I still cant get over the fact that dispite how great SH3 was and SHIV will be, the devs just couldnt manage to script some basic AI patterns for submarines... In a submarine simulator of all things. Im no programmer, but if we strip a submarines desired behavior down to its bare bones, it would be simple case of.
Sub detects enermy ship = sub dives to 15 meters
Sub loses contact with ship = sub surfaces
When ship is within 1.5.km + between 350-10 degrees of bow = shoot torpeedo.
Wow - that piece of rocket science

is not full submarine AI by a long shot, but it would be a vast improvement over what SH3 and 4 currently have in place.... which is of course NOTHING.