This is Ref. F4786, a glorious British military watch. The case size is 37.5 mm, which is quite comfortable to wear. The stainless steel contributed to such a long life and the fact that this watch fulfilled its purpose. It is enhanced by a Nato leather strap, which gives it the complete vintage look.
It comes with its original dial and hands, but the case number does not match the case back. One of the reasons why this happens when the numbers do not match is that several of these watches were sent in lots for maintenance and the case backs were randomly placed on each watch.