Of course, it was possible to put a round movement in a square case and there are plenty of square models to choose from. There aren't that many with a sweep second hand though. One of them is the 1959 Sea-Mate.
The Sea-Mate was produced through 1961 and came on a strap or a bracelet. The bracelet is shown in the catalog image - although I'm not really sure what it truly looks like.
Inside the 10K rolled gold plated case with stainless steel back is a Swiss-made Hamilton 671 movement made by ETA. The case on the Sea-Mate is oddly constructed in order to be "waterproof". Although the back snaps onto the front, the movement still uses a two-piece stem - almost like the set up you see on the CLD models from earlier in the 1950's.
You don't tend to see Sea-Mates very often. I don't know if I'd say the model was rare - after all, it was one of the least expensive models of the era. Maybe it wasn't very popular?
I recently purchased a Sea-Mate mainly because I'd never seen one before. It wasn't in particularly good shape and the hands were obvious replacements as they are the wrong style and they are a little too small as well.
The crystal in the Sea Mate is very odd. There is no ledge in the bezel for a conventional crystal. Instead, the crystal has a ledge around all four sides so it passes through the bezel from behind and rests, presumably, on the dial. I suspect there should be a gasket involved somewhere, this is a "water proof" watch after all, but there wasn't one inside this watch.
The crystal has a small crack in it and a few scratches that won't polish out. So I'll need to purchase a replacement. Fortunately, a quick perusal through the GS catalog reveals the Sea-Mate takes a CMS 980.
The dial and movement fit securely in the stainless steel back. So I need to located the gap in the female side of the stem so I can swing the movement out. You can see in the shot below that the embossed dial has a circular texture pattern along with the markers and pearled track. This would be a tricky dial to get redone correctly, I bet.
The 671 movement is very similar to the ETA automatics from the same period, just without the automatic parts. It fact, it shares a lot of parts with the ETA 679, etc.
Everything is cleaned and dried before being reassembled.
The running movement has good motion so it's off to the timer to see for sure how it's performing.
A little fast but that's pretty much where I like to see them when they're reassembled. I'll check it again after it runs for a while.
I happened to have the proper hands for the Sea-Mate so I installed them along with a better Hamilton waterproof crown. The watch will look a little better once I put a new crystal on it but it's not too bad as is.