Because iron in the game represents surface veins that can be scratch-mined, or meteoric iron. By the time you've got bombers it's assumed you've got the tech to do deep shaft mining, meaning that iron is plentiful and you can find it everywhere. The reason it's needed still for rails and factories, imo, is that you need *alot* of iron for these things, so iron then represents the really massive deposits.
Infantry units are the WW1/WW2 kind, whereas riflemen covers the period from the invention of the rifled barrel up to the early 1900s or so. By the time you'd have kevlar you'd be using APCs and those are mech inf.
The reason rubber is needed for infantry (which are supposed to be WW2 era infantry, mainly) is primarily because it was needed for the tires of army vehicles (for supply, transportation, etc) but also because plastics technology was not as advanced and they couldn't spare the oil, so rubber was commonly used in its place (especially for flexible plastics, which were not very good at the time). Also leather was in short supply. So alot of bits of gear in a soldiers' kit or basic equipment for camps etc - especially anything that had to be air or waterproof (gaskets, hoses, gasmasks, hundreds of different little things) or flexible and strong - was made of real rubber. Rubber's importance in WW2 cannot be stressed enough, there are hundreds of propaganda posters from the time about rubber. Here's one:
However, it doesn't make sense to require rubber after the WW2 age, the end of the third era, because it's mostly synthetic substitutes now, so imo none of the modern units should require it.
L = 50.
Very cool
