Infact we can add 2 cards
1.This card is an age 4 card,to all European nations and Mexico,this card will allow artillery foundry and fort build normal gatling gun,just like those 2 pictures.
2.This card is also an age 4 card,to all European nations,USA and Mexico,this card will upgrade gatling gun to the Heavy Gatling Guns,and removes gatling guns packing animation.
I think this will make the game more interesting,and reflecting technological progress.