Don't have a Tech-talk in front of me, but like Bob states, in '64 or '65 the spray tube porcelain tank dishwasher, gave way to the new "Super-Surge" spray arm & tower arrangement. These machines had the plastisol cushion coated tub and door that were very suceptible to rusting, moreso than the porcelain. Just like GE and others at the time. Eventually, in the very late 70's the inner door panel changed to plastic with formed in detergent dispenser cups. Then of course this machine went away in favor of the WCI dishwasher.