Surely, the odds will be in your favor later, and you'll get some straight-runners... I've been hit by 3 of them over the years. I "recorded" the last incident. I do have to get that clip into my movie maker thingie and post it... It is quite entertaining. This last one hit in the forward torpedo room area, and when I saw it going in a circle, I hit All Ahead Flank to try to get out of its way, and instead, ran right into it. I sat still the time before, and it hit the shears... Once, it hit the very middle of the boat, but was a dud...
... It'd be really cool if they could have "modeled" that, and you'd go back into port with a torpedo hanging out the side... 'Course, I would think the would attempt to get it out, plug the hole, remove the charge, and take the miscreant back with them for further investigation...
Now, if you're talking about a torpedo coming out of the tube, running a couple hundred yards straight, then turning toward the target and then running true after that, that's the way they are designed to go. It's the gyro off-set. If they're circle-runners, they turn and just keep turning. Sometimes, they turn as soon as they come out of the tube...