What I do depends on the year. I am currently in 1944Q2 so I follow something like this routine:

1. Follow the escort out of harbour at TCx8 until he turns around.
2. Set speed ahead flank.
3. Plot a course to my assigned patrol area and back to base as follows. If leaving a French base, go through the southern half of the Bay of Biscay. Once out of Biscay, or Fjords, set course as follows. If patrol area is in the air gap, plot shortest course to edge of air coverage, then shortest course outside of air coverage to patrol area. If patrol area is inside air coverage, plot shortest route to patrol area.
4. Once I have 20m water under keel, dive to periscope depth.
5. If time is between 23:00 and 03:00 or between 08:00 and 16:00, set speed to 2.9 knots, else 1.9 knots.
6. Set TCx32.
7. At 19:00, set TCx1024 (TCx128 if within 75km of base)
8. Once I again have 20m water under keel, dive to 25m.
9. If time is between 16:00 and 03:00, run submerged until 07:00 else until 16:00.
10. Set TCx32
11. Go to periscope depth.
12. Check weather.
13. If fog is medium or heavy, or we are ouside air coverage, set speed ahead 1/3 else if wind speed > 9m/s set speed ahead full, else set speed ahead flank.
14. Surface.
15. If wind speed < 6m/s run decks awash, else, if wind speed <= 9m/s. run decks partly awash.
16. Recharge batteries.
17. If fog medium or heavy or outside air coverage, set TCx1024 until fog light or none or inside air coverage, then TCx32.
18. If fog light or none and batteries fully recharged and in air coverage, submerge to 25m.
19. Repeat from step 5.
20. If aircraft detected far off, crash dive.
21. If aircraft detected too close, man flak guns, fight off aircraft, crash dive after it drops its bombs.
22. If battery charged < 90% set speed 0.9 knots else set speed 1.9 knots.
23. Stay submerged for at least 24 hours.
24. Repeat from step 11.
25. If a radio contact is received and is within range, plot intercept and attack.
26. Goto step 30.
27. If we detect a contact on our own, observe its course and speed, then intercept.
28. if contact is a convoy or task force, report contact.
29. Attack.
30. Repeat intercept and attack until enemy destroyed, or out of ammo, or too damaged to continue.
31. When arrive at patrol area, patrol for 24 hours as follows: Run about 100km on a course perpendicular to expected traffic, run a few km parallel to expected traffic, run 100km on reciprocal of first patrol course. Complete the loop. Repeat.
32. If fog medium or heavy or patrolling in air gap, submerge every 2 hours for sound check, else run submerged except to recharge as in steps 5 - 19 above.
33. After 24 hours, randomly decide whether to move to an adacent grid square.
34. Repeat from step 32.
35. Once torpedoes expended or too much damage, return home by reverse course.
36. Same submerged/recharging routine until depth below keel < 10m, then surface and run at flank at TCx32 until 5km from base, then reduce speed to 1/3, TC to 8.
37. Inside harbour reduce to slow.
38. Reverse into berth.
39. Accept flowers from prettiest nurse, suggest she come to my quarters to help arrange them, right after I have filed my report.

Notes on certain steps:
3. There is less air coverage is the southern part of the Bay of Biscay, and fewer surface patrols as you exit the Bay from the south.
5. I set these speeds so it won't take too long to recharge batteries at 07:00 and 16:00.
7. I run 12 hours at TCx1024 so fatigue state and watch changes line up (4 and 6 hour watches run a complete cycle every 12 hours), and to minimize contacts detected while submereged because there are too many ships in the game.
13. Where aircraft cannot can't operate e want to conserve fuel, else we want to be going at least 10 knots, to reduce dive times.
15. If weather allows, I run decks awash so as to reduce dive times and to be harder to detect.
16. It should usually take no more than 80 minutres to fully recharge.
18 . I run surfaced at TC32 when aircraft might spot me.
33. Kaleuns didn't decide where to patrol. BdU did.

Good stuff there Roald :up:

I am actually looking forward to 1944,as surely the game will be far more complex and hazardous by then :o

In general, my approach is:
- Leave port
- Plot course to assigned patrol grid, via high traffic routes/areas.
- Stay primarily surfaced on the way, but submerge and listen at least once in a 24 hour period. (I figure BDU wants me at the assigned grid, so I don't delay too much on the outward journey).
- When I reach my patrol grid, I patrol for at least 24hrs, per my orders. I set my own pattern, based on the grid, expected traffic patterns, allied air cover, weather, etc.
- After fulfilling my orders, I head to what I feel will be the best hunting, while considering the safety of my boat (e.g. I don't do harbor raids). I stay out until my eels are near spent or my fuel begins to run low.
- I have learned to keel one torpedo for the trip home, since I always seem to find a nice target on the return trip when I don't have any! If nothing shows up, I'll find something to sink just prior to heading into home waters (I hate bringin a torpedo home!).