I also have Line Officers -
I WO Erster Wachoffizier
II WO Zweiter Wachoffizier
These can and will eventually have in order:
1) Watch
2) Gunner
3) Flak/Repair
Engineering -
Leitender Ingenieur
Gets:
1) Machinist
2) Torpedoman
3) Repair
In game terms, Torpedoman is the mechanic who maintains them - most boats had several enlisted/PO under the LI. From the crew listings I get that the Mechaniker ranks were these. The Maschinist ranks were the engine room types - the majority of the crew.
The Obersteuermann and his assistant get the helm - a PO in my boat. As has been mentioned several times, the actual navigator in uboots was this individual - who also was the III WO.
The IV WO was the Oberbootsmann (Bosun) - I generally give him the Repair and station him as the main PO in Damage Control.
This is a bit of overkill - but here is the U 45 as of her loss in late '39: