This vintage swimsuit was made by Jantzen and was sold in Brooklyn, New York by the Schwartz Mens Shop. It is the “Half Hitch” model, produced from 1936-1942, recognizable by its tunneled buttonhole belt loop arrangement, narrow belt with hammered look buckle and side piping.
These vintage swim trunks were made by Jantzen in the late 1930s. This particular model was known as the “half-hitch”, after its half-concealed belt. That model was made from about 1937-1942. This is one of the earlier versions of it. Unfortunately, they are heavily moth eaten.