I think I have found it.

1945-194?- white metal. This is not a good descriptive.
1949- Nickel-chrome case by Keystone.
1950- Non-magnetic stainless steel, made by Star Watch Co.; The No. 15 case used by Hamilton as an economy model, priced at $71.50.
Used until production ceased.

See- http://www.watchdoctor.biz/pocket.php.

Data from catalogues sent to Hamilton wholesalers, thus fairly reliable.

A lot of information can be found by putting various entries in google.
Took me 2 hours to get to this data. I will post my bill for this service after I figure all the add-ons.