Ok you never said whether you're using manual or auto targeting. That makes a big difference.
If you're using auto targeting, then your torpedoes will go anywhere along the ship that you point the crosshairs at. i.e. point at the first mast, and your torpedo will go for the first mast. Aim for under the bridge, it'll hit under the bridge. Forget using the offset dial at all if you're doing it this way. Just point and shoot. Also, make sure your PK is OFF.
If you're using manual targeting, the locked position is basically your "zero position". When you're doing target data gathering, make sure you're locked on to the ship. Once you've gathered all the data, turn on your PK. Now your TDC will follow the "locked" position of the ship (so long as she doesn't change speeds, headings, etc). If you fire using a zero offset, you'll hit the ship where the locked position is (assuming your firing data is accurate). Your offset dial is used to spread your torpedos away from that spot.
Manual targeting example: In the training mission, the locked position on the Mogami travelling left to right is under the second stack (dunno if that's true, but let's just assume so for the sake of explanation.) If your spread dial is set to zero and you fire a torpedo at the ship, it will hit under the second stack. If you change that offset dial, say 1 degree left, your torpedo will travel one degree left off of that "second stack" position. Depending on your range to target, that's going to be somewhere to the aft of the Mogami. The further you are to the target ship, the further behind the second stack the torpedo will hit.
Got it?
