EMD F7

The EMD F7 entered production in February 1949 as the fourth generation of General Motors' Electro-Motive Division's highly successful F-unit cab locomotive series. It succeeded the F3 and would later be followed by the F9, with the numbering chosen to align with the contemporary E7 passenger locomotive rather than to indicate any sequential count of F-unit models. Final assembly took place at EMD's facility in La Grange, Illinois, and at the General Motors Diesel plant in London, Ontario, which handled units destined for Canadian railroads. Production continued through December 1953, during which time EMD built a total of 2,366 units across A and B configurations, making the F7 not only the best-selling cab unit in North American railroad history but reportedly the most numerous F-unit model by a considerable margin. Approximately fifty railroads acquired F7 units during the production run. The Southern Pacific Railroad was the single largest purchaser, taking delivery of 294 cab-equipped A units and 236 cabless booster B units. Other significant buyers included the Atchison, Topeka and Santa Fe Railway, the New York Central Railroad, the Baltimore and Ohio Railroad, and the Pennsylvania Railroad. Canadian National Railway and Canadian Pacific Railway received locomotives built by GMD, taking 76 and 29 units respectively. Although marketed primarily for freight service, the F7 proved versatile enough for passenger operations as well, and units saw service on named passenger trains including the Santa Fe's Super Chief and El Capitan. The F7's legacy extended well beyond its production years, as many units remained in active service for decades owing to their reliability and relatively economical maintenance requirements. The Santa Fe undertook one of the more extensive rebuilding programs, converting approximately 190 of its F7A units into CF7 hood-style road switchers during the 1970s. Other units were rebuilt by Morrison-Knudsen into F9PH configurations for passenger service, and additional rebuilds served the Massachusetts Bay Transportation Authority as commuter rail locomotives. Several examples survive today at museums and tourist railroads across North America, with at least one unit maintained in operational condition at the California State Railroad Museum in Sacramento.

The F7 was powered by EMD's 567B series prime mover, a 16-cylinder, two-stroke diesel engine arranged in a 45-degree V configuration, producing 1,500 horsepower at 800 rpm. Each cylinder displaced 567 cubic inches, yielding a total engine displacement of approximately 9,072 cubic inches. The engine drove a direct-current generator mechanically coupled to the flywheel end of the crankshaft, which in turn supplied current to four nose-suspended DC traction motors. The motors were mounted in pairs on Blomberg B trucks, giving the locomotive a B-B wheel arrangement. One of the most significant performance improvements over the preceding F3 was a roughly 20 percent increase in continuous tractive effort, with a standard F7 equipped with 65 mph gearing rated at 40,000 pounds of continuous tractive effort compared to approximately 32,500 pounds for an equivalently geared F3. Externally, the F7 was difficult to distinguish from late-production F3 units, as the primary differences between the two models were internal electrical system changes rather than major mechanical or structural alterations. One reliable visual indicator is the absence on all F7s of the wire mesh grille panels colloquially known as chicken wire grilles, which appeared on most F3 carbodies. The F7 can be distinguished from the later F9 by the number of carbody center louver groups: F7s have four such groupings, while F9s have five, with the additional louver group positioned ahead of the forward porthole. Units were produced in both freight and passenger configurations, with passenger variants typically equipped with dual headlights, though considerable variation existed across individual orders and railroads.

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