I'm experimenting with a new way to create and use armored vehicles. The current method I use is making them from animals and having them function as mounts and war animals, which is all well and good in certain situations but not so good in others. For example, take a modern main battle tank. They are enormously expensive. If we make a human nation, on even the largest setting of DF a given nation could probably max out at around 100,000 citizens. Yet, because DF thinks the tanks are horses, you will find tank fleets numbering in the thousands. A modern nation that small shouldn't have the production capability for something like that, so obviously I need to ensure nations produce a smaller mechanized army overall.
My tenuous solution for this is the transformation of citizens into vehicles via curse or secret interactions. I have created a system in which humans will be transformed into vehicles, made of metal and machinery, but piloted by an organic human brain, representing a human brain extracted and transplanted into a mechanical body. These new cyborg tanks won't be able to equip weapons or armor, but will possess formidable natural weapons along with immense size, making them powerful units in worldgen and gameplay. Furthermore, as they will still be counted as fort citizens, they can be commanded directly, unlike war animals, and special positions can be created to ensure they are appointed military captains in times of war. So, invaders could be living tanks escorted by teams of infantry. Lastly, you will usually not encounter war animals in adventure mode, among bandits for example. However, these transformed war machines can become bandits, meaning that you could encounter enemy vehicles both in fortress and adventure mode. I have yet to solidify a comprehensive system for these mechanics but am optimistic it will succeed.