Erie's Triplex locomotives - machines so big they inspire, intrigue, and move the mind as much as they could move freight. Built in an era when the compound Mallet design was just coming onto the scene, the Triplex took the concept a step further in attempt to use not only the locomotive's weight but also that of the tender for traction. On paper at least, the locomotives could put 89% of their loaded weight to use and pull a train 5 miles long. They were so powerful that you couldn't put enough weight behind them to truly test it without breaking couplers and by some accounts remain the most powerful locomotives ever built. The first Triplex entered service in 1914 as number 2603 and named after a prominent and recently retired engineer on the Erie, Matt H. Shay. The locomotive was as much of a marketing statement for the Erie as it was motive power. The locomotive performed well enough that two more were delivered in 1916 with only a few minor modifications from the original. The three were assigned as helper engines on the Susquehanna Division - best known as the line over Starrucca Viaduct. The Triplex was a compound Mallet, with high pressure steam going to the center pair of pistons first. The left piston exhausted steam to the front pair of pistons and the right to the rear which powered the wheels under the tender. The locomotives were also unique in that both the high- and low-pressure pistons were the same size, using different valve sizes to accommodate the changes in pressure. Predictably, the problem with these large beasts was not power, but appetite. The boiler would struggle to keep up pressure against the consumption of six cylinders - even if it was only directly feeding two. And although there were elements in the design to compensate for variable traction under the tender as fuel was consumed, as it ran light wheel slipping could be an issue. The locomotives stayed in service until as late as 1933. Only the Virginian made another attempt at a Triplex with a single locomotive. It was rebuilt as a smaller 2-8-8-2 soon after, however. While not a major success, they were certainly not a failure as far as experimental steam designs are concerned. More accurately, they were truly too big for their time. It would have been interesting to see the concept revisited a few decades later when technology had improved and train weights increased, but alas it never came to be. To bring this locomotive back to the O Scale market as anything less than a VISION LINE model would be a crime! We have packed every inch of this massive machine with amazing features including the all-new wheel slip simulation. If your labor rate gets too high or the fuel is running low, watch out! Those rear wheels might just start to slip. Not just a sound effect this time, the tender drive wheels have independent motor control and will actually slip under the right conditions. And when the wheels slip, of course the sounds and smoke will follow along. Other notable features include whistle steam effects, a swinging bell, road-number specific crew talk and 4-digit addressing. We've also made several tooling changes to model both the "production" models of 5015 and 5016 and the prototype Matt H. Shay. Few locomotives will make a bigger impression than the Triplex.