100% realism on my S-Boat, 3rd war patrol and 145,000 tons sunk. Thats with a TDC. If there was a switch to remove the TDC I'd use it.
Historically the S-Boat did not hace any such items: Active target ranging, fathometer, or TDC. They did have a Conning tower but I am not sure exactly what it was used for.
Frank