The rarely seen S-4 class of Canadian National 2-8-2s is represented here by No. 3801, in this CNR publicity photo acquired through Rail Photo Service of Boston. The prototype S-4-a engine, No. 3800, was built by the Canadian National shops in 1930 and was followed by Nos. 3801-3805, of class S-4-b, erected by Canadian Locomotive Company in 1936. (One source claims there were ten locomotives in all, but two other sources list only six.) No. 3801's group had 63-inch drivers, 24x30-inch cylinders, and 265 p.s.i. of boiler pressure. They had 3404 square feet of evaporative heating surface and a superheater surface of 1452 square feet. With an engine weight of 339,000 pounds, they developed 60,615 pounds of tractive effort. The S-4 Mikados featured special appliances designed to reduce boiler foaming caused by hard water in the western Canadian prairies; the unusual skyline casing visible on No. 3801 hides that equipment. This engine was renumbered to 4093 in June 1956.