I think the game randomly sets up a third Kilo. Because i have seen it with 2 and then 3. If the scenario was different where you did not have to protect the tanker, then a slow stealth approach would work using passive sonar. But I doubt that the Kilo's can be picked up using it. Because I was using active sonar I surfaced the boat to avoid grounding it. I went SE of the tanker and went flank while continuously pinging, so I made sure the tanker was a couple of miles away from me, then I slowed to 3 knots. i figured the Kilo's (at least one of them was in water about 140 feet (to the floor). The other was definately surfaced, but those dang harpoons just will not home in one it. So 48's were the only way to go. Interesting that one the submerged Kilo that active sonar would give me a return audible blip, but not strong enough to see the blip on the display, so I had to guess that the boat was in the SE area of the staright somewhat near a land mass jutting out of the water. that may be why the sonar signal was weak. I got the idea of steaming fast and using active sonar from my former COB who was a Torpedoman. They were more up on combat tactics than squids like me who just fixed the boat, but it seems to be the only way to beat this mission.
