LV diesel classification?

A recently posted photo of U23B 508 on the "Fallen Flags" site
http://www.rr-fallenflags.org/lv/lv0508o02.jpg" onclick="window.open(this.href);return false;
shows the railroad's class on the cab side: GFM-22. "GF" would, I assume, mean General Electric - Freight, and the 22 would be the horsepower in hundreds rounded down to the nearest hundred: compare the Alco C628's Lehigh Valley class AF-27. But what is the "M" for?

Maybe it is for MU capability. The other thought is the M is for a modification to a similar model. The C628 had the original, and ex Monon. There might have been slight differences between the two. Some railroads kept the same class for 1000 hp switchers. When EMD switched from NW2, SW7, SW9, SW 1200, they were essentially the same. There was a thread about how they re passed the GP9, and GP18, since they were so similar.

1160-B CLASS OF ENGINES - DESIGNATION CODE

LETTERS

• A- ALCO
  E - EMD
  G - GE
  S - Switcher
  RS - Road Switcher
  F- Road Freight
  M - Multiple

- LV timetable #10, effective August 10 1975, page 135. List is followed by explanation of the horsepower numbers.

Lvrr325--
Thanks for answering an old question!
"M" probably made more sense in the first generation of dieselization: many railroads bought switchers (and I suppose some road switchers) without multi-unit capability, and whether or not a unit could be hooked up with others is certainly a piece of information the operating department would want to have available. I believe the LV's corporate "cousin," the PRR, also had an "m" suffix on the class designation for multiple-unit equipped switchers.

Continuing to use the suffix in the 1970s... would have been a matter of tradition. Were any U23B built WITHOUT m.u. capability? (Not impossible, for a few were built for dedicated mine service (in Peru and Texas) where the operators may not have seen any likelihood of m.u. operation.)