Abstract: A system of armor plates is adapted for protection of a structure against projectiles B and S of two characteristic calibers DB and DS, DB>DS. The system compres a main armor plate and an auxiliary plate mounted in front of the main armor plate at a distance therefrom. The auxiliary plate comprises a plate made of ballistic material and perforated with through holes of characteristic diameter D, 1.2 DB>D>1.2 DS. At least one hard-material body of diameter DH is disposed in each of the holes, such that the auxiliary plate provides at least destabilization of impacting projectiles S capable of free passage through an unobstructed hole of diameter D.