A warhead assembly, comprising a cylindrical or conical metal body, having an inner wall with a plurality of channels or grooves extending parallel to a central longitudinal axis. Preformed fragments are inserted in the channels or grooves and a liner with an explosive fill is positioned within the metal body, retaining the preformed fragments in place. The warhead assembly on detonation produces a bimodal distribution of fragments with adequate mass and velocity with optimized mixed fragmentation that defeats or otherwise incapacitates a target or set of targets.