Yes, you can easily wipe out a small convoy of..let's say 6 ships. The first thing with TMO is to understand how the AI works and attack to your best advantage. Here's a good place to start. You want as many factors in your favor when attacking, because the escorts can easily ruin your set up.
http://www.ducimus.net/sh415/ai.htm
I love the OKane 90 degree attack, but with TMO, your often sensed or picked up and the ships change course and speed so it's hard to attack multiple targets, if any this way..If waters are calm, they will easily see the torps and slow down. If you can do your attack before the escorts come looking, you can use many different methods. I may use OKane for one ship, then use Easy AOB with the stad setting up my other targets.
I use RSRD which reworks convoy layers and convoys can be large, 30-60 ships, but also use this attack with smaller convoys. I stay at a narrow angle go deep and silent coming in between the lead DD and flank. Once the lead DD passes, you have to be careful not to fall into the sonar cone of a flank escort. Course your deep, so you'll have to pass on the ships up from, but that's OK. Come up and shoot the ships towards the rear of the convoy and haul arse, going deep, but flank speed. Your goal is to get out of the zone where the escorts will circle, about 500's from where your torps came from is where they will start hunting. If you can get out of that circle of death where they hunt before they get there, you can keep good speed. The goal is to leave the DD's hunting where you were and why they are hunting, you're setting up your next attack. If you can attack about 1500 from a DD, you should be able to escape the zone they will hunt in. I've done this over and over until all ships are gone.
Another good method at night is to shoot a M14 from long range, say 5000 yards. You do want to try to hit something, but your goal is to pull the DD's away. After you shoot, haul arse and set up an attack from another position closer in why the escorts are looking for you where you once were. Why they're looking, attack again closer in, try not to dive, but if you do, be ready to surface and run.
Main thing is to attack and get away fast before the dd's come looking. You want to alway have the escorts hunting where you were why your attacking from another position. You attack and move, repeat...