Railroads & Locomotives Locomotives Largest 2-10-0 Decapod fleet: Pennsy’s I1 ‘Hippos’

Largest 2-10-0 Decapod fleet: Pennsy’s I1 ‘Hippos’

By Kevin P. Keefe | March 1, 2023

With 598 locomotives, the I1 was the road’s standard freight hauler

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The railroad with the largest 2-10-0 Decapod fleet should come as no surprise.


Throughout most of its history, the Pennsylvania Railroad called itself “The Standard Railroad of the World,” and yet in so many ways it was anything but “standard.” From position-light signals along its right-of-way to Belpaire boilers for its steam locomotives to its use of 155-pound rail, the Pennsy was, in actual fact, a nonconformist. That approach was obvious in its approach to the kind of steam power it chose, never more so than its embrace of the 2-10-0 Decapod.


The Decapod has a curious history in the U.S. A light version of the wheel arrangement began appearing on American railroads in the late 19th century and was often an effective tool in branch-line service, but by the eve of World War I the type was largely considered obsolete. More than 200 American 2-10-0s built for Russia (part of an order for 1,200) were diverted to domestic railroads on account of the Bolshevik Revolution, and they proved successful, but the engine’s long wheelbase and correspondingly small firebox caused most railroads to opt for the 2-8-0 Consolidation or the 2-8-2 Mikado.


The big exception, of course, was the Pennsy. Other major Eastern coal haulers — Baltimore & Ohio, Chesapeake & Ohio, Norfolk & Western for example — had largely gone with the 2-8-8-2 as standard drag power. But in 1916 the PRR went against conventional wisdom and began building its first group of what it classified as the I1s 2-10-0 at its Juniata Shops in Altoona, Pa., a total of 123 locomotives; the “s” was for superheated, something worth specifically noting in that era. The introduction of a new PRR engine was big news in Altoona — the headline in the Nov. 20, 1916, edition of the Altoona Tribune read “Monster Steam Locomotive is Turned Out From Juniata Shop.”


Steam locomotive in profile
PRR 4644, a member of the largest 2-10-0 Decapod fleet, rests at Williamsport, Pa., in September 1955. Don Wood photo


Morgan weighs in on the I1


What followed in quick succession was astounding: the gradual accumulation of 598 Decapods, including 475 from PRR’s stalwart supplier Baldwin. This cemented their status as the largest 2-10-0 Decapod fleet. The I1 became the standard PRR freight hauler. The sheer size of the fleet caught the attention of longtime Trains Editor David P. Morgan.


“What gutty machines they were and what a chapter in the history of the American steam locomotive,” wrote Morgan. “For example, those who think of standardization in steam in terms of 275 New York Central Hudsons (albeit in three distinct classes) or even 425 alike Pennsy K4 Pacifics might ponder the fact that the original experimental I1 came out of Altoona in December 1916, was quickly followed by 122 homemade sisters, and — just as soon as the U.S.R.A. had passed — multiplied into an order for 100 from Baldwin in 1922 and 375 more in 1923! Imagine it — 598 locomotives of a single class of a single wheel arrangement on a single railroad. Why, that number is a tenth of all the steam power operated by a big road like L&N in its lifetime . . . or more than the total of all the 2-8-2s, 2-8-4s, 4-6-4s, and 4-8-2s that Santa Fe ever operated!”


The I1 engines came to be called “Hippos,” a reference to their fat boilers squatting on relatively small 62-inch drivers. The I1 was big, almost unbelievably so for its era. Its boiler pressure was a whopping 250 psi, still employed relatively rarely, and it delivered to the rail approximately 90,000 pounds of tractive force. Its 22-foot, 8-inch driving-wheel base necessitated the use of flanges on only the first and fifth set of driving wheels; curves in PRR coal country called for mostly “blind” drivers on an engine as long as the I1. And that extra-long running gear restricted the size of the firebox to only 69.9 square feet, making life difficult for any fireman required to keep the I1’s massive 30½ -by-32-inch cylinders fed with steam. Its running gear was equally bulky, with 11-foot, 1½-inch main rods, 8 ½ inches thick at the crankpin. (The largest 2-10-0s, however, at least by weight on drivers, were Western Maryland’s I-class machines).


Two steam locomotives lead a train through a city
An ore train hammers through the center of the hillside mining town of Shamokin, Pa., with two I1 2-10-0 Decapods up front on Sept. 14, 1956. Philip R. Hastings photo


Upgrades for the largest 2-10-0 Decapod fleet


The PRR Hippos began to undergo upgrades in 1930 as the I1sa, after which most of the class received modifications of the valve gear that, among other advantages, boosted average tractive force to 96,000 pounds. Originally equipped with PRR’s screaming Banshee whistles, some lasted long enough to receive K4 whistles and, more importantly, huge 21,000-gallon tenders, along with repositioned headlights and turbogenerators. These were the engines that lasted deep into the 1950s, most famously on the Elmira Branch serving northern Pennsylvania and central New York. One of the notable photographers who tracked them down was Jim Shaughnessy, and he was impressed when he saw them in helper service: “The ground shook, the exhaust sounds were deafening, and the skies filled with billowing plumes of smoke.” Alas, as research by noted steam author William D. Edson shows, Pennsy scrapped the first Hippo in February 1949 and the dismantling continued apace, thus ending the largest 2-10-0 Decapod fleet. Nevertheless, the railroad kept about 17 of them around until 1960, as protection against an unexpected traffic surge.


Credit PRR for saving one of the Hippos, No. 4483 (Baldwin, 1923). Retired in 1957, the engine was first preserved as part of the Pennsy’s collection of locomotives stored at Northumberland, Pa. Most of those engines ended up at the Railroad Museum of Pennsylvania in Strasburg, but the 4483 took a different route, first acquired by Westinghouse Air Brake as a display at its Pittsburgh headquarters and later sold to the Western New York Railroad Historical Society, which today displays the engine in Hamburg, N.Y.


Two steam locomotives shove on a freight train in a valley
Nos. 3445 and 4268, members of the largest 2-10-0 Decapod fleet, are shoving on the rear of an ore train at Paxinos, Pa. They were shot from the parallel but higher Reading track up the valley on Sept. 14, 1956. Philip R. Hastings photo

One thought on “Largest 2-10-0 Decapod fleet: Pennsy’s I1 ‘Hippos’

  1. it would be great to have a new article on these in the magazene ! especially on the Sodus point branch line !

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