I have gotten a request for some pictures of what was under the M-1's shroud. Here are a few pics, scanned from the book "C&O Power"
The boiler of the M-1 taking shape at Baldwin's erection shop. It was
basically the same as a conventional steam loco boiler except the orientation
- the firebox was closest to the front end of the loco.
A close-up of the piping showing how complex this engine was. The rectangular box in the middle is the feedwater heater. Compare that mess to the side of a typical steam engine!
Another shot of the tangle of pipes and wires that was the M-1. Those
pipes on the top right delivered steam to the turbine.