2 Naval Ideas I always had

[Cyclotron]

Tanks nowadays can be delivered by hovercrafft, amphibious barges, or be amphibious themselves. Perhaps tanks can only be loaded outside of a city with the discovery of amphibious warfare. Mech Inf. are so modern as to be outside these restrictions... just tanks.

[SerapisIV]

In reality there are extensive canal systems stretching thousands of miles across continents - just don't expect anything larger than a barge to travel down it. And definitely not a battleship.

But in the industrial age, all the ships (at least in Civ2) are bigger then barges (definitely by draft at least), so even by letting ships smaller then barges go through canals, you can't build such units. I think that movement bonuses along rivers satisfactorily models barge movement.

[Dauphin]

Serap, it was just a general point and not a game point.

But anyway: Canals in the general sense would really be more of a trade bonus than a movement bonus, and be outdated by the advent of railways. The Silver Cross network in Englnad built at the turn of the 18th century became obsolete within 20 years because of the railways of the 1820s and 1830s.

Only the canals that are shortcuts (Panama, Suez) are still used on a large economic and military level. So by the time you traversed an Eastern European canal system you could have gone the long way round anyway.

As a game issue perhaps there should be a "3 movement points to pass through a canal tile" rule. That would mean that you could build excessively long canals but it wouldn't be worthwhile from a time viewpoint. It could be used to link inland seas to the open seas/ocean.