This thread may be helpful to you....
http://www.subsim.com/phpBB/viewtopi...=435470#435470
Basically, if firing a mk48, a range of around 12nm is usually good for a surface target, 10nm for a typical 30+ knot SSN. Those ranges will ensure that your torps will not be outrun... the targets can, however, still evade the torps laterally at most ranges, so torp wire guidance is a huge boost.