[Hitman]

RE the always complicated AI subs, wonder if this other way of making them work would be of some use?

Based on the usual peri depth "destroyer" unit, attach a series of surfaced submarines to it at different depths, that become visible only at certain distances. So as you approach you will see it "sink", and as you open the distance it will "surface".

This could work for AI hunter killers, so that if you are able to spot them in time you can evade or go chasing them.