I have wanted one of these for my RAF collection since they came out, but was waiting patiently for a bargain, grabbed this one in the NN sale, the watch looks as new to me.
There is no serial number on the watch, although the paperwork and user manual have 00/1940, so this must be a pre-production model which is fine by me. The case back is also engraved with 25 jewels so probably contains an ETA 2824, the water resistance is also engraved as 10ATM, checking the CW site pictures the main pic of the case back has 5ATM and 26 jewels although there is a second pic that shows the back of the watch that is the same as mine (except mine has no serial number). Maybe fitting a Sellita movement reduces the water resistance by 5ATM. All the other C5 models are engraved 5ATM so this must be the actual WR.
The watch came on the plain black strap which does not look right to me, so grabbed a 22mm tan strap from my spares box and notched it down to fit as a temporary fix, will be looking for a new strap for this one, Mr Rick has a couple of nice one's for his C5 B of B.
The watch is running +20 secs after 24 hours, once it has settled in will probably regulate it and check the movement at the same time.
So some pics.

Looks good on that tan strap - well done!

That looks superb ~ well done from me too

Nice catch, especially in the sale.

Very nice look. When I first saw the photo of the strap on the watch I said..oops..a bit big...then I see the wrist shot and it looks real good. Well done!

I suspect you have a developement prototype there, which would explain the lack of serial number as well as the 10atm marking. The movement would not affect the atm rating as this case was designed for a 5 atm rating since its inception.

A nice piece to hang on to.

I do think the BoB is the best looking C5, well done on the purchase

Very nice indeed - great pick-up!