The GS-4 runs on four massive 80” drivers, 300lbs psi boiler pressure, and puts out a roaring 5,500 horsepower at 55mph, with a maximum speed of 110 mph. The large drivers gave the locomotive a high top speed; the telling mark of a steam engine built for passenger service. The GS-4 was built for the Southern Pacific Railroad by the Lima Locomotive Works and delivered in the early 1940’s for the SP’s premier passenger trains, finding its way to the Daylight series of name trains. One of the more unique specifications for the GS-4 by the SP was its Mars light, a necessity with the large amount of grade crossings and fog present on the West Coast. The Mars light, like ditch lights on modern locomotives, was utilized as a warning for grade crossings that a high speed train was approaching, its shifting light patterns serving as an eye catcher in foggy conditions.