The interesting thing is why PRR did not evolve fast 2-8-4s after the Erie and the Van Sweringen AMC developed the first ones at the end of the Twenties.
Remember that the M1 4-8-2 was cutting-edge modern just a couple of years before Woodard's A1. PRR liked the four-wheel lead truck on its high-speed power right up through the Q1 and Q2 (which PRR considered to be 5/4 of a M-class engine as the logical evolution).
The AMC design for the C&O T1 (the various AMC Berks were scaled down from this, not the other way around) was essentially forced on PRR for production power (hence among other things the absence of a Belpaire firebox even in the postwar years when whole classes like the NYC Niagaras and ATSF 3460s needed their boilers replaced en masse. What made the J1 so uniquely good on PRR over the Q2 was that the latter was actually a high-speed locomotive -- that was highly useful during wartime, moving 150-car freights at passenger-train speed, but in the postwar world of 50moh freight restriction there was no need for the complexity, handling quirks, and maintenance cost of the duplexes vs. a 2-10-4 with acceptable augment even with spoked mains at that speed.
Needless to say, had PRR wanted a 4-8-4 (which would probably have started with R2) there were several broad possibilities. One might have been the locomotive pictured on deviantart as a T1 with the center cylinders lopped out... but any PRR 4-8-4 would have had at least the 102-104' GA in Baldwin's original proposal. (Driver diameter is an open alternative-history question; I suspect 72" with modern balancing, but it might have been the 77" of the Q1, or the 76" that would have been mandated by a double-Belpaire chamber).
The more likely R locomotive wouldn't have been reciprocating at all; it would have been a geared direct-drive turbine along the lines of what Westinghouse was peddling as late as 1948, with the 2-speed planetary that fixed most of the starting issues and eliminated the wrongheaded gear-reduction reverse turbine. Look for the use of a J1-scale boiler (the drivers being no higher than the S2's 68") which would likely been one of, if not the greatest of, 4-8-4 locomotives. But this came literally about a year too late to matter to anybody...
Ok, Duplexi they are
Both V locomotive designs were turbines, with the former being mechanical and the later version having the Bowes drive. You're thinking of the B&O W-1 'constant torque'.
There were some veeeeery strange designs toward the end of the 1930s, including the stillborn Steamotive designs. I don't know if those were given working class numbers; there would probably be information in some of the Hagley material in Delaware but you'd probably have to go through the boxes to find it.
And DON'T call them 'duplexii', it's like a double sharp stick in the eye, once for the locomotives and another for the wack Latin. Reed was being playful, but he's had his fun and we can go back to common sense. They are 'duplexes'.
The class U I remember was an 0-4-0, a short-wheelbase shop switcher which I remember as having both bunkers and saddle tank to keep the length as well as the wheelbase down. I believe these were rebuilt into the A3s but I don't know what, if anything, changed.
The original class T was something very, very different from just about anything else, on the PRR or elsewhere! There is actually a picture of it at speed with a considerable train, I think on the then-relatively-new high speed line through New Jersey, which is proof of a sort that with care the arrangement could be made to balance well.
OK, we all know the PRR's Class T was its 4-4-4-4 Duplexii and Class V steam motor locomotice was a 4-2-2-2-2-4 with a V4 steam motor on each driving axle. Which leaves the question of what was Class U? I know one site has an imaginary history that says it was a 2-8-4, but that's obviously fictional. So I call on your collective knowlege of the arcnane, what was it?
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