The EMD SW1 is a diesel-electric switcher locomotive built by General Motors' Electro-Motive Corporation (later Division) between December 1938 and November 1953. Final assembly was at EMD's plant at LaGrange (McCook) Illinois. The SW1 was the second generation of switcher from EMD, succeeding the SC (cast frame) and SW (welded frame). The most significant change from those earlier models was the use of an engine of EMD's own design, the then-new 567 engine, here in V6 form. 661 locomotives of this design were built, with a gap in production between March 1943 and September 1945 due to World War II. The SW1 was the start of a long line of SW series switchers produced by EMD. It was complemented by the SW7 in 1949 and the SW8 in 1950. SW1 production ceased in November 1953, with its replacement, the equally powerful SW600, starting production in February 1954. Locomotive name EMD arrived at the name SW1 based on the locomotive's power (S for 600 hp) and frame design (W for welded), and the number 1 was added to distinguish the new design from the previous EMD SW. As new and more powerful SW designs emerged in the 1950s, the SW name evolved to instead stand for "switcher." Engine and powertrain The SW1 introduced a 6-cylinder version of the 567 (later 567A) series engine to EMC/EMD switchers. Developing at 800 rpm, this engine remained in production until 1966. Designed specifically for railroad locomotives, this was a supercharged 2 stroke 45 degree V type, with an , bore by stroke, giving displacement per cylinder. A D.C. generator provides power to four motors, two on each truck, in a B-B arrangement. The SW1, like most EMD switchers, uses the AAR type A switcher truck. EMC/EMD had built all its components since 1939. Production changes Several changes were made to the SW1 over its production life. Internally, the post-war locomotives used the 567A engine. Externally, the two center cab windows over the hood, which were curved to follow the roofline originally, became flat-topped after mid-1950. Another external difference is the taper of the hood to the cab, which was a two-stage taper in earlier units but became a single taper in later production. Very early locomotives were delivered with a stubby exhaust stack, but this did not lift the diesel exhaust sufficiently clear of crew visibility. All later units were delivered with EMD's standard conical