The EMD SW1 is a 600-horsepower (450 kW) diesel-electricswitcherlocomotive 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 3,402 cu in (55.75 L) 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 600 hp (450 kW) V6 form. 661 locomotives of this design were built, not withstanding diesel switcher production having been suspended between 1942 and 1945 by the War Production Board, as the 567 engines were needed elsewhere, mainly for U.S. NavyLST vessels.
The SW1 introduced a 6 cylinder version of the 567 (later 567A) series engine to EMC/EMD switchers. Developing 600-horsepower (450 kW) 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 81⁄2 by 10 in (216 by 254 mm), bore by stroke, giving 567 cubic inches (9.29 L) 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, use the AARType A switcher truck. EMC/ EMD has built all its own components since 1939.
Like most long-running locomotive models, a number of changes were made to the SW1 over its production life. Internally, the post-1945 locomotives were somewhat improved, and used an updated 567A engine.
One easily spotted change is the shape of the two center cab windows over the hood, which were curved to follow the roofline originally, but became flat-topped after mid-1950. Another easily seen 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 switcher stack, while early units were generally modified with taller stacks too. Early locomotives had a single large headlight, while later had twin sealed-beam headlights.
The SW1 appears very similar to its SC and SW predecessors, but has only a single stack instead of two, a significantly shorter hood and a larger rear platform, no small louvers on the front top hood sides, and a large grille instead of lifting vents on top of the hood front. The sandbox in front of the radiator is somewhat smaller on the SW1.
Compared to later EMD switchers, the SW1 has a much shorter hood, large platforms at each end, a single exhaust stack, and a large 'satchel' type sandbox.