My favorite tactic as well, though I usually set up between the first and second columns.
Just wait till the real juicy row, usually third or fourth, come by. Shoot the furthest skimmer first and just wait till the others are in the crosshairs.
Then spin around and snap a shot at whatever passed my stern, dive ahead slow moving under the convoy.
Ahead flank after the first explosion for a minute or so, then silent.
Never been located unless I make a fat-fingered mistake.
But then, I'm only in June '42.
