The period from 1938 through the mid-1950s is a particularly interesting period for the American-made lightweights. Schwinn, Westfield, and some of the other American companies in that period earnestly marketed lightweight touring/road-going bikes to adults. They were largely based on British designs and incorporated some of the British parts. Schwinn in particular went big into marketing, showing prominent movie stars on some of the lightweight models as part of the catalog. At some point in the early 1950s, the advertising shifted back to child-oriented, even for the three speeds - kids getting three speed bikes for Christmas and whatnot. The basic wartime utility bikes also fell in that period, though the war was a unique circumstance.
It's interesting that in a period dominated by the American auto industry these companies were pushing bicycling for adults. That period produced some excellent utility and road-going adult bicycles from American manufacturers (I tend to think the Schwinns and Westfields were the best of the bunch, but others turned out some nice bicycles as well), but ultimately I have to believe that only a quite small portion of American adults regularly bicycled for exercise. Thirty years too soon perhaps...