Update Sub unit attack from 4 to 3 (3/1/2)
I'm thinking that subs should start off as 3/2/2 instead of 3/1/2. This way improved subs (+1 attack/defense) could then provide a modest defense in mixed fleets.
This would make improved subs (4/3/2) provide 1 defense (4/1/2) in mixed fleets while advanced subs (6/4/2) provide 2 defense (6/2/2) in mixed fleets.
This also keeps the tradition of incremental increases in power as units are upgraded with the related technologies. Here, that tradition would be extended to the defensive capabilities of subs with 0 defense in mixed fleets < improved subs with 1 defense in mixed fleets < advanced subs with 2 defense in mixed fleets.
Like discussed, advanced subs would be very attractive with +2 attack and +1 defense over improved subs for +2 PU, which would largely relegate improved subs to early losses on attack and sub fodder on defense.