In keeping with a few others that have popped up around my shop recently, I find myself with this oddity. This one is unusually thin, the height of the entire assembled watch is only 7.2 mm including the crystal. I would estimate the thickness of the case without crystal at 5.5 mm. The outer bezel is concave, which I don't think I have seen before on a Bulova.
US patent 2871654 refers to a waterproof case design by Emil Fachon, working for Bulova at the time. Filed April 14, 1954 and published Feb 3, 1959.
It follows the design of the Watertites in that the case back is deep and pressure fits to the bezel and uses an armée crystal as well as pressure form the bezel to seal the case. The case is 34 mm which is a decent size for the period, and I think it will polish up well and be a good candidate for full restoration.