The War Wagon is a tank-like unit unique to Bohemia, which they can unlock with Hussite Beliefs. War Wagons are heavily armoured and very durable, but slow. They are also incapable of having their attack strength upgraded. They can, however, carry units, just like a ram, and have attack bonuses against unique units (including other war wagons) and archers. The War Wagon can be upgraded to the Hussite War Wagon.
Available to: Bohemia (Requires Hussite Beliefs)
Trained at: Castle
Armor/Pierce Armor: 4/8
Garrison: 2 foot units (not inc. monks, peasants)
Special: +2 vs. unique units and War Cogs, +4 vs. archers; +1 armour vs anti-cavalry, +2 armour vs archers, +1 armour vs unique units and War Cogs
Upgrades to: Hussite War Wagon
Upgrades in: 15th
Range: Siege Engineers
War wagons are kinda weird. They are considered rams/siege units by the game, which means they can have their range upgraded with Siege Engineers and require Localised Interdict to be converted. They still, however, are vulnerable to anticavalry and antiarcher units.
War Wagons can take a huge beating and are almost immune to most units, including skirmishers. But contrary to a widespread opinion, they are not invincible: their attack and range are comparatively small and their lack of speed makes the wagons vulnerable to ranged siege units. They also take extra damage from anticavalry units and antiarcher units (if a unit has bonuses vs both, they stack with each other).
Since their low speed slows down any units they're traveling with, they should be best used defensively rather than in an assault. However, similar to the ram, garrisoned units increase their speed.
During the Hussite Wars, the brilliant Czech commander Jan Zizka developed a battle-winning system of War Wagons. While previously carts and wagons had been used to defend camps, Zizka re-designed the carts to be stronger and be able to contain soldiers to defend them. These carts would form a defensive line, often linked together, with flailmen and spearmen standing between the gaps to protect them. Crossbowmen and handgunners would pepper the enemy from inside the safety of the wagon.