When did baseball caps become part of the Naval Uniform, both
officially and unofficially?

I have seen photos circa 1940 of Army Air Corps line mechanics wearing
something similar. There are newsreels from 1942 showing ADM Halsey
in a ballcap with a rather large bill. I've seen photos and newreels
of other senior officers in similar headgear.

Did they begin in the Air Navy? They are pretty practical working
around recipricators (I guess nothing is appropriate around "hot
tubes" ;-) ).

I've got some historcial "coffee table" books I'll review to see just
how early they show up. I was hoping one of the group may have a
definiative answer!!! :-)