http://www.ebay.com/itm/271234498990
This vintage swimsuit was made in the 1950s or 1960s by Ocean Champion. Ocean Champion was one of the first companies to move away from wool and lastex blends, and into modern materials. This box is slightly later than the other pair I’m listing, rephrased to read “The Choice of World Champions” instead of “Chosen by the U.S. Olympic Team”. The pattern and model is the same.
As the box says, the suit is two independent layers, a trunk within a trunk. At this point, the manufacturer Ocean Pool Supply Co., was headquartered in Huntington Station, Long Island, NY.

Waist (unstretched): 13″ (doubled = 26″)
Waist (stretched): 17″ (doubled = 34″)
Rise: 14-1/2″
Side Seam: 10″