Class CR-12b Series #1615-1617 (ex-#7615-7618), built 1951:

Canadian National Railways had previously purchased H10-64s (CR-12a, CRG-12b), unique to Canada in being built with A-1-A trucks. This permitted the reduced axle loadings suitable for branch line service. In 1951 and 1952, the CNR uprated eighteen H10-64s to 1200 h.p. H12-64s and in 1952-53 took delivery of twelve higher horsepower H12-64 units (CR-12c and CR-12d).

All of these locomotives were built by Canadian Locomotive Co. in their Kingston facility. These units were built with Train Master-style carbodies and were 56'4" over couplers. Originaly numbered in the 7600-7629 series, the H12-64s were later renumbered 1600-1629.