That's funny, Underway in O C Division, as well as other divisions we stood Port and Starboard duty.
12 on 12 off...
We called it " Turn Your Hat Around and Relieve YOURSELF"
when I crewed on the Niagara we had dog watches. They said it was so each watch could get six hours sleep before the overnight watches. I don't know if that was the original reason for them but it made sense
The original reason was to stagger the watches; since most vessels were set up in two alternate watches, without the "dog watches" the same group of men would always have the same watch schedule.