The M-84 tank is currently in active use by the Armed Forces of the Republic of Croatia. Considering the fact that the tank was designed in the 1970s, it is necessary to assess the level of its armor protection against the more modern threats frequently encountered today. This thesis deals with the assessment of the armor protection of the upper glacis of the M-84 tank against the Soviet-made APFSDS (Armor-Piercing Fin-Stabilized Discarding Sabot) subcaliber projectiles, which are still in use today. The penetration capability of the projectiles is calculated using an analytical expression known as the Lanz-Odermatt equation. This equation is programmed in the Python programming language. Parameters defined by the equation, related to the projectile and the target, are defined as input. The obtained results are compared with the effective thickness of the armor configuration of the upper glacis. Finally, a potential improvement of the level of the tank's armor protection is proposed by adding a layer of ceramic. Ceramic is a material of high hardness that erodes and fragments the projectile, thereby reducing its penetration capability and increasing the vehicle's armor protection.