A tandem-charge weapon is an explosive device or projectile that has two or more stages of detonation. It is effective against cage armor, which is designed to protect an armored vehicle (mostly tanks) against anti-tank munitions.[1] The first stage of the weapon triggers the reactive armor of the target, limiting the attack's effectiveness. However, after the reactive armor has protected the vehicle from the primary attack, it is no longer "reactive" in that location (since reactive armour is primarily a one-time defense solution) and the location is left more vulnerable. The second detonation from the same projectile (which defines it as a tandem charge) attacks the same location as the first detonation where the reactive armor has been compromised. Since the regular armor plating is often the only defense remaining, the tandem charge (second detonation) has an increased likelihood of penetrating the armor.
However, tandem-charges are useful only against SLERA (self-limiting explosive reactive armor) types of reactive armor, not against the NERA (non-energetic reactive armor) and NxRA (non-explosive reactive armor) reactive armor types, since their inner liner is not explosive itself, thus able to withstand the small forward warhead of tandem-charge attack.
The PG-7VR warhead for the RPG-7 rocket launcher and the more modern RPG-29 rocket are examples of tandem charges. Additionally, many American missiles use the tandem charges because they were designed in the Cold War era to counter the reactive armor that was a common feature on Soviet tanks. Examples of American missiles that use tandem charges include the BGM-71 TOW, FGM-148 Javelin and the AGM-114 Hellfire.