This N Scale Kato 4-8-8-4 Big Boy is based on the huge Union Pacific steam locomotive restored for operation in honor of the railroad's 150th anniversary. The 4-8-8-4 Big Boy is an articulated Steam Engine manufactured by the American Locomotive Company between 1941 and 1944. The Union Pacific was the sole purchaser of these engines, owning and operating a total of 25 of the colossal 600 ton engines. The 4-8-8-4 wheel arrangement combined stability and power, with the four wheel leading truck allowing for smoother entry into curves while the two sets of 8 drive wheels provided 135,375lbs of tractive force. The trailing four-axle truck helped support the large firebox that was needed to keep the massive engine fed. The original Big Boy engines were coal powered, with 4014 being converted to oil when it was rebuilt after its retirement to be used in excursions.