Tractor Models

- 1st letter = series (size) eg. Z, R, U, G. In themselves the letters had no meaning other than to designate the series - 2nd letter = T (for "tractor")
- 3rd letter = type

The major types:
U = universal (narrow front and adjustable rear tread)
S = standard (fixed wide front and fixed rear tread)
C = cane (fixed wide front hi-clearance)
I = industrial (fixed, heavy duty wide front)
E = extendable (adjustable tread wide front)
N = single front wheel
(There were a few more "type" letter but I cannot recall them offhand...)

Examples: A UTS is a U-series tractor with a standard tread front end. An RTU is a R-series with a narrow front end, etc.
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However in about 1952 when MM came out with the improved "B" series, diesel and butane engines, etc. this model numbering scheme kinda fell apart.

jt

The models you listed are a prime example.

Two of them (WD & NAA) had no reference for anything to the buying public.

The other two (WC & VAC), The "C" stands for row crop version's of the W and VA series tractors in those lines. Allis had the WF which was a standard tread version of the WC. CASE had the VAS (Standard tread)
VAO (Orchard)
VAI (Industrial)
VAIW (Industrial Warehouse tug tractor) VAH (High crop)
The "A" with Case indicates it was the second design of the basic tractor. The VA series isn't such a good example as the V series was really only similiar in outward appearance. Better example with CASE is the L and LA. To further complicate this the C series and D series Case's were very similiar but they changed the first letter, go figure!

To make it even more complicated not everyone used the same designations.

Hope this helps

jt