Well if you are talking about ... say... a M-35 Duece, the M means military.
If it is Air Force, as in 95B3456,
95 is the year
B is the management code
and 3456 is the numerical order of puchase, meaning it was the 3,456th vehicle purchased in 1995.
management codes:
B - general pupose vehicles and equipment
C-specialty trucks
D-construction equipment
E-material handling
K- military vehicles
L- Fire fighting, refueling
W-miscellaneous
X- unit purchased and maintained vehicles
Wroper