St. John's vision of the fire-breathing horses is about ground warfare. Ancient artists did their best to illustrate what John described, but they didn't see his vision, and the things they are trying to draw are many hundreds of years ahead of them in time, so of course they have absolutely no experience to go by. It wasn't until modern times that we could picture it. The image of battle tanks is from a WWII poster. By the time that Armageddon actually happens, the fire-breathing vehicles will likely be very different from WWII tanks, but it gives us an idea of what will happen.