lazy guy I have not read the above post that well...
well... here goes:
my tactic is as follows.
I try to slip in between the front and on of the flank escorts at peridepth and silent running or let them steam by fully stopped (this is tricky I know but works well)
till now this has always worked (march '42)except for a few cases and then it was my fault not going fll stop soon enough and they heard me and started a pin-search
while that moment I am between the escorts I estimate the speed of the convoy in general (OLC GUI) and pick my targets looking out for the big ones...
I always try to get at least one of the big fish and pick others to unload all my torps then I dive and see that I get myself out of there or if luck is a lady and the escorts start to go woozy-loozy (not knowing where I am and start freaking out)
then I reload and pick me other targets.
to avoid depth charges dropped on my boat (the DDs can't be stupid forever and will soon enough figure out where I am) I usually go very close to one merchent using it as cover as the DDs and DEs then can't get in range for the depth charges - it's a dance with the devil but also is fun
If you ever get into the situation a DD is heading straight for you (position I mean) - having found you! - in shallow water... don't dive - don't panic!
Go all ahead flank and wait till he is at around 300-500m and then make a very sharp turn away (meaning if you were heading to the left go all rudder fully left) and watch him pass you in your back and just when he is passing your back go all right (the other direction). In 80% of all cases I was not hit... the other 20 get tricky... I have seen everything from light damage to fully destroyed compartment and hull to 50% by one charge once - very bad luck (hit my boat right on the deck - the DDs shoot some off their sides)
This is when you are already moving away from the DD
If you are moving towards it... you have to make the turn sooner but in general the same idea.
Try to get into the "safe" zone between his back and the point he shoots his sideward charges.
Others will say crashdive... I say play cat and mouse once and then crash dive (well not in shallow water) or shoot him after he passed you cause ...
When the DD has passed you he will make a turn for a second attempt and usually slows down to ~10kts at around 400m ... and shows his full broadside - easy target!
If the escort is just searching you can also try to get away from the spot he thinks he saw you at silent running and at 600m stop the enginees - hoping he will not ping you... if he pings... He will find you!
If he does not the chance you get away is great! He will drop his load where he thinks you were while you can sneak away.
or you shoot him if he really heads straight at you set the torp to magnetic and 0-5-1m under his keel. - But good kaleuns don't waste torps on little DDs, no?
If there is more than one of the and time is not enough to shoot one or you just don't want to waste y torp... get out crashdiving the moment you make your "counterturn" - go to depth quick;
I go to 100m set silent running on and make a 90°turn lft or right away from the convoy... then the dance starts. I try to go to 160m till 42 this is a save depth imho for not being detected too easily.
I also attack at night when possible
Keep your periscope as close to the watersurface as possible to avoid detection...
anything else... dunno... just try around... there are many ways