Help with Officer Designations

[Piggy]

Can anyone explain the specific officer designations (think that's what its called).

The following are obvious ( I think)

Watch Officer = Captain
Boatswain = Second in command?
Engineer/Mechanic/radio etc.

Question is what do the following roles entail and are they necessary/what bonus? (IE: in the case of medic, I've had other officers that fill that role when needed so why a special designation)?

Technical Officer?
Quartermaster?
Medic?

Also, and this may have been fixed in the recent patch but when I gave officers new skills they were suddenly not able to perform all the tasks they previously did?

[Glas]

Hello Canada
Tech officer Hydrophones, Quartermaster supplies guns and medic heals without a med kit. I always leave one officer unassigned for first person view and to assign as I see fit. Left down screen corner gives explanation just click on the tasks.
Good luck from Holland.