Aaron Hall apparently went back to the drawing board with the design system in Space Empires IV, because it has its own unique advantages and disadvantages when compared with the design system in SE3. For instance, he removed the idea of "component layers", and replaced it with a special "Armor" ability which can be added to components to cause them to be hit before components without that ability. However, he also added the possibility for components to have variable numbers of hitpoints and varying chances to be hit (though sadly these numbers are inextricably linked). For instance, most components in SE4 have the same number of hitpoints as their size (another change from SE3, where all components had exactly 1 hitpoint), but armor has multiple hitpoints per kT while space yards have fewer hitpoints than kT. Also, mounts were added, which were initially used only to boost the damage of weapons, but quickly found other uses, such as miniaturizing components and scaling them to hull sizes. Oddly enough, SE4 abandoned the Quasi-Newtonian Propulsion model used in earlier SE games, with all mobile SE4 hulls requiring exactly one unit of thrust per unit of movement, but left the possibility for modders to add it back in, which many have done.