The 4-8-8-4 wheel arrangment was unique to both the United States and to the Union Pacific Railroad. No other railroad and no other country made locomotives anything like these.
Many consider the 4-8-8-4s or "Big Boys" to be the largest steam locomotives ever built in the entire world. It would be hard to argue differently.
When the Union Pacific created plans to have a locomotive designed that could haul 3,600 ton trains unassisted over the Wahsatch Mountains east of Ogden, UT, they had plans to give the name "Wahsatch" to this wheel arrangement. However, during the construction of the first of these locomotives, an ALCO machinist wrote the words "Big Boy" on the smokebox of the locomotive. The name stuck and became the name of this locomotive type.
ALCO built 25 of these locomotives for the Union Pacific at a cost of about $265,000 each. Based on inflation, the equivalent amount of money in 2018 would be $4,700,000 per locomotive.
If you were to ignore all of the unsuccessful and experimental locomotives, then look at the overall ratings of the remaining steam locomotives in the above categories, it would become clear that there were many large locomotives. One could argue that the Big Boys were the largest and maybe they were. But the NP Z-5, the DM&IR M-3/4, the C&O H-8, and the N&W Y6b were all examples of the largest of all successful steam locomotives.
|Railroad||WP||N&W||GN||NP||SP||DM&IR||B&O||SP||UP||UP||C&O||N&W||PRR||PRR||South African Railways|
|Class||M-137||Y6b||R-2||Z-5||AC-9||M-3/M-4||EM-1||AC-10/11/12||Big Boy (4884-2)||4664-5||H-8 - 1600||A||Q2||S1||GL|
|Cyl:Dia x Stroke||26x32||25x32||28x32||26x32||24x32||26x32||24x32||24x32||23.75x32||21x32||22.5x33||24x30||19.75x28||22x26||22x26|
|Evaporative Heating Surface||6,811||4,915||7,869||7,673||6,918||6,782||5,298||6,470||5,755||4,642||7,240||6,639||6,725||5,661||3,396|
|Superheater Heating Surface||2,152||1,478||3,515||3,219||2,831||2,770||2,118||2,616||2,043||1,741||3,186||2,703||2,930||2,085||835|
|Weight on Drivers||552,700||548,500||544,000||558,900||531,200||560,257||485,000||531,700||545,200||404,200||507,900||432,350||393,000||281,440||324,464|
|Total Engine Weight||665,100||611,520||630,750||723,400||689,900||695,040||628,700||657,900||772,250||634,500||771,300||573,000||619,100||608,170|
|Maximum Axle Weight||69,088||68,000||70,900||66,400||62,100||69,100||67,800||86,700||72,000||79,780||40,992|
|Total Engine and Tender Weight||1,073,350||990,120||1,003,530||1,125,400||1,090,600||1,133,040||1,010,700||1,051,200||1,208,750||1,069,000||1,199,400||951,600||1,041,100||1,060,010||472,864|
|Tractive Effort Booster||13,900||13,400||15,000|
|Drawbar Horsepower||5,600@25||6,000@403||6,firstname.lastname@example.org||7,498@46 (#1608)||6,300@452||7,200|
|No.||Class||F.M. Whyte||Gauge||Railroad Line||Location||Status||Builder Info||Notes|
|4014||48841||4-8-8-4||4'-8½"||UP||UP engine house, Cheyenne, WY||operational||Alco (Schenectady) #69585, 11/1941||From Pomona, CA. Reacquired by the Union Pacific in July 2013. Restored to operation on May 1, 2019. Converted to burn oil. Temporarily uses the tender of UP 3985. Became the first-ever steam locomotive to be equipped with Positive Train Control.|
|4004||48841||4-8-8-4||4'-8½"||UP||US 30, Holliday Park, Cheyenne, WY||display||Alco (Schenectady) #69575, 09/1941|
|4005||48841||4-8-8-4||4'-8½"||UP||Forney Transportation Museum, Denver, CO||display||Alco (Schenectady) #69576, 10/1941||First UP Big Boy to be converted to burn oil before UP 4014. Converted back to burn coal in March 1948. Only UP Big Boy to be involved in an accident.|
|4018||48841||4-8-8-4||4'-8½"||UP||Museum of the American Railroad, Frisco, TX||display||Alco (Schenectady) #69589, 01/1942||Displayed with UP Centennial 6913.|
|4017||48841||4-8-8-4||4'-8½"||UP||National Railroad Museum, Green Bay, WI||display||Alco (Schenectady) #69588, 01/1942||Displayed with PPR GG1 4890.|
|4023||48842||4-8-8-4||4'-8½"||UP||Lauritzen Gardens, Omaha, NE||display||Alco (Schenectady) #72780, 11/1944||Displayed with UP Centennial 6900.|
|4012||48841||4-8-8-4||4'-8½"||UP||Steamtown National Historic Site, Scranton, PA||display||Alco (Schenectady) #69583, 11/1941||Underwent a cosmetic restoration between 2019 and 2021.|
|4006||48841||4-8-8-4||4'-8½"||UP||Museum of Transportation, St. Louis, MO||display||Alco (Schenectady) #69577, 10/1941||Displayed with UP Centennial 6944.|