Reference 7923 was the first and only manually-wound Tudor Submariner ever produced. Coming between the other 2 self-winding models the Tudor 7922 and well-known big crown reference 7924. Based on caliber ETA 1156 (21 jewels) it is certainly the rarest of all Tudor Submariners produced in very small quantities probably as a test as the five examples known are all only a few serial numbers apart.