I had this exact same problem as the original poster. I read the many tactical comments, tried the "turn and run" tactic and it does draw them near, but the 50 cal/aa fire reduces your speed to nothing eventually and when the torps do come, your a dead duck.
Then, i decided to charge head on at a slight angle so one 3" could be in range, and turned on all weapons ( aa fire ) onto 1 target at a time using the tac map. As soon as the torp alarm went off, switch to 3rd person view, dodge em, and then re-target next ship. Finally, i was down to 2, who had "disappeared" from the map.
Using another tip in this forum, i switched my radar distances and seen a 'red indicator" at edge of map. They do move to a patrol area and after some time i tracked down the last 2 and finished them off. They both hd gone to the North East., even though my last track of them had been to the south west of me.
Hope this helps.
