Why Drive and not Forward?
 

> D- Drive, Well you do "drive " the vehicle but why not F- Forward?

Good question! I honestly don't know the answer, but this page about
the Hydra-Matic suggests narrowing down the search to the immediate
postwar years:
http://members.tripod.com/starchief5...cles.htm#hydra
"...N-H-L-R, in 1946 it was changed to N-Dr-Lo-R. Later it was changed
to P-R-N-D-L to reflect the addition of a "PARK" feature. "

My guess on *why* would be that D-for-drive looks the least like the
other letters.

I've crossposted to rec.autos.antique in search of somebody who has
either researched or personally remembers those early days of
automatics...

Cheers,
--Joe