Big Boy was a massive steel locomotive weighing 1,250,000 pounds, or 612.5 tons with its tender included. The American Locomotive Company built 25 of these locomotives for the Union Pacific Railroad between 1941 and 1944 to pull mile-long freight trains through the Wasatch Range from Ogden, Utah, to Green River, Wyoming. Along a route where most grades reached .82% and one stretch rose to 1.14%, earlier 3900-ton trains had required two large locomotives coupled together, but Big Boys were designed to haul even heavier trains with a single locomotive. Working with ALCO, the Union Pacific design team created a 4-8-8-4 wheel arrangement, with four leading wheels, two separate sets of eight driving wheels, and four trailing wheels for stability. With twenty-four wheels in all, it was the largest and most powerful coal-fired locomotive ever built, capable of hauling a 7900-ton freight train through the Wasatch at over 60 mph. As steam locomotives gave way to diesel in the early 1950s, Big Boy's service neared its end, and its last commercial run came on July 21 1959. The Big Boy built in Schenectady remains the largest locomotive the world has ever known.