Vanilla bridge battles look too unbalanced for me so I'm thinking of adding swimming capabilities to some units.
What I don't want to do is to review each and every unit so I would prefer to do this automatically based on category, class and mass of the unit.
E.g., light and missile infantry and cavalry look like good candidates to swim unless they are too heavy or their stat_pri_armour is too high.

The extra good point is that in fact can_swim does not require BI

Any comments, ideas or even ready implementations?