Bulova 1957 Bulova 23 "U"
Unfortunately, I cannot get the back off to check the movement caliber.
I have tried in the past and again today to no avail. It hasn't been in for a service yet, so..........
There are three pin heads (should be four...one is missing), that look like screw heads without the slot, one seated directly next to each lug. I cannot budge them! I imagine the missing one flew across the past owners room and was never seen again. : )
They are somewhat visible between the case and watch strap.