Thanks for all the responses.. It seems my problem was I was letting him get too close.. even with magnetic it wouldent explode under him. so this time I did things a bit different...
I fired one at the lead Escort, he was crippled. by now they knew where I was, so to hell with Silent running, i put full power and started to close in on the Cruisers. once I had a better angle I launched my rear tube at the escort behind me. it just narrowly hit him on the rear, destroying his rudder, and eventually sinking the ship.. he was down for the count. I fired 3 more torpedos, one at each of the cruisers. 2 were hit on the rear, and one I think the middle.
at this point the 3rd escort was closing in fast. so I started loading my rear tube. he tried DCing me, but I managed to dodge any heavy damage. we cris-crossed about 3 or 4 times before I was ready to strike. and I launched the rear torpedo, hitting right on the bow of the ship. he eventually ran himself into the depths as it quickly flooded.
One of the cruisers was crippled, and limped away at 6 Knots slowly slowing down until its engines flooded. I put another torpedo in her, and she sunk. I caught up to the next ship, making about 8 knots.. I put another in her, and she sunk as well.
the 3rd I couldent find and eventually my game crashed, and my saves seems to be corrupted
So now im going to try and do it all over.
