ORIGINAL: Mitchellvitch
A point for the AI - and us - to consider regarding the use of German submarines; should they concentrate in wolfpacks in areas of high convoy concentration, or spread out to pick on less defended areas and maximize the number of search rolls?
Yes, that is an interesting consideration (and a similar one is related to strat. bombing - lots of small raids, or few larger ones).
A few thoughts on this:
Wolfpacks:
- if CW/US has no (or very few) available CONV within range to repair damaged lines, then it can really affect CW production to hit a single sea area and remove fx 3-6 CONVs here, or maybe, if very lucky, cut the line entirely (especially later in the war, when the SUB-fleet has been built to a substantial size).
This is also true if the attack is done late in a turn with no time to react for CW
In such cases the goal is not necessarily to destroy the CONVs (although that is of course to be preferred[:)]) - abort is often enough. They just have to be removed from the sea area. (In a few cases it is actually better to not spend surprise points to raise the naval combat column by one, as this will reduce the impact. Fx -X 2D 1A raised to 1X -D -A will mean less damage against the convoy line)
- if lots of enemy SCS/AC are present then damage against the SUBs can be significant
- if CW/US has lots of SCS in reserve, then those will be sent to the sea area after the SUB-pack has arrived, making further searching dangerous
- this tactic is high gain/lose - either the pack finds and does significant damage (especially against weakly-defended lines), or it doesn't find, and no damage is dealt.
- against weakly defended lines with lots of CONVs (10+ to provide increased search bonus) it can be a good tactic. Unfortunately it is rare to encounter such a juicy target

Also, if the German player is not worried about SUB-loses (late in the war, or if he doesn't want to play a BoA) then a pack can deal damage even against well-defended convoy lines (altough the SUBs will suffer as well then)
Spreading out:
- if CW/US concentrates their SCS/AC in a few important sea areas or they are committed to other tasks, or if the Axis get the first impulse, then parts of the convoy lines may be lightly defended (sometimes only by 1-2 SCSs in the 0-box). In that case it is often worthwhile to spread out somwehat
- that will lead to more of a war-of-attrition type of BoA with less randomness
- X results on SUBs tend to be less frequent, as there are less enemy SCS/AC per sea area and less SUBs, meaning usually getting results in the upper left of the naval combat table.
All in all, it is often a matter of preference - I like to spread out, but others may feel differently.
Imho, it depends on a number of factors:
Overall German BoA-strategy:
heavy BoA:
- Build lots of SUBs (be careful about scrapping). Get them out early to maximize # of impulses to make searches, and put pressure on CW.
Would be nice if forcing CW to commit part of its main fleet to other tasks than convoy escort (e.g. German surface fleet or Italian fleet hit CW weak spots)
- try to avoid X results on the SUBs. D can be tolerated, but A is to be preferred, even if it means a little less damage against the CONVs
- use spare HQ(s) to reorg aborted SUBs, and send them back into the fray
- if possible: search every impulse (either Germany, or more often Italy)
- beware of NAVs (incl intercepting NAVs)
- if a sea area is to heavily defended, don't search here
- try to get at least 4 (or better 6) sub-factors in each sea area (and later in the war more), unless convoy lines are very lightly or unprotected in certain sea areas, then even a single half decent SUB can be ok
- coordinate the SUB movement, so SUBs end in as high a box as possible, but preferably not in different boxes in a single sea - that will reduce the effectiveness. Better to keep them together in a slightly lower box and then let the high-speed SUBs move to other sea areas
- if lots of CONVs in only lightly defended sea area, or if CW has committed fleet to overall convoy defense making most or all sea areas to well guarded for to be handled by 1-2 SUBs : send in large pack to try to do significant damage (often best to keep to a max of 4 SUBs per area though, to limit casualties)
no or only light BoA:
- at the occasional spare impulse late in a turn: take combined action and sail entire SUB-pack against important convoy line sea area and go for the find. Use surprise points to increase damage done, rather than decrease damage received
medium BoA:
somewhere in between the above - a matter of personal taste, I guess.
I prefer acting mostly as per 'heavy BoA', though