heh, i just wait till its around 10 oclock at night till about 3, and then i rush in, ALL AHEAD FLANK! fire all my torps and go under the convoy, then after loading torps, ill come up periscope depth and launch all bow and aft torps at all available targets, and then fire the deckgun

and personally man my 37mm AA gun. till the destroyers and escorts close in and start firing at me... with luck they hit the surrounding convoy, then ill dive deep under the convoy after sinking about 5-10 ships ( always target the biggest ship first, thats yer prize!) then execute your best escape and evade manuvres.
sometimes to throw sh!t into the wind ill take on one of the escorts...
some of you may call me crazy... i just say ive got balls... and hell Hindrich Willembrock did the same!
plus what destroyer is gunna expect a crazed lone wolf attacking his ducklings headon like that? if you manage to take out the destroyer escorts ( good luck with that however... ive done that ONCE! and ive failed countless times:rotfl: )
the convoy is like lambs to the slaughter... especially if you get inbetween them!
as golden rivit says... shadow em... thats the key... establish a pattern, and report the contact in... aparently if you do that a bunch of times and shadow the convoy a few days ( its worth it trust me... id rather take out 10 ships in a few days and take decent-severe damage from one convoy then endlessly search for 5 ships.) subs will show up on your contact update, and eventually show up at the convoy, giving the 3-4 escorts a reaaal hard time
4-5 uboats vs 3 destroyers? not enough depthcharges to go around!