(plus Comparing SP Cab-Forward with UP Big-Boy)

Source: https://steamgiants.com/biggest-best-odd/the-largest-steam-locomotives/

If the question is “What’s the largest steam locomotive ever built?”, most people will say it’s the Union Pacific’s “Big Boy”. In fact they are correct, sort of, but not in every category. A few prototypes were larger, but were unsuccessful and either not built or quickly pulled from service.

So, the Big Boy wins for its sheer size, but surprisingly enough is often surpassed in other categories. The Big Boy had plenty of company when it came to being a steam giant. Perhaps the Big Boy comes to mind so easily because of the fame brought by Union Pacific’s own marketing department and of course the recent multi-million-dollar restoration and subsequent Midwest and Western tours of Big Boy 4014.

“Articulated” meant one or more engine units moving independently of the main frame. Articulation allows the operation of locomotives that would otherwise be too large to negotiate a railroad’s curves. Relevant to big steam, Merriam-Webster’s Dictionary defines articulated as: “having a hinge or pivot connection especially to allow negotiation of sharp turns an articulated lorry/bus [or] having sections connected by joints that allow each section to bend or turn independently in different directions” Without the development of the articulated locomotive, railroads would have been forced to limit driving wheels or operate at restricted speeds.

Comparing SP Cab-Forward with UP Big-Boy

Southern Pacific’s Cab Forwards  This unique and highly praised design placed the cab at the front of the locomotive, minus the tender. This arrangement was made possible by burning fuel oil instead of coal. It solved one of the worst fears of being asphyxiated in the many tunnels and snowsheds of the Sierra Nevada’s. Because this locomotive “evolved” several times during the steam era, there were several designations, starting with the AC4 models and ending with the AC12. For simplicity, some of these numbers are not specific.

Whyte Notation: 4-8-8-2
Length (without tender): 79’ – 4”
Weight (without tender): 328.95 tons
Pulling force (tractive effort): 124,300 Lbs
Built: 1937-1942
Builder: Baldwin
Quantity built: 195
Locomotive #’s: 4100 – 4294

Union Pacific’s Big Boy  North America’s biggest successful steam workhorses from the day they were built until the end of the steam era. Several Big Boys are preserved in static displays, with the #4014 restored in 2019 and returned to operational status.

This profile comparison of three articulated locomotives appears in the cab of SP 4294 on display at the California State Railroad Museum in Sacramento. Photo by Chuck Spinks