A few days ago I started a long post about my ideas, with pros&cons, detailed reasons, etc. However, I lost it so here is my shorter list. If needed I can try to write about the details again Ironworks could grant a few (2-4) iron and maybe Factory also could grant 1. Why? I run into some map where iron was very-very rare and most of the major civs was unable to build ranged naval unit or siege unit starting from the industrial Coal and Aluminium has their own building that grant a few resource I am not afraid that it would cause balance issue, because if you already have 10-15 iron these additional few wouldn't be a big impact. However if you have 0, these few could be very-very useful. In case the above is not welcomed, please consider to extend the time while Frigate is available. After industrial (without iron) you are in an unbalanced situation on the sea. While you can live without "iron based" siege units because you can use resource less ranged units instead. However, you cannot do the same with naval units. You can only build melee naval units.... Make the hydroplant/windmill user selectable like trainstation/seaport in case the terrain conditions are met. So be able to build windmill in a riverside city if that would be a better option. One tile river is the most know reason why should these building user selectable while well/watermill roughly provide the same amount of extra yield so they are more balanced. I would even consider to make hydroplant available for non-riverside cities if let say river can be found in 2 range Nuclear weapons could degrade the great person progress like the sabotage. It is not a balance issue, I just find it weird that while 50-70% of your city pop is dead your great person progress is intact. Thanks for any feedback.