Q:

How to organize submarine fleet?

I created a lot of submarines as Germany to try to bring british industry to a halt by cutting off the supply. How to organize submarine fleets for best interception percentage? What are the tradeoffs?
Group size?
For subby hit-and-run smaller fleets (1-3) sounds better but one can hardly afford a leader to all of them, let alone one with a spotter or sub-master skill. Also, I imagine too large a fleet would not be optimal either. 
Distribution?
When to use any such "properly sized" fleets in 1 specific region vs have larger overlapping areas for each sub fleet?
Unfortunately the game seems to lack any strategic "spreadsheet" or diagrams to measure trade interdiction progress.

A:

"Broscience" says the groups of 7-9 subs are most optimal for Germany - good punch and still good stealth.
I am not aware of the possibility to change a supply root tranjectory so it only make sense to set the sub at the busiest regions. If you can handle it one sub group only one region.
Recommended regions: Coast of Africa and mid Atlantic - less British fleet and a lot of traffic, avoid English channel, as too heavily guarded.
General sub tips so far:
- I call sub fleets "sub 1", "sub 2", etc
- Create a many production queues as i have sub fleets and direct the newly produced subs to the fleet directly
- Set engagement level to "not engage" and repair priority to yellow
- Avoid placing subs to the ports easily accessible by enemy bombers (unless you have air superiority) - so basically avoid English channel coast line
- Place a good commander
- Combine subs with nav bombers
Yes, the ledgers are gone, they might be back though. If you keep sub notifications for a month you can see on the map which regions are the most successful and therefore find a good engagement region.

