The MLW RS-18 was the successor to the 1,600hp 244-powered RS-10 which proved to be somewhat unreliable. There were no such issues with the 1,800hp RS-18, with its 12-cylinder model 251B diesel engine, and it is widely considered to be MLWs most successful product from both an operational and a mechanical point of view.
Based on the Alco RS-11, the Canadian-specific RS-18 (which MLW designated DL-718) was alike in most aspects externally and internally except for the notchless hood ends. Montreal Locomotive Works constructed 351 RS-18s between December 1956 and June 1968 for eight railways including Canadian National (225), Canadian Pacific (72), Pacific Great Eastern (29), and 25 for smaller railways. The RS-18 was available in both “standard” and “lightweight” versions, which usually, but not always, rode on standard 9’-4” wheelbase AAR type B trucks or special lightweight trucks respectively. CN acquired examples of both (131 standard versus 94 lightweight units).