I'm a bit puzzled by this.
I always thought the PWO is in charge of the ops room, just as the OOW is in charge of the bridge.
So, if there are only two PWO's on board, does that mean PWO's have to work one watch on, one watch off (as in defence stations six-on-six-off)?
Surely, working three watch cruising stations would mean that every ship needs a minimum of three PWO's?
When in cruising watches the PWOs don't keep watches, they will close up in the Ops Room for certain evolutions. Some may even keep the occasional watch on the bridge to keep their hand in and give the young'uns a night off!