C&O Class J-4 and J-4a
4-8-6 Ohio Type Locomotives
and
Class T-2 2-10-6
Super Texas Type Locomotives

When the C&O ordered the turbines for The Chessie, they also ordered 3 4-8-6 locomotives from Lima as a contingency backup, should the turbines prove not to live up to Baldwin's and Westinghouse's promises. As we now know, the turbines were not a success, but the Ohios were, so the Railway very quickly ordered three more J-4s as well as 4 J-4a's, with streamlined shrouds very like those on the L-1 Hudsons. These engines, the J-4a's in particular, are the ones that made The Chessie the huge success that it eventually became.

In developing the initial specifications for these engines, I'm sure that some C&O motive power officer thought somewhat along these lines:

Start with a J-3a, but it needs a bigger firebox for more power, even bigger than a T-1's firebox, so stick an Allegheny firebox on.  Like the Allegheny, it will need a 6 wheel trailing truck, .  OK, now we need a bigger boiler  to go with that huge firebox, one the size of a T-1 boiler ought to do.  Equip the thing with poppet valves, of course, and put on a bigger tender.  Roller bearings everywhere. 
 
Lets see, what have we got:  a T-1 boiler with an Allegheny firebox, sitting on a 74" drivered 4-8-6 chassis, pulling a T-1 size tender.  Probably weighs about the same as the T-1, but will be taller, because of the higher drivers, about 17' 0".
 
This thing is a beast!  The heaviest thing on 4 driving axles ever, with axle loadings equal to the Allegheny itself, but that's OK, we can handle the Allegheny.
 
Call it Class J-4, but what to name it.  We like to name new locomotives after on-line rivers, but the choices are kinda slim.  "James" type?  Nah!  Sounds stupid, and besides, that river hardly needed this beast.  How about "Ohio" type?  That's better.  Nice big river, just like the engine.

 

Just to show that these engines were actually used, here's a picture of J-4 619 with a fast freight:

As an extension to this design thread, we also tried the same improvements on the T-1 Texas type locomotives, resulting in the T-2 2-10-6 Super Texas heavy freight locomotive:

Further development of the Super Texas lead to the T-3 4-10-6 Lima type:

And ultimately to the class U-1 duplex drive  Lima type

and class U-2 coupled compound duplex drive Lima type