,000 pounds) and rode on lightweight MLW trucks (no prominent lateral leaf spring). Of these, 3807-3822 had dynamic brakes in the short hood. By contrast, units 3058-3093 weighed between 243 and 245 thousand pounds and of these 3058-3060 and 3074-3093 had dynamic brakes in the long hood. More information can be found in the article by Ken Goslett in Railroad Model Craftsman August 1994 pages 55-57.
Canadian National changed the layout of carbody air-filters and some units even had different layouts on each side!. Eventually most, if not all, units received the standard layout applied to the RS18 units (see later section) as shown in the photo of 3818 in its final years in the black and orange livery. All units had been retired by 1970.