The story of dieselization on the Reading began in 1926 with the purchase of a 300 horsepower boxcab switcher, the second diesel locomotive in regular service in America. 62 more switchers would be acquired over the next twenty years before the first road freight units joined the roster. These units were ten FT A-B sets. In 1948, six F-3A?s, numbers 260A - 265A and 6 F-3B?s, numbers 260B - 265B, were purchased as three 4 unit, 6,000 horsepower locomotives for the Shamokin Division. But 6,000 horsepower was too much and the units were split into two 4,500 horsepower and three 3,000 horsepower sets. In 1950, eighteen F-7A?s 266A ? 283A and six F-7B?s, numbered 266B ? 271B, were purchased as class DF-4. They were formed into six 4,500 horsepower A-B-A sets for the Shamokin Division and six A-A sets for the Reading Division. The F-3?s, operating as six A-B sets, soon joined the F-7?s on the Reading Division. The Athearn Genesis Reading units are F-3A 262A and F-3B 262B, built in 11/48 as EMD builder?s numbers 6184 and 6190, F-7A 267A and F-7B 267B, built in 5/50 as EMD builder?s number 9803 and 9821 respectively, and F-7A 274A, also built in 5/50 as builder?s number 9810.