This writeup refers to European naval tradition, and uses military time.
Prior to the development of reliable mechanical chronometers, the passage of time on naval vessels was tracked by a ship's boy watching a half-hourglass and striking a bell to indicate which half-hour of the day had just passed. The day was divided into six four-hour watches, each of which were divided into eight half-hour segments. When the first half-hour of a watch had passed, the boy would strike the bell once, he would strike it twice once a full hour (two half-hour sements) had passed, and so on until "Eight Bells and All is Well" at the conclusion of the watch.
The watches are called:
It should be noted that Dogs was divided in two (first and second dogs watch), so that those on watch could eat supper.
*aka midnight or 0000
http://www.chinfo.navy.mil/navpalib/questions/bells.html used for factchecking.
This w/u is in the public domain.