Reactive Armor is a type of vehicle armor addition that reacts to the impact of anti-vehicle weapons by way of exploding. The explosion disrupts and deflects the projectile, preventing catastrophic damage to the rest of the vehicle.
In Battlefield 3, the term is also used for slat armor, which defeats anti-vehicle weapons by causing them to detonate prematurely, well away from the actual skin of the vehicle. The vehicle's primary armor can withstand the diffused impact much better than it could a direct hit.
Battlefield: Bad Company 2
— Battlelog description
In the mission, Thunder Run, the M1 Abrams of Jonathan Miller and Ingham are equipped with the Reactive Armor. This reduces the damage done as the tank can last up to 5-8 shots of enemy sabot without being destroyed. However, this is only available on the said mission, as the tank is more vulnerable to tank sabot in the mission "Fear No Evil".
Reactive Armor is a specialization for tanks and other ground vehicles. On the driver's HUD, linear icons appear flush against the vehicle body icon, representing additional protection against certain sides of the vehicle. Like other specializations, it is only active if the driver has selected this gadget.
Main Battle Tanks receive side and rear reactive armor. IFVs, Tank Destroyers and mobile anti-air receive slat armor on all four sides. The AAV-7A1 AMTRAC has front and side armor equipped by default since the vehicle does not receive unlocks. (The AMTRAC's armor also does not appear on the gunner's HUD.)
If a panel is struck, it is sacrificed to negate damage inflicted on the vehicle itself. Further impacts against that same side will deal normal damage. Reactive Armor does NOT affect APFSDS-T Shells. The shells damage the vehicle normally.
Once destroyed, the armor plates can be replaced if an engineer repairs the tank to 100% and continues to use the repair tool for a few more seconds on each appropriate side. When done correctly, the HUD icons should reappear.
Reactive Armor returns in Battlefield 4 as a vehicle upgrade.
Unlike its use in Battlefield 3, Reactive Armor in Battlefield 4 does not lessen or reduce damage, but does make it harder for the vehicle to be disabled or immobilized by raising the minimum damage for a mobility hit from 29% to 39%, and a mobility kill from 39% to 44%.
The specialization was first seen in the This is Battlefield 4 Multiplayer trailer.