So - this is where I am. However it occurs - point auction, election, funny dances, mime performances, whatever - you end up with the following:
One Skipper - a Lieutenant Commander with zero Notice. A bit older than the other officers (age 34), he is also more skilled, though his physical Attributes have degraded a skosh.
One XO - A senior Lieutenant, he starts with 200 Notice, and at age 30, he is competent enough to take charge in an emergency, though he doesn't rate being the Skipper by rank.
Two other Lieutenants, age 28, with zero Notice. They hope to become XOs eventually, and one day, if they are lucky and skillful, they may attain the holy rank of Skipper. They are competent enough, but they are still young.
Two Lt. jgs (Lieutenant, junior grade), age 26, with zero Notice. They are not mere Ensigns any more, and are vastly proud of this accomplishement. They consider themselves old and wise in the ways of the world. The Lieutenants are amused by them.
Two Ensigns, age 24, with zero Notice. Fresh-faced kids just out of College, Submarine, and Command School, they think they know what to do and are destined for savage disappointment and much skull thumping learning ahead. No one would trust them to mind a watch on their own. They are probably not trusted to find their arse in the dark with both hands.
From this raw material, the Skipper assigns roles, both in battle and out of combat. A Lieutenant, because of his skill set, might be both Navagator out of combat, and Signals Officer in combat. The Skipper might assign himself the role of Approach Officer, manning the periscope or TBT (Target Bearing Transmitter) while his XO is the Assistant Aproach Officer, familiar with the ways of the TDC (Torpedo Data Computer), and able to predict the chase's zig-zag path and plot a course to put the sub in the most favorable attack position. Or he may switch and let the XO or a Lieutenant make those obsevations and keep the big picture in his head using the TDC.
Every Officer has a role to play in combat. The Approach Officer may shout "Fire One!", but the result is a team effort.