Here is a really unusual one, likely in the "hen's teeth category" Yellow gold plate with stainless back dated 1957. Case back fits against the front of the bezel with a gasket between the caseback and crystal, completely encompassing the movement with split stem and is held in place by 4 pins; one next to each lug. It seems that when the pins are removed, watch is dis-assembled by pushing on the crystal and everything comes out housed in the case back. I haven't attempted to dis-assemble it for fear of doing damage or losing the flat head pins.
This unusual case appears to have only been produced in 1957, but used until 1959 for the Surfmaster, Bulova 23 "U" and in 1959 for the Commodore. The only known examples of this case are all dated 1957 and movement dates from 1957-1959. See my research below.
This example appears to have never been taken apart, and shows no signs of extended wear. Band is a replacement. Running and currently keeping near perfect time.
1957 Surfmaster "B"
Ad is from 1957 Linebook BAWDO131
