Units with this ability selected cannot attack units with the 'Invisible' ability selected (e.g. Ironclads would not have this ability therefore cannot attack subs --logical, no?).
Pros:
Limits ability of non-ASW units (i.e. not Destroyers, Cruisers, Submarines, Nuclear Submarines) thus making units with this ability (like Destroyers) more useful and unique. Would also give subs a more unique role than just being a missle-carrying invisible unit (i.e. as long as there are not ASW units about, subs can rule the seas thus making them far more strategic unit).
A positive side effect is that you could use this flag for modding purposes (e.g. only snipers can attack invisible snipers?).
Cons:
Human player could exploit this by blocking cities of an enemy civ without the tech necessary to build ASW units ad infinitum thus preventuing that civ from moving ships out.
Pros:
Limits ability of non-ASW units (i.e. not Destroyers, Cruisers, Submarines, Nuclear Submarines) thus making units with this ability (like Destroyers) more useful and unique. Would also give subs a more unique role than just being a missle-carrying invisible unit (i.e. as long as there are not ASW units about, subs can rule the seas thus making them far more strategic unit).
A positive side effect is that you could use this flag for modding purposes (e.g. only snipers can attack invisible snipers?).
Cons:
Human player could exploit this by blocking cities of an enemy civ without the tech necessary to build ASW units ad infinitum thus preventuing that civ from moving ships out.