In reply to Eric.

Amazing watch, especially considering that you still have the accompanying paperwork! The W10 marking corresponds to the branch to which it was issued (army), so you will also find examples marked with "0552" (navy) in the same place on the case-back.
The approximate 180 examples in circulation are only those that have surfaced. It is virtually a guarantee that the majority of the 1,200 or so examples that were originally issued are no longer in existence today, but the exact number of ref. 5517 watches remaining will almost always remain unconfirmed. There is always the possibility that some individuals out there still have the ones that they were issued back in the day, and that they are simply sitting at the bottom of a drawer or in a box, waiting to be discovered.