A fast acting active protection system for military vehicles defeats RPG (rocket propelled grenade) threats fired from close ranges. The system minimizes the hazard to troops and civilians nearby. The system uses a plurality of passive sensors to locate the threat and initialize the system. A low cost radar or laser tracker is used as the means to determine range, velocity, and (if required) angular position of the threat. The countermunition used may be one of several choices, with the requisites being that the countermunition provides fast response with low inertia, and is able to damage or destroy the detected threat. A multi-barrel recoilless gun is the weapon of choice. A launching device is used to deploy and aim the countermunition and the tracking means. On board software and electronics are used to control the system.