ex-Southern Pacific 3100
U25B number 3100 represents a very early configuration of the four-axle GE road switcher (six-axle models were always sold alongside, with minimal changes.) As production continued, the single-piece windshield gave way to a two-pane unit owing to the high cost of replacing it when it was damaged. The cab moved forward on the frame, shortening the nose. The radiators grew significantly as horsepower increased, causing protruding "wing" extensions to sprout from the end of the long hood. Finally, when the U-series gave way to the "Dash 7" in the 1970s, a new "floating-bolster" truck design eventually replaced the AAR Type B trucks seen here, although that is a highly variable detail in any case owing to the reuse of traded-in trucks from older locomotives.
ex-Southern Pacific 3100
U25B number 3100 represents a very early configuration of the four-axle GE road switcher (six-axle models were always sold alongside, with minimal changes.) As production continued, the single-piece windshield gave way to a two-pane unit owing to the high cost of replacing it when it was damaged. The cab moved forward on the frame, shortening the nose. The radiators grew significantly as horsepower increased, causing protruding "wing" extensions to sprout from the end of the long hood. Finally, when the U-series gave way to the "Dash 7" in the 1970s, a new "floating-bolster" truck design eventually replaced the AAR Type B trucks seen here, although that is a highly variable detail in any case owing to the reuse of traded-in trucks from older locomotives.