This is an interesting case. The watch is nothing special. But the back. It is the old Zenith signature. So that the signature is always the correct position, the caseback that has a nose that is attached with a ring. The calibre is 106-50-6. I found still no second watch in this form.
That is interesting - I have never seen one like this before, either. Is there anything on the inside of the case back?
I 've seen these in the past, and I don't know for certain how to explain them. I do note the unexpectedly low movement number - off by an order of magnitude from the more usual ones - and the caseback number that typically does not fit in the usual sequences. This leads me to believe this caseback may have come on watches from the Besancon factory. Note the absence of "Swiss" on the dial, the caseback or anywhere else.
Thanks for the comment. I think that the watch was born about 1938 and I'm not sure whether this time "Swiss" or "Swiss Made" already has been printed. But Besancon is a possibility.
I've seen that shield associated with vintage Zenith but never on a case back. Not that I have huge experience in vintage Z so take that with a grain of salt but it's a Zenith logo