The EMD SW7 was the third diesel locomotive switcher the builder produced in the SW series and the first new design following World War II in the late 1940s (EMD halted production and development on new models until after the war, mostly due to war restrictions ongoing at the time). Outwardly, the SW7 was virtually identical to future SW models and related NW designs of the time although it did differ slightly from the earlier SW1 in that it featured a more streamlined hood without the "step" in front of the nose. The most striking difference between the SW1 and SW7 was the latter's additional horsepower, which was twice that of the former. As with many early EMD switcher locomotive models the SW7 continues to see use today in many various settings from industrial and shortline operations to tourist and excursion trains. There are currently two models officially known to be preserved (CB&Q #9255 at the Illinois Railway Museum and Southern #8202 at the Southeastern Railway Museum) although more are sure to follow as they are retired from freight service.
The EMD SW7 debuted in October, 1949 and looked to follow the success of the previous SW1 and NW2 models, which combined, sold more than 1,800 units between 1939 and 1953. The history of the SW line, of course, dates back to the Electro-Motive Corporation of the mid-1930s which began releasing a whole series of small switchers for use in light duty and industrial work. They almost instantly became successful and after the company became a division of General Motors it continued to expand on the series. In any event, all EMD switcher locomotives after the SW7 are very hard to tell apart. The SW7 used the traditional EMC/EMD carbody design, that was tapered near the cab and featured EMD's classic conical exhaust stacks above the hood. Length remained the same at just over 44-feet and it continued to use GM's model D37 traction motors.
The biggest difference, to date, with the EMD SW7 over any previous model was simply horsepower. Using the updated V12 567A prime mover the SW7 could produce a hefty 1,200 horsepower for such a small switcher of its size (almost a tug boat on steel wheels!), and produced 36,000 pounds of continuous tractive effort and 62,000 pounds starting. Overall, the locomotive weighed just 124 tons and remained about 44 feet in length. Also, by the time the SW7 was developed the "SW" designation EMC originally used, which stood for six-hundred horsepower, welded frame had long since been dropped with EMD simply having refer to "switcher."
Once again, railroads were impressed and orders for the SW7 quickly began to pile up. As with previous models the SW7 was meant to be used in yard, light branch, and industrial settings which also helped in finding many buyers. With a very reasonable price tag some 489 SW7s were produced in less than a two year time span, through January, 1951. The roads to purchase the SW7 are far too numerous to mention here. However, some of the industries to purchase the locomotive included Weyerhaueser Timber Company and the Phelps Dodge Corporation. It should noted that EMD also produced another cow/calf version of the SW7 known as the TR4. This model sold 15 total sets to the Santa Fe, Belt Railway of Chicago, Chesapeake & Ohio, and Milwaukee Road.
Just as with previous EMC/EMD switcher locomotive designs of the time, it's somewhat amazing that several SW7s remain in use in all types of applications from industrial to shortline settings more than 60 years since the last one rolled out of the assembly line. Places were you can still find the SW7 in operation include the Conemaugh & Black Lick, Lehigh Valley Rail Management, Mansbach Metal Company, Independent Locomotive Service, Midwest Steel and Alloy, Turtle Creek Industrial, Chicago-Chemung Railroad Company, Heritage Railroad, J&L Consulting, New York New Jersey Rail, Seaview Railroad, Peoria and Pekin Union Railway, STRATA Corporation, and the Chesapeake Auto Terminal, Inc. You can also find many preserved at museums, as mentioned above, and because of their ease of maintenance several also are used in excursion train service.