Starting in 1941, Alco Locomotive Works built 25 of the biggest locomotives that ever lived. The main reason being the Wasatch Mountains, particularly Sherman Hill. This was a stretch of the Union Pacific Railroad's mainline characterized by a continuous, steep 1.55% grade. In order to keep the tonnage moving over the hill, a helper service was a necessity. This was costly. The class 4000s put an end to that. At 6PM on September 5, 1941, the first BigBoy, #4000, was delivered to Omaha. That historical event would be forever engraved in the minds of train BUFFs around the country. From that point on, the biggest and most powerful was achieved.