A armor system for protecting a vehicle from a projectile, the projectile having an expected trajectory and the vehicle having a hull, is disclosed. The armor system has a modular armor subsystem configured to be mounted exterior to the vehicle hull. The modular armor subsystem has a leading layer having metal, leading relative to the expected projectile trajectory, and an intermediate sheet-like layer having low density material, of a density less than metal, abutting a rear surface of the leading layer. The armor system also has an intermediate sheet-like layer having glass fiber material and abutting a rear surface of the intermediate low density material layer, and an intermediate sheet-like layer having metal and abutting a rear surface of the intermediate glass fiber layer.