vehicle designation letters

How are the vehicle codes such as ‘DUKW’ AND ‘CCKW’ derived please?

Am I correct with the following?

1st letter= fuel (D=diesel? C=petrol?)
2nd letter=terrain (U=amphibian? C=land??)
3rd letter=engine position (K=front)
4th letter=driven axle (w=rear wheel drive)

What are other letters for (example) rear mounted engine or 4 wheel drive?

Thanks

D=First year of production code “D” is for 1942
U=Body style “U” utility truck (amphibious)
K=Front wheel drive. GMC still uses that on trucks today (K5 Chevy Blazer)
W=Two rear driving wheels (tandem axle)

B is 1940 and C is 1941 date codes that appear first…

A 1939 Model Year
C Conventional Cab Layout
K Front Axle Driven (selectively)
W Both (Tandem) Rear-axles Driven
X Non-standard (Timkin Supplied) Driveline
353 Chassis Code