Vintage 1950's swimwear owes it's molded, corset style to great innovations in textiles suitable for beach and pool. One brand, Beaunit Fabric, produced fashionable satins that could stretch by using elastic fibers.
This industry ad from a spring 1951 issue of "California Stylist" also promotes the "Surf Tog" label, showing a princess seam line strapless swimsuit that would have had a zipper down the center back. It has dress maker details including a cuffed sweet heart neckline with bow and a modest sheath skirt to cover the upper leg.