Fort Smith Area Layout

I'm basing my layout in the Fort Smith area. I'd like to have a good selection of MOW stock on the layout. Some of the abrevations I can figure out (B&B + bridges and buildings).
The others however have me baffeled.
Does anyone know the meaning of the following and do the codes following them identify the division they were assigned too?
Gang #3-S.W.
C&S
D.G. 407
C.T.B.
W.S. #7-Cent
S.M.G.

Thanks,

 

C&S = Communications & Signals
DG = District Gang
WS = Water Service
SMG = System Mechanized Gang?

 

Thanks for the info.....Really appreciate it